Merge pull request #132 from chriseth/tupleExpression

Tuple expressions and destructuring assignments

20 files changed, 532 insertions, 105 deletions

diff --git a/libsolidity/AST.h b/libsolidity/AST.h
index 9dd67cc2..fc1db3f3 100644
--- a/libsolidity/AST.h
+++ b/libsolidity/AST.h
@@ -1068,6 +1068,30 @@ private:
 };
 
 /**
+ * Tuple or just parenthesized expression.
+ * Examples: (1, 2), (x,), (x), ()
+ * Individual components might be empty shared pointers (as in the second example).
+ * The respective types in lvalue context are: 2-tuple, 2-tuple (with wildcard), type of x, 0-tuple
+ * Not in lvalue context: 2-tuple, _1_-tuple, type of x, 0-tuple.
+ */
+class TupleExpression: public Expression
+{
+public:
+	TupleExpression(
+		SourceLocation const& _location,
+		std::vector<ASTPointer<Expression>> const& _components
+	):
+		Expression(_location), m_components(_components) {}
+	virtual void accept(ASTVisitor& _visitor) override;
+	virtual void accept(ASTConstVisitor& _visitor) const override;
+
+	std::vector<ASTPointer<Expression>> const& components() const { return m_components; }
+
+private:
+	std::vector<ASTPointer<Expression>> m_components;
+};
+
+/**
  * Operation involving a unary operator, pre- or postfix.
  * Examples: ++i, delete x or !true
  */
diff --git a/libsolidity/ASTForward.h b/libsolidity/ASTForward.h
index 396cf50a..02dd054a 100644
--- a/libsolidity/ASTForward.h
+++ b/libsolidity/ASTForward.h
@@ -69,6 +69,7 @@ class VariableDeclarationStatement;
 class ExpressionStatement;
 class Expression;
 class Assignment;
+class TupleExpression;
 class UnaryOperation;
 class BinaryOperation;
 class FunctionCall;
diff --git a/libsolidity/ASTJsonConverter.cpp b/libsolidity/ASTJsonConverter.cpp
index 4c14f2b2..34012c73 100644
--- a/libsolidity/ASTJsonConverter.cpp
+++ b/libsolidity/ASTJsonConverter.cpp
@@ -226,6 +226,12 @@ bool ASTJsonConverter::visit(Assignment const& _node)
 	return true;
 }
 
+bool ASTJsonConverter::visit(TupleExpression const&)
+{
+	addJsonNode("TupleExpression",{}, true);
+	return true;
+}
+
 bool ASTJsonConverter::visit(UnaryOperation const& _node)
 {
 	addJsonNode("UnaryOperation",
@@ -396,6 +402,11 @@ void ASTJsonConverter::endVisit(Assignment const&)
 	goUp();
 }
 
+void ASTJsonConverter::endVisit(TupleExpression const&)
+{
+	goUp();
+}
+
 void ASTJsonConverter::endVisit(UnaryOperation const&)
 {
 	goUp();
diff --git a/libsolidity/ASTJsonConverter.h b/libsolidity/ASTJsonConverter.h
index 61f87860..a62259e2 100644
--- a/libsolidity/ASTJsonConverter.h
+++ b/libsolidity/ASTJsonConverter.h
@@ -68,6 +68,7 @@ public:
 	bool visit(VariableDeclarationStatement const& _node) override;
 	bool visit(ExpressionStatement const& _node) override;
 	bool visit(Assignment const& _node) override;
+	bool visit(TupleExpression const& _node) override;
 	bool visit(UnaryOperation const& _node) override;
 	bool visit(BinaryOperation const& _node) override;
 	bool visit(FunctionCall const& _node) override;
@@ -99,6 +100,7 @@ public:
 	void endVisit(VariableDeclarationStatement const&) override;
 	void endVisit(ExpressionStatement const&) override;
 	void endVisit(Assignment const&) override;
+	void endVisit(TupleExpression const&) override;
 	void endVisit(UnaryOperation const&) override;
 	void endVisit(BinaryOperation const&) override;
 	void endVisit(FunctionCall const&) override;
diff --git a/libsolidity/ASTPrinter.cpp b/libsolidity/ASTPrinter.cpp
index 534f7c78..cb231842 100644
--- a/libsolidity/ASTPrinter.cpp
+++ b/libsolidity/ASTPrinter.cpp
@@ -256,6 +256,14 @@ bool ASTPrinter::visit(Assignment const& _node)
 	return goDeeper();
 }
 
+bool ASTPrinter::visit(TupleExpression const& _node)
+{
+	writeLine(string("TupleExpression"));
+	printType(_node);
+	printSourcePart(_node);
+	return goDeeper();
+}
+
 bool ASTPrinter::visit(UnaryOperation const& _node)
 {
 	writeLine(string("UnaryOperation (") + (_node.isPrefixOperation() ? "prefix" : "postfix") +
@@ -477,6 +485,11 @@ void ASTPrinter::endVisit(Assignment const&)
 	m_indentation--;
 }
 
+void ASTPrinter::endVisit(TupleExpression const&)
+{
+	m_indentation--;
+}
+
 void ASTPrinter::endVisit(UnaryOperation const&)
 {
 	m_indentation--;
diff --git a/libsolidity/ASTPrinter.h b/libsolidity/ASTPrinter.h
index a12ec0aa..95656436 100644
--- a/libsolidity/ASTPrinter.h
+++ b/libsolidity/ASTPrinter.h
@@ -76,6 +76,7 @@ public:
 	bool visit(VariableDeclarationStatement const& _node) override;
 	bool visit(ExpressionStatement const& _node) override;
 	bool visit(Assignment const& _node) override;
+	bool visit(TupleExpression const& _node) override;
 	bool visit(UnaryOperation const& _node) override;
 	bool visit(BinaryOperation const& _node) override;
 	bool visit(FunctionCall const& _node) override;
@@ -115,6 +116,7 @@ public:
 	void endVisit(VariableDeclarationStatement const&) override;
 	void endVisit(ExpressionStatement const&) override;
 	void endVisit(Assignment const&) override;
+	void endVisit(TupleExpression const&) override;
 	void endVisit(UnaryOperation const&) override;
 	void endVisit(BinaryOperation const&) override;
 	void endVisit(FunctionCall const&) override;
diff --git a/libsolidity/ASTVisitor.h b/libsolidity/ASTVisitor.h
index e665396c..3e50fb28 100644
--- a/libsolidity/ASTVisitor.h
+++ b/libsolidity/ASTVisitor.h
@@ -73,6 +73,7 @@ public:
 	virtual bool visit(VariableDeclarationStatement& _node) { return visitNode(_node); }
 	virtual bool visit(ExpressionStatement& _node) { return visitNode(_node); }
 	virtual bool visit(Assignment& _node) { return visitNode(_node); }
+	virtual bool visit(TupleExpression& _node) { return visitNode(_node); }
 	virtual bool visit(UnaryOperation& _node) { return visitNode(_node); }
 	virtual bool visit(BinaryOperation& _node) { return visitNode(_node); }
 	virtual bool visit(FunctionCall& _node) { return visitNode(_node); }
@@ -113,6 +114,7 @@ public:
 	virtual void endVisit(VariableDeclarationStatement& _node) { endVisitNode(_node); }
 	virtual void endVisit(ExpressionStatement& _node) { endVisitNode(_node); }
 	virtual void endVisit(Assignment& _node) { endVisitNode(_node); }
+	virtual void endVisit(TupleExpression& _node) { endVisitNode(_node); }
 	virtual void endVisit(UnaryOperation& _node) { endVisitNode(_node); }
 	virtual void endVisit(BinaryOperation& _node) { endVisitNode(_node); }
 	virtual void endVisit(FunctionCall& _node) { endVisitNode(_node); }
@@ -165,6 +167,7 @@ public:
 	virtual bool visit(VariableDeclarationStatement const& _node) { return visitNode(_node); }
 	virtual bool visit(ExpressionStatement const& _node) { return visitNode(_node); }
 	virtual bool visit(Assignment const& _node) { return visitNode(_node); }
+	virtual bool visit(TupleExpression const& _node) { return visitNode(_node); }
 	virtual bool visit(UnaryOperation const& _node) { return visitNode(_node); }
 	virtual bool visit(BinaryOperation const& _node) { return visitNode(_node); }
 	virtual bool visit(FunctionCall const& _node) { return visitNode(_node); }
@@ -205,6 +208,7 @@ public:
 	virtual void endVisit(VariableDeclarationStatement const& _node) { endVisitNode(_node); }
 	virtual void endVisit(ExpressionStatement const& _node) { endVisitNode(_node); }
 	virtual void endVisit(Assignment const& _node) { endVisitNode(_node); }
+	virtual void endVisit(TupleExpression const& _node) { endVisitNode(_node); }
 	virtual void endVisit(UnaryOperation const& _node) { endVisitNode(_node); }
 	virtual void endVisit(BinaryOperation const& _node) { endVisitNode(_node); }
 	virtual void endVisit(FunctionCall const& _node) { endVisitNode(_node); }
diff --git a/libsolidity/AST_accept.h b/libsolidity/AST_accept.h
index 994bfc8d..eb1f6098 100644
--- a/libsolidity/AST_accept.h
+++ b/libsolidity/AST_accept.h
@@ -559,6 +559,24 @@ void Assignment::accept(ASTConstVisitor& _visitor) const
 	_visitor.endVisit(*this);
 }
 
+void TupleExpression::accept(ASTVisitor& _visitor)
+{
+	if (_visitor.visit(*this))
+		for (auto const& component: m_components)
+			if (component)
+				component->accept(_visitor);
+	_visitor.endVisit(*this);
+}
+
+void TupleExpression::accept(ASTConstVisitor& _visitor) const
+{
+	if (_visitor.visit(*this))
+		for (auto const& component: m_components)
+			if (component)
+				component->accept(_visitor);
+	_visitor.endVisit(*this);
+}
+
 void UnaryOperation::accept(ASTVisitor& _visitor)
 {
 	if (_visitor.visit(*this))
diff --git a/libsolidity/Compiler.cpp b/libsolidity/Compiler.cpp
index 7c6c7831..679704ba 100644
--- a/libsolidity/Compiler.cpp
+++ b/libsolidity/Compiler.cpp
@@ -597,13 +597,20 @@ bool Compiler::visit(Break const& _breakStatement)
 bool Compiler::visit(Return const& _return)
 {
 	CompilerContext::LocationSetter locationSetter(m_context, _return);
-	//@todo modifications are needed to make this work with functions returning multiple values
 	if (Expression const* expression = _return.expression())
 	{
 		solAssert(_return.annotation().functionReturnParameters, "Invalid return parameters pointer.");
-		VariableDeclaration const& firstVariable = *_return.annotation().functionReturnParameters->parameters().front();
-		compileExpression(*expression, firstVariable.annotation().type);
-		CompilerUtils(m_context).moveToStackVariable(firstVariable);
+		vector<ASTPointer<VariableDeclaration>> const& returnParameters =
+			_return.annotation().functionReturnParameters->parameters();
+		TypePointers types;
+		for (auto const& retVariable: returnParameters)
+			types.push_back(retVariable->annotation().type);
+
+		TypePointer expectedType = types.size() == 1 ? types.front() : make_shared<TupleType>(types);
+		compileExpression(*expression, expectedType);
+
+		for (auto const& retVariable: boost::adaptors::reverse(returnParameters))
+			CompilerUtils(m_context).moveToStackVariable(*retVariable);
 	}
 	for (unsigned i = 0; i < m_stackCleanupForReturn; ++i)
 		m_context << eth::Instruction::POP;
@@ -637,6 +644,7 @@ bool Compiler::visit(VariableDeclarationStatement const& _variableDeclarationSta
 		for (size_t i = 0; i < assignments.size(); ++i)
 		{
 			size_t j = assignments.size() - i - 1;
+			solAssert(!!valueTypes[j], "");
 			VariableDeclaration const* varDecl = assignments[j];
 			if (!varDecl)
 				utils.popStackElement(*valueTypes[j]);
diff --git a/libsolidity/CompilerUtils.cpp b/libsolidity/CompilerUtils.cpp
index e1152202..f0dea708 100644
--- a/libsolidity/CompilerUtils.cpp
+++ b/libsolidity/CompilerUtils.cpp
@@ -550,6 +550,61 @@ void CompilerUtils::convertType(Type const& _typeOnStack, Type const& _targetTyp
 		}
 		break;
 	}
+	case Type::Category::Tuple:
+	{
+		TupleType const& sourceTuple = dynamic_cast<TupleType const&>(_typeOnStack);
+		TupleType const& targetTuple = dynamic_cast<TupleType const&>(_targetType);
+		// fillRight: remove excess values at right side, !fillRight: remove eccess values at left side
+		bool fillRight = !targetTuple.components().empty() && (
+			!targetTuple.components().back() ||
+			targetTuple.components().front()
+		);
+		unsigned depth = sourceTuple.sizeOnStack();
+		for (size_t i = 0; i < sourceTuple.components().size(); ++i)
+		{
+			TypePointer sourceType = sourceTuple.components()[i];
+			TypePointer targetType;
+			if (fillRight && i < targetTuple.components().size())
+				targetType = targetTuple.components()[i];
+			else if (!fillRight && targetTuple.components().size() + i >= sourceTuple.components().size())
+				targetType = targetTuple.components()[targetTuple.components().size() - (sourceTuple.components().size() - i)];
+			if (!sourceType)
+			{
+				solAssert(!targetType, "");
+				continue;
+			}
+			unsigned sourceSize = sourceType->sizeOnStack();
+			unsigned targetSize = targetType ? targetType->sizeOnStack() : 0;
+			if (!targetType || *sourceType != *targetType || _cleanupNeeded)
+			{
+				if (targetType)
+				{
+					if (sourceSize > 0)
+						copyToStackTop(depth, sourceSize);
+					convertType(*sourceType, *targetType, _cleanupNeeded);
+				}
+				if (sourceSize > 0 || targetSize > 0)
+				{
+					// Move it back into its place.
+					for (unsigned j = 0; j < min(sourceSize, targetSize); ++j)
+						m_context <<
+							eth::swapInstruction(depth + targetSize - sourceSize) <<
+							eth::Instruction::POP;
+					// Value shrank
+					for (unsigned j = targetSize; j < sourceSize; ++j)
+					{
+						moveToStackTop(depth - 1, 1);
+						m_context << eth::Instruction::POP;
+					}
+					// Value grew
+					if (targetSize > sourceSize)
+						moveIntoStack(depth + targetSize - sourceSize, targetSize - sourceSize);
+				}
+			}
+			depth -= sourceSize;
+		}
+		break;
+	}
 	default:
 		// All other types should not be convertible to non-equal types.
 		solAssert(_typeOnStack == _targetType, "Invalid type conversion requested.");
@@ -631,18 +686,20 @@ void CompilerUtils::copyToStackTop(unsigned _stackDepth, unsigned _itemSize)
 		m_context << eth::dupInstruction(_stackDepth);
 }
 
-void CompilerUtils::moveToStackTop(unsigned _stackDepth)
+void CompilerUtils::moveToStackTop(unsigned _stackDepth, unsigned _itemSize)
 {
 	solAssert(_stackDepth <= 15, "Stack too deep, try removing local variables.");
-	for (unsigned i = 0; i < _stackDepth; ++i)
-		m_context << eth::swapInstruction(1 + i);
+	for (unsigned j = 0; j < _itemSize; ++j)
+		for (unsigned i = 0; i < _stackDepth + _itemSize - 1; ++i)
+			m_context << eth::swapInstruction(1 + i);
 }
 
-void CompilerUtils::moveIntoStack(unsigned _stackDepth)
+void CompilerUtils::moveIntoStack(unsigned _stackDepth, unsigned _itemSize)
 {
 	solAssert(_stackDepth <= 16, "Stack too deep, try removing local variables.");
-	for (unsigned i = _stackDepth; i > 0; --i)
-		m_context << eth::swapInstruction(i);
+	for (unsigned j = 0; j < _itemSize; ++j)
+		for (unsigned i = _stackDepth; i > 0; --i)
+			m_context << eth::swapInstruction(i + _itemSize - 1);
 }
 
 void CompilerUtils::popStackElement(Type const& _type)
diff --git a/libsolidity/CompilerUtils.h b/libsolidity/CompilerUtils.h
index f335eed5..01b9f422 100644
--- a/libsolidity/CompilerUtils.h
+++ b/libsolidity/CompilerUtils.h
@@ -124,10 +124,11 @@ public:
 	/// Copies an item that occupies @a _itemSize stack slots from a stack depth of @a _stackDepth
 	/// to the top of the stack.
 	void copyToStackTop(unsigned _stackDepth, unsigned _itemSize);
-	/// Moves a single stack element (with _stackDepth items on top of it) to the top of the stack.
-	void moveToStackTop(unsigned _stackDepth);
-	/// Moves a single stack element past @a _stackDepth other stack elements
-	void moveIntoStack(unsigned _stackDepth);
+	/// Moves an item that occupies @a _itemSize stack slots and has items occupying @a _stackDepth
+	/// slots above it to the top of the stack.
+	void moveToStackTop(unsigned _stackDepth, unsigned _itemSize = 1);
+	/// Moves @a _itemSize elements past @a _stackDepth other stack elements
+	void moveIntoStack(unsigned _stackDepth, unsigned _itemSize = 1);
 	/// Removes the current value from the top of the stack.
 	void popStackElement(Type const& _type);
 	/// Removes element from the top of the stack _amount times.
diff --git a/libsolidity/ExpressionCompiler.cpp b/libsolidity/ExpressionCompiler.cpp
index 85302afc..fde88a00 100644
--- a/libsolidity/ExpressionCompiler.cpp
+++ b/libsolidity/ExpressionCompiler.cpp
@@ -179,17 +179,12 @@ bool ExpressionCompiler::visit(Assignment const& _assignment)
 {
 	CompilerContext::LocationSetter locationSetter(m_context, _assignment);
 	_assignment.rightHandSide().accept(*this);
-	TypePointer type = _assignment.rightHandSide().annotation().type;
-	if (!_assignment.annotation().type->dataStoredIn(DataLocation::Storage))
-	{
-		utils().convertType(*type, *_assignment.annotation().type);
-		type = _assignment.annotation().type;
-	}
-	else
-	{
-		utils().convertType(*type, *type->mobileType());
-		type = type->mobileType();
-	}
+	// Perform some conversion already. This will convert storage types to memory and literals
+	// to their actual type, but will not convert e.g. memory to storage.
+	TypePointer type = _assignment.rightHandSide().annotation().type->closestTemporaryType(
+		_assignment.leftHandSide().annotation().type
+	);
+	utils().convertType(*_assignment.rightHandSide().annotation().type, *type);
 
 	_assignment.leftHandSide().accept(*this);
 	solAssert(!!m_currentLValue, "LValue not retrieved.");
@@ -221,6 +216,26 @@ bool ExpressionCompiler::visit(Assignment const& _assignment)
 	return false;
 }
 
+bool ExpressionCompiler::visit(TupleExpression const& _tuple)
+{
+	vector<unique_ptr<LValue>> lvalues;
+	for (auto const& component: _tuple.components())
+		if (component)
+		{
+			component->accept(*this);
+			if (_tuple.annotation().lValueRequested)
+			{
+				solAssert(!!m_currentLValue, "");
+				lvalues.push_back(move(m_currentLValue));
+			}
+		}
+		else if (_tuple.annotation().lValueRequested)
+			lvalues.push_back(unique_ptr<LValue>());
+	if (_tuple.annotation().lValueRequested)
+		m_currentLValue.reset(new TupleObject(m_context, move(lvalues)));
+	return false;
+}
+
 bool ExpressionCompiler::visit(UnaryOperation const& _unaryOperation)
 {
 	CompilerContext::LocationSetter locationSetter(m_context, _unaryOperation);
@@ -649,9 +664,8 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 			// stack: newLength storageSlot slotOffset
 			arguments[0]->accept(*this);
 			// stack: newLength storageSlot slotOffset argValue
-			TypePointer type = arguments[0]->annotation().type;
-			utils().convertType(*type, *arrayType->baseType());
-			type = arrayType->baseType();
+			TypePointer type = arguments[0]->annotation().type->closestTemporaryType(arrayType->baseType());
+			utils().convertType(*arguments[0]->annotation().type, *type);
 			utils().moveToStackTop(1 + type->sizeOnStack());
 			utils().moveToStackTop(1 + type->sizeOnStack());
 			// stack: newLength argValue storageSlot slotOffset
diff --git a/libsolidity/ExpressionCompiler.h b/libsolidity/ExpressionCompiler.h
index d8fef5af..44d27ea2 100644
--- a/libsolidity/ExpressionCompiler.h
+++ b/libsolidity/ExpressionCompiler.h
@@ -72,6 +72,7 @@ public:
 
 private:
 	virtual bool visit(Assignment const& _assignment) override;
+	virtual bool visit(TupleExpression const& _tuple) override;
 	virtual bool visit(UnaryOperation const& _unaryOperation) override;
 	virtual bool visit(BinaryOperation const& _binaryOperation) override;
 	virtual bool visit(FunctionCall const& _functionCall) override;
diff --git a/libsolidity/LValue.cpp b/libsolidity/LValue.cpp
index 9f33e846..ac04ebef 100644
--- a/libsolidity/LValue.cpp
+++ b/libsolidity/LValue.cpp
@@ -32,9 +32,9 @@ using namespace solidity;
 
 
 StackVariable::StackVariable(CompilerContext& _compilerContext, VariableDeclaration const& _declaration):
-	LValue(_compilerContext, *_declaration.annotation().type),
+	LValue(_compilerContext, _declaration.annotation().type.get()),
 	m_baseStackOffset(m_context.baseStackOffsetOfVariable(_declaration)),
-	m_size(m_dataType.sizeOnStack())
+	m_size(m_dataType->sizeOnStack())
 {
 }
 
@@ -70,23 +70,23 @@ void StackVariable::storeValue(Type const&, SourceLocation const& _location, boo
 
 void StackVariable::setToZero(SourceLocation const& _location, bool) const
 {
-	CompilerUtils(m_context).pushZeroValue(m_dataType);
-	storeValue(m_dataType, _location, true);
+	CompilerUtils(m_context).pushZeroValue(*m_dataType);
+	storeValue(*m_dataType, _location, true);
 }
 
 MemoryItem::MemoryItem(CompilerContext& _compilerContext, Type const& _type, bool _padded):
-	LValue(_compilerContext, _type),
+	LValue(_compilerContext, &_type),
 	m_padded(_padded)
 {
 }
 
 void MemoryItem::retrieveValue(SourceLocation const&, bool _remove) const
 {
-	if (m_dataType.isValueType())
+	if (m_dataType->isValueType())
 	{
 		if (!_remove)
 			m_context << eth::Instruction::DUP1;
-		CompilerUtils(m_context).loadFromMemoryDynamic(m_dataType, false, m_padded, false);
+		CompilerUtils(m_context).loadFromMemoryDynamic(*m_dataType, false, m_padded, false);
 	}
 	else
 		m_context << eth::Instruction::MLOAD;
@@ -95,24 +95,24 @@ void MemoryItem::retrieveValue(SourceLocation const&, bool _remove) const
 void MemoryItem::storeValue(Type const& _sourceType, SourceLocation const&, bool _move) const
 {
 	CompilerUtils utils(m_context);
-	if (m_dataType.isValueType())
+	if (m_dataType->isValueType())
 	{
 		solAssert(_sourceType.isValueType(), "");
 		utils.moveIntoStack(_sourceType.sizeOnStack());
-		utils.convertType(_sourceType, m_dataType, true);
+		utils.convertType(_sourceType, *m_dataType, true);
 		if (!_move)
 		{
-			utils.moveToStackTop(m_dataType.sizeOnStack());
-			utils.copyToStackTop(2, m_dataType.sizeOnStack());
+			utils.moveToStackTop(m_dataType->sizeOnStack());
+			utils.copyToStackTop(2, m_dataType->sizeOnStack());
 		}
-		utils.storeInMemoryDynamic(m_dataType, m_padded);
+		utils.storeInMemoryDynamic(*m_dataType, m_padded);
 		m_context << eth::Instruction::POP;
 	}
 	else
 	{
-		solAssert(_sourceType == m_dataType, "Conversion not implemented for assignment to memory.");
+		solAssert(_sourceType == *m_dataType, "Conversion not implemented for assignment to memory.");
 
-		solAssert(m_dataType.sizeOnStack() == 1, "");
+		solAssert(m_dataType->sizeOnStack() == 1, "");
 		if (!_move)
 			m_context << eth::Instruction::DUP2 << eth::Instruction::SWAP1;
 		// stack: [value] value lvalue
@@ -126,8 +126,8 @@ void MemoryItem::setToZero(SourceLocation const&, bool _removeReference) const
 	CompilerUtils utils(m_context);
 	if (!_removeReference)
 		m_context << eth::Instruction::DUP1;
-	utils.pushZeroValue(m_dataType);
-	utils.storeInMemoryDynamic(m_dataType, m_padded);
+	utils.pushZeroValue(*m_dataType);
+	utils.storeInMemoryDynamic(*m_dataType, m_padded);
 	m_context << eth::Instruction::POP;
 }
 
@@ -139,21 +139,21 @@ StorageItem::StorageItem(CompilerContext& _compilerContext, VariableDeclaration
 }
 
 StorageItem::StorageItem(CompilerContext& _compilerContext, Type const& _type):
-	LValue(_compilerContext, _type)
+	LValue(_compilerContext, &_type)
 {
-	if (m_dataType.isValueType())
+	if (m_dataType->isValueType())
 	{
-		solAssert(m_dataType.storageSize() == m_dataType.sizeOnStack(), "");
-		solAssert(m_dataType.storageSize() == 1, "Invalid storage size.");
+		solAssert(m_dataType->storageSize() == m_dataType->sizeOnStack(), "");
+		solAssert(m_dataType->storageSize() == 1, "Invalid storage size.");
 	}
 }
 
 void StorageItem::retrieveValue(SourceLocation const&, bool _remove) const
 {
 	// stack: storage_key storage_offset
-	if (!m_dataType.isValueType())
+	if (!m_dataType->isValueType())
 	{
-		solAssert(m_dataType.sizeOnStack() == 1, "Invalid storage ref size.");
+		solAssert(m_dataType->sizeOnStack() == 1, "Invalid storage ref size.");
 		if (_remove)
 			m_context << eth::Instruction::POP; // remove byte offset
 		else
@@ -162,22 +162,22 @@ void StorageItem::retrieveValue(SourceLocation const&, bool _remove) const
 	}
 	if (!_remove)
 		CompilerUtils(m_context).copyToStackTop(sizeOnStack(), sizeOnStack());
-	if (m_dataType.storageBytes() == 32)
+	if (m_dataType->storageBytes() == 32)
 		m_context << eth::Instruction::POP << eth::Instruction::SLOAD;
 	else
 	{
 		m_context
 			<< eth::Instruction::SWAP1 << eth::Instruction::SLOAD << eth::Instruction::SWAP1
 			<< u256(0x100) << eth::Instruction::EXP << eth::Instruction::SWAP1 << eth::Instruction::DIV;
-		if (m_dataType.category() == Type::Category::FixedBytes)
-			m_context << (u256(0x1) << (256 - 8 * m_dataType.storageBytes())) << eth::Instruction::MUL;
+		if (m_dataType->category() == Type::Category::FixedBytes)
+			m_context << (u256(0x1) << (256 - 8 * m_dataType->storageBytes())) << eth::Instruction::MUL;
 		else if (
-			m_dataType.category() == Type::Category::Integer &&
-			dynamic_cast<IntegerType const&>(m_dataType).isSigned()
+			m_dataType->category() == Type::Category::Integer &&
+			dynamic_cast<IntegerType const&>(*m_dataType).isSigned()
 		)
-			m_context << u256(m_dataType.storageBytes() - 1) << eth::Instruction::SIGNEXTEND;
+			m_context << u256(m_dataType->storageBytes() - 1) << eth::Instruction::SIGNEXTEND;
 		else
-			m_context << ((u256(0x1) << (8 * m_dataType.storageBytes())) - 1) << eth::Instruction::AND;
+			m_context << ((u256(0x1) << (8 * m_dataType->storageBytes())) - 1) << eth::Instruction::AND;
 	}
 }
 
@@ -185,11 +185,11 @@ void StorageItem::storeValue(Type const& _sourceType, SourceLocation const& _loc
 {
 	CompilerUtils utils(m_context);
 	// stack: value storage_key storage_offset
-	if (m_dataType.isValueType())
+	if (m_dataType->isValueType())
 	{
-		solAssert(m_dataType.storageBytes() <= 32, "Invalid storage bytes size.");
-		solAssert(m_dataType.storageBytes() > 0, "Invalid storage bytes size.");
-		if (m_dataType.storageBytes() == 32)
+		solAssert(m_dataType->storageBytes() <= 32, "Invalid storage bytes size.");
+		solAssert(m_dataType->storageBytes() > 0, "Invalid storage bytes size.");
+		if (m_dataType->storageBytes() == 32)
 		{
 			// offset should be zero
 			m_context << eth::Instruction::POP;
@@ -207,24 +207,24 @@ void StorageItem::storeValue(Type const& _sourceType, SourceLocation const& _loc
 			// stack: value storege_ref multiplier old_full_value
 			// clear bytes in old value
 			m_context
-				<< eth::Instruction::DUP2 << ((u256(1) << (8 * m_dataType.storageBytes())) - 1)
+				<< eth::Instruction::DUP2 << ((u256(1) << (8 * m_dataType->storageBytes())) - 1)
 				<< eth::Instruction::MUL;
 			m_context << eth::Instruction::NOT << eth::Instruction::AND;
 			// stack: value storage_ref multiplier cleared_value
 			m_context
 				<< eth::Instruction::SWAP1 << eth::Instruction::DUP4;
 			// stack: value storage_ref cleared_value multiplier value
-			if (m_dataType.category() == Type::Category::FixedBytes)
+			if (m_dataType->category() == Type::Category::FixedBytes)
 				m_context
-					<< (u256(0x1) << (256 - 8 * dynamic_cast<FixedBytesType const&>(m_dataType).numBytes()))
+					<< (u256(0x1) << (256 - 8 * dynamic_cast<FixedBytesType const&>(*m_dataType).numBytes()))
 					<< eth::Instruction::SWAP1 << eth::Instruction::DIV;
 			else if (
-				m_dataType.category() == Type::Category::Integer &&
-				dynamic_cast<IntegerType const&>(m_dataType).isSigned()
+				m_dataType->category() == Type::Category::Integer &&
+				dynamic_cast<IntegerType const&>(*m_dataType).isSigned()
 			)
 				// remove the higher order bits
 				m_context
-					<< (u256(1) << (8 * (32 - m_dataType.storageBytes())))
+					<< (u256(1) << (8 * (32 - m_dataType->storageBytes())))
 					<< eth::Instruction::SWAP1
 					<< eth::Instruction::DUP2
 					<< eth::Instruction::MUL
@@ -239,23 +239,24 @@ void StorageItem::storeValue(Type const& _sourceType, SourceLocation const& _loc
 	else
 	{
 		solAssert(
-			_sourceType.category() == m_dataType.category(),
+			_sourceType.category() == m_dataType->category(),
 			"Wrong type conversation for assignment.");
-		if (m_dataType.category() == Type::Category::Array)
+		if (m_dataType->category() == Type::Category::Array)
 		{
 			m_context << eth::Instruction::POP; // remove byte offset
 			ArrayUtils(m_context).copyArrayToStorage(
-						dynamic_cast<ArrayType const&>(m_dataType),
-						dynamic_cast<ArrayType const&>(_sourceType));
+				dynamic_cast<ArrayType const&>(*m_dataType),
+				dynamic_cast<ArrayType const&>(_sourceType)
+			);
 			if (_move)
 				m_context << eth::Instruction::POP;
 		}
-		else if (m_dataType.category() == Type::Category::Struct)
+		else if (m_dataType->category() == Type::Category::Struct)
 		{
 			// stack layout: source_ref target_ref target_offset
 			// note that we have structs, so offset should be zero and are ignored
 			m_context << eth::Instruction::POP;
-			auto const& structType = dynamic_cast<StructType const&>(m_dataType);
+			auto const& structType = dynamic_cast<StructType const&>(*m_dataType);
 			auto const& sourceType = dynamic_cast<StructType const&>(_sourceType);
 			solAssert(
 				structType.structDefinition() == sourceType.structDefinition(),
@@ -313,18 +314,18 @@ void StorageItem::storeValue(Type const& _sourceType, SourceLocation const& _loc
 
 void StorageItem::setToZero(SourceLocation const&, bool _removeReference) const
 {
-	if (m_dataType.category() == Type::Category::Array)
+	if (m_dataType->category() == Type::Category::Array)
 	{
 		if (!_removeReference)
 			CompilerUtils(m_context).copyToStackTop(sizeOnStack(), sizeOnStack());
-		ArrayUtils(m_context).clearArray(dynamic_cast<ArrayType const&>(m_dataType));
+		ArrayUtils(m_context).clearArray(dynamic_cast<ArrayType const&>(*m_dataType));
 	}
-	else if (m_dataType.category() == Type::Category::Struct)
+	else if (m_dataType->category() == Type::Category::Struct)
 	{
 		// stack layout: storage_key storage_offset
 		// @todo this can be improved: use StorageItem for non-value types, and just store 0 in
 		// all slots that contain value types later.
-		auto const& structType = dynamic_cast<StructType const&>(m_dataType);
+		auto const& structType = dynamic_cast<StructType const&>(*m_dataType);
 		for (auto const& member: structType.members())
 		{
 			// zero each member that is not a mapping
@@ -342,10 +343,10 @@ void StorageItem::setToZero(SourceLocation const&, bool _removeReference) const
 	}
 	else
 	{
-		solAssert(m_dataType.isValueType(), "Clearing of unsupported type requested: " + m_dataType.toString());
+		solAssert(m_dataType->isValueType(), "Clearing of unsupported type requested: " + m_dataType->toString());
 		if (!_removeReference)
 			CompilerUtils(m_context).copyToStackTop(sizeOnStack(), sizeOnStack());
-		if (m_dataType.storageBytes() == 32)
+		if (m_dataType->storageBytes() == 32)
 		{
 			// offset should be zero
 			m_context
@@ -361,7 +362,7 @@ void StorageItem::setToZero(SourceLocation const&, bool _removeReference) const
 			// stack: storege_ref multiplier old_full_value
 			// clear bytes in old value
 			m_context
-				<< eth::Instruction::SWAP1 << ((u256(1) << (8 * m_dataType.storageBytes())) - 1)
+				<< eth::Instruction::SWAP1 << ((u256(1) << (8 * m_dataType->storageBytes())) - 1)
 				<< eth::Instruction::MUL;
 			m_context << eth::Instruction::NOT << eth::Instruction::AND;
 			// stack: storage_ref cleared_value
@@ -374,7 +375,7 @@ void StorageItem::setToZero(SourceLocation const&, bool _removeReference) const
 static FixedBytesType byteType(1);
 
 StorageByteArrayElement::StorageByteArrayElement(CompilerContext& _compilerContext):
-	LValue(_compilerContext, byteType)
+	LValue(_compilerContext, &byteType)
 {
 }
 
@@ -427,7 +428,7 @@ void StorageByteArrayElement::setToZero(SourceLocation const&, bool _removeRefer
 }
 
 StorageArrayLength::StorageArrayLength(CompilerContext& _compilerContext, const ArrayType& _arrayType):
-	LValue(_compilerContext, *_arrayType.memberType("length")),
+	LValue(_compilerContext, _arrayType.memberType("length").get()),
 	m_arrayType(_arrayType)
 {
 	solAssert(m_arrayType.isDynamicallySized(), "");
@@ -455,3 +456,91 @@ void StorageArrayLength::setToZero(SourceLocation const&, bool _removeReference)
 		m_context << eth::Instruction::DUP1;
 	ArrayUtils(m_context).clearDynamicArray(m_arrayType);
 }
+
+
+TupleObject::TupleObject(
+	CompilerContext& _compilerContext,
+	std::vector<std::unique_ptr<LValue>>&& _lvalues
+):
+	LValue(_compilerContext), m_lvalues(move(_lvalues))
+{
+}
+
+unsigned TupleObject::sizeOnStack() const
+{
+	unsigned size = 0;
+	for (auto const& lv: m_lvalues)
+		if (lv)
+			size += lv->sizeOnStack();
+	return size;
+}
+
+void TupleObject::retrieveValue(SourceLocation const& _location, bool _remove) const
+{
+	unsigned initialDepth = sizeOnStack();
+	unsigned initialStack = m_context.stackHeight();
+	for (auto const& lv: m_lvalues)
+		if (lv)
+		{
+			solAssert(initialDepth + m_context.stackHeight() >= initialStack, "");
+			unsigned depth = initialDepth + m_context.stackHeight() - initialStack;
+			if (lv->sizeOnStack() > 0)
+			{
+				if (_remove && depth > lv->sizeOnStack())
+					CompilerUtils(m_context).moveToStackTop(depth, depth - lv->sizeOnStack());
+				else if (!_remove && depth > 0)
+					CompilerUtils(m_context).copyToStackTop(depth, lv->sizeOnStack());
+			}
+			lv->retrieveValue(_location, true);
+		}
+}
+
+void TupleObject::storeValue(Type const& _sourceType, SourceLocation const& _location, bool) const
+{
+	// values are below the lvalue references
+	unsigned valuePos = sizeOnStack();
+	TypePointers const& valueTypes = dynamic_cast<TupleType const&>(_sourceType).components();
+	solAssert(valueTypes.size() == m_lvalues.size(), "");
+	// valuePos .... refPos ...
+	// We will assign from right to left to optimize stack layout.
+	for (size_t i = 0; i < m_lvalues.size(); ++i)
+	{
+		unique_ptr<LValue> const& lvalue = m_lvalues[m_lvalues.size() - i - 1];
+		TypePointer const& valType = valueTypes[valueTypes.size() - i - 1];
+		unsigned stackHeight = m_context.stackHeight();
+		solAssert(!valType == !lvalue, "");
+		if (!lvalue)
+			continue;
+		valuePos += valType->sizeOnStack();
+		// copy value to top
+		CompilerUtils(m_context).copyToStackTop(valuePos, valType->sizeOnStack());
+		// move lvalue ref above value
+		CompilerUtils(m_context).moveToStackTop(valType->sizeOnStack(), lvalue->sizeOnStack());
+		lvalue->storeValue(*valType, _location, true);
+		valuePos += m_context.stackHeight() - stackHeight;
+	}
+	// As the type of an assignment to a tuple type is the empty tuple, we always move.
+	CompilerUtils(m_context).popStackElement(_sourceType);
+}
+
+void TupleObject::setToZero(SourceLocation const& _location, bool _removeReference) const
+{
+	if (_removeReference)
+	{
+		for (size_t i = 0; i < m_lvalues.size(); ++i)
+			if (m_lvalues[m_lvalues.size() - i])
+				m_lvalues[m_lvalues.size() - i]->setToZero(_location, true);
+	}
+	else
+	{
+		unsigned depth = sizeOnStack();
+		for (auto const& val: m_lvalues)
+			if (val)
+			{
+				if (val->sizeOnStack() > 0)
+					CompilerUtils(m_context).copyToStackTop(depth, val->sizeOnStack());
+				val->setToZero(_location, false);
+				depth -= val->sizeOnStack();
+			}
+	}
+}
diff --git a/libsolidity/LValue.h b/libsolidity/LValue.h
index cbbfb102..94c8d3b8 100644
--- a/libsolidity/LValue.h
+++ b/libsolidity/LValue.h
@@ -23,6 +23,7 @@
 #pragma once
 
 #include <memory>
+#include <vector>
 #include <libevmasm/SourceLocation.h>
 #include <libsolidity/ArrayUtils.h>
 
@@ -33,6 +34,7 @@ namespace solidity
 
 class Declaration;
 class Type;
+class TupleType;
 class ArrayType;
 class CompilerContext;
 class VariableDeclaration;
@@ -43,7 +45,7 @@ class VariableDeclaration;
 class LValue
 {
 protected:
-	LValue(CompilerContext& _compilerContext, Type const& _dataType):
+	explicit LValue(CompilerContext& _compilerContext, Type const* _dataType = nullptr):
 		m_context(_compilerContext), m_dataType(_dataType) {}
 
 public:
@@ -68,7 +70,7 @@ public:
 
 protected:
 	CompilerContext& m_context;
-	Type const& m_dataType;
+	Type const* m_dataType;
 };
 
 /**
@@ -193,5 +195,30 @@ private:
 	ArrayType const& m_arrayType;
 };
 
+/**
+ * Tuple object that can itself hold several LValues.
+ */
+class TupleObject: public LValue
+{
+public:
+	/// Constructs the LValue assuming that the other LValues are present on the stack.
+	/// Empty unique_ptrs are possible if e.g. some values should be ignored during assignment.
+	TupleObject(CompilerContext& _compilerContext, std::vector<std::unique_ptr<LValue>>&& _lvalues);
+	virtual unsigned sizeOnStack() const;
+	virtual void retrieveValue(SourceLocation const& _location, bool _remove = false) const override;
+	virtual void storeValue(
+		Type const& _sourceType,
+		SourceLocation const& _location = SourceLocation(),
+		bool _move = false
+	) const override;
+	virtual void setToZero(
+		SourceLocation const& _location = SourceLocation(),
+		bool _removeReference = true
+	) const override;
+
+private:
+	std::vector<std::unique_ptr<LValue>> m_lvalues;
+};
+
 }
 }
diff --git a/libsolidity/Parser.cpp b/libsolidity/Parser.cpp
index ab2d0094..1bb16b84 100644
--- a/libsolidity/Parser.cpp
+++ b/libsolidity/Parser.cpp
@@ -806,6 +806,7 @@ ASTPointer<VariableDeclarationStatement> Parser::parseVariableDeclarationStateme
 				)
 				{
 					ASTNodeFactory varDeclNodeFactory(*this);
+					varDeclNodeFactory.markEndPosition();
 					ASTPointer<ASTString> name = expectIdentifierToken();
 					var = varDeclNodeFactory.createNode<VariableDeclaration>(
 						ASTPointer<TypeName>(),
@@ -1009,10 +1010,25 @@ ASTPointer<Expression> Parser::parsePrimaryExpression()
 		break;
 	case Token::LParen:
 	{
+		// Tuple or parenthesized expression.
+		// Special cases: () is empty tuple type, (x) is not a real tuple, (x,) is one-dimensional tuple
 		m_scanner->next();
-		ASTPointer<Expression> expression = parseExpression();
+		vector<ASTPointer<Expression>> components;
+		if (m_scanner->currentToken() != Token::RParen)
+			while (true)
+			{
+				if (m_scanner->currentToken() != Token::Comma && m_scanner->currentToken() != Token::RParen)
+					components.push_back(parseExpression());
+				else
+					components.push_back(ASTPointer<Expression>());
+				if (m_scanner->currentToken() == Token::RParen)
+					break;
+				else if (m_scanner->currentToken() == Token::Comma)
+					m_scanner->next();
+			}
+		nodeFactory.markEndPosition();
 		expectToken(Token::RParen);
-		return expression;
+		return nodeFactory.createNode<TupleExpression>(components);
 	}
 	default:
 		if (Token::isElementaryTypeName(token))
diff --git a/libsolidity/TypeChecker.cpp b/libsolidity/TypeChecker.cpp
index ca5b1eb7..dcaecdfb 100644
--- a/libsolidity/TypeChecker.cpp
+++ b/libsolidity/TypeChecker.cpp
@@ -560,13 +560,31 @@ void TypeChecker::endVisit(Return const& _return)
 		return;
 	ParameterList const* params = _return.annotation().functionReturnParameters;
 	if (!params)
+	{
 		typeError(_return, "Return arguments not allowed.");
+		return;
+	}
+	TypePointers returnTypes;
+	for (auto const& var: params->parameters())
+		returnTypes.push_back(type(*var));
+	if (auto tupleType = dynamic_cast<TupleType const*>(type(*_return.expression()).get()))
+	{
+		if (tupleType->components().size() != params->parameters().size())
+			typeError(_return, "Different number of arguments in return statement than in returns declaration.");
+		else if (!tupleType->isImplicitlyConvertibleTo(TupleType(returnTypes)))
+			typeError(
+				*_return.expression(),
+				"Return argument type " +
+				type(*_return.expression())->toString() +
+				" is not implicitly convertible to expected type " +
+				TupleType(returnTypes).toString(false) +
+				"."
+			);
+	}
 	else if (params->parameters().size() != 1)
 		typeError(_return, "Different number of arguments in return statement than in returns declaration.");
 	else
 	{
-		// this could later be changed such that the paramaters type is an anonymous struct type,
-		// but for now, we only allow one return parameter
 		TypePointer const& expected = type(*params->parameters().front());
 		if (!type(*_return.expression())->isImplicitlyConvertibleTo(*expected))
 			typeError(
@@ -590,7 +608,7 @@ bool TypeChecker::visit(VariableDeclarationStatement const& _statement)
 		VariableDeclaration const& varDecl = *_statement.declarations().front();
 		if (!varDecl.annotation().type)
 			fatalTypeError(_statement, "Assignment necessary for type detection.");
-		if (auto ref = dynamic_cast<ReferenceType const*>(varDecl.annotation().type.get()))
+		if (auto ref = dynamic_cast<ReferenceType const*>(type(varDecl).get()))
 		{
 			if (ref->dataStoredIn(DataLocation::Storage))
 			{
@@ -610,10 +628,10 @@ bool TypeChecker::visit(VariableDeclarationStatement const& _statement)
 
 	_statement.initialValue()->accept(*this);
 	TypePointers valueTypes;
-	if (auto tupleType = dynamic_cast<TupleType const*>(_statement.initialValue()->annotation().type.get()))
+	if (auto tupleType = dynamic_cast<TupleType const*>(type(*_statement.initialValue()).get()))
 		valueTypes = tupleType->components();
 	else
-		valueTypes = TypePointers{_statement.initialValue()->annotation().type};
+		valueTypes = TypePointers{type(*_statement.initialValue())};
 
 	// Determine which component is assigned to which variable.
 	// If numbers do not match, fill up if variables begin or end empty (not both).
@@ -712,7 +730,13 @@ bool TypeChecker::visit(Assignment const& _assignment)
 	requireLValue(_assignment.leftHandSide());
 	TypePointer t = type(_assignment.leftHandSide());
 	_assignment.annotation().type = t;
-	if (t->category() == Type::Category::Mapping)
+	if (TupleType const* tupleType = dynamic_cast<TupleType const*>(t.get()))
+	{
+		// Sequenced assignments of tuples is not valid, make the result a "void" type.
+		_assignment.annotation().type = make_shared<TupleType>();
+		expectType(_assignment.rightHandSide(), *tupleType);
+	}
+	else if (t->category() == Type::Category::Mapping)
 	{
 		typeError(_assignment, "Mappings cannot be assigned to.");
 		_assignment.rightHandSide().accept(*this);
@@ -741,6 +765,51 @@ bool TypeChecker::visit(Assignment const& _assignment)
 	return false;
 }
 
+bool TypeChecker::visit(TupleExpression const& _tuple)
+{
+	vector<ASTPointer<Expression>> const& components = _tuple.components();
+	TypePointers types;
+	if (_tuple.annotation().lValueRequested)
+	{
+		for (auto const& component: components)
+			if (component)
+			{
+				requireLValue(*component);
+				types.push_back(type(*component));
+			}
+			else
+				types.push_back(TypePointer());
+		_tuple.annotation().type = make_shared<TupleType>(types);
+		// If some of the components are not LValues, the error is reported above.
+		_tuple.annotation().isLValue = true;
+	}
+	else
+	{
+		for (size_t i = 0; i < components.size(); ++i)
+		{
+			// Outside of an lvalue-context, the only situation where a component can be empty is (x,).
+			if (!components[i] && !(i == 1 && components.size() == 2))
+				fatalTypeError(_tuple, "Tuple component cannot be empty.");
+			else if (components[i])
+			{
+				components[i]->accept(*this);
+				types.push_back(type(*components[i]));
+			}
+			else
+				types.push_back(TypePointer());
+		}
+		if (components.size() == 1)
+			_tuple.annotation().type = type(*components[0]);
+		else
+		{
+			if (components.size() == 2 && !components[1])
+				types.pop_back();
+			_tuple.annotation().type = make_shared<TupleType>(types);
+		}
+	}
+	return false;
+}
+
 bool TypeChecker::visit(UnaryOperation const& _operation)
 {
 	// Inc, Dec, Add, Sub, Not, BitNot, Delete
@@ -1236,10 +1305,10 @@ void TypeChecker::expectType(Expression const& _expression, Type const& _expecte
 
 void TypeChecker::requireLValue(Expression const& _expression)
 {
+	_expression.annotation().lValueRequested = true;
 	_expression.accept(*this);
 	if (!_expression.annotation().isLValue)
 		typeError(_expression, "Expression has to be an lvalue.");
-	_expression.annotation().lValueRequested = true;
 }
 
 void TypeChecker::typeError(ASTNode const& _node, string const& _description)
diff --git a/libsolidity/TypeChecker.h b/libsolidity/TypeChecker.h
index d9cb39ae..7af5473b 100644
--- a/libsolidity/TypeChecker.h
+++ b/libsolidity/TypeChecker.h
@@ -90,6 +90,7 @@ private:
 	virtual bool visit(VariableDeclarationStatement const& _variable) override;
 	virtual void endVisit(ExpressionStatement const& _statement) override;
 	virtual bool visit(Assignment const& _assignment) override;
+	virtual bool visit(TupleExpression const& _tuple) override;
 	virtual void endVisit(BinaryOperation const& _operation) override;
 	virtual bool visit(UnaryOperation const& _operation) override;
 	virtual bool visit(FunctionCall const& _functionCall) override;
diff --git a/libsolidity/Types.cpp b/libsolidity/Types.cpp
index 51df5fbf..02b86a7f 100644
--- a/libsolidity/Types.cpp
+++ b/libsolidity/Types.cpp
@@ -1242,6 +1242,38 @@ unsigned int EnumType::memberValue(ASTString const& _member) const
 	BOOST_THROW_EXCEPTION(m_enum.createTypeError("Requested unknown enum value ." + _member));
 }
 
+bool TupleType::isImplicitlyConvertibleTo(Type const& _other) const
+{
+	if (auto tupleType = dynamic_cast<TupleType const*>(&_other))
+	{
+		TypePointers const& targets = tupleType->components();
+		if (targets.empty())
+			return components().empty();
+		if (components().size() != targets.size() && !targets.front() && !targets.back())
+			return false; // (,a,) = (1,2,3,4) - unable to position `a` in the tuple.
+		size_t minNumValues = targets.size();
+		if (!targets.back() || !targets.front())
+			--minNumValues; // wildcards can also match 0 components
+		if (components().size() < minNumValues)
+			return false;
+		if (components().size() > targets.size() && targets.front() && targets.back())
+			return false; // larger source and no wildcard
+		bool fillRight = !targets.back() || targets.front();
+		for (size_t i = 0; i < min(targets.size(), components().size()); ++i)
+		{
+			auto const& s = components()[fillRight ? i : components().size() - i - 1];
+			auto const& t = targets[fillRight ? i : targets.size() - i - 1];
+			if (!s && t)
+				return false;
+			else if (s && t && !s->isImplicitlyConvertibleTo(*t))
+				return false;
+		}
+		return true;
+	}
+	else
+		return false;
+}
+
 bool TupleType::operator==(Type const& _other) const
 {
 	if (auto tupleType = dynamic_cast<TupleType const*>(&_other))
@@ -1252,12 +1284,12 @@ bool TupleType::operator==(Type const& _other) const
 
 string TupleType::toString(bool _short) const
 {
-	if (m_components.empty())
+	if (components().empty())
 		return "tuple()";
 	string str = "tuple(";
-	for (auto const& t: m_components)
-		str += t->toString(_short) + ", ";
-	str.resize(str.size() - 2);
+	for (auto const& t: components())
+		str += (t ? t->toString(_short) : "") + ",";
+	str.pop_back();
 	return str + ")";
 }
 
@@ -1272,11 +1304,35 @@ u256 TupleType::storageSize() const
 unsigned TupleType::sizeOnStack() const
 {
 	unsigned size = 0;
-	for (auto const& t: m_components)
-		size += t->sizeOnStack();
+	for (auto const& t: components())
+		size += t ? t->sizeOnStack() : 0;
 	return size;
 }
 
+TypePointer TupleType::mobileType() const
+{
+	TypePointers mobiles;
+	for (auto const& c: components())
+		mobiles.push_back(c ? c->mobileType() : TypePointer());
+	return make_shared<TupleType>(mobiles);
+}
+
+TypePointer TupleType::closestTemporaryType(TypePointer const& _targetType) const
+{
+	solAssert(!!_targetType, "");
+	TypePointers const& targetComponents = dynamic_cast<TupleType const&>(*_targetType).components();
+	bool fillRight = !targetComponents.empty() && (!targetComponents.back() || targetComponents.front());
+	TypePointers tempComponents(targetComponents.size());
+	for (size_t i = 0; i < min(targetComponents.size(), components().size()); ++i)
+	{
+		size_t si = fillRight ? i : components().size() - i - 1;
+		size_t ti = fillRight ? i : targetComponents.size() - i - 1;
+		if (components()[si] && targetComponents[ti])
+			tempComponents[ti] = components()[si]->closestTemporaryType(targetComponents[ti]);
+	}
+	return make_shared<TupleType>(tempComponents);
+}
+
 FunctionType::FunctionType(FunctionDefinition const& _function, bool _isInternal):
 	m_location(_isInternal ? Location::Internal : Location::External),
 	m_isConstant(_function.isDeclaredConst()),
@@ -1638,14 +1694,15 @@ FunctionTypePointer FunctionType::asMemberFunction(bool _inLibrary) const
 			parameterTypes.push_back(t);
 	}
 
-	//@todo make this more intelligent once we support destructuring assignments
+	// Removes dynamic types.
 	TypePointers returnParameterTypes;
 	vector<string> returnParameterNames;
-	if (!m_returnParameterTypes.empty() && m_returnParameterTypes.front()->calldataEncodedSize() > 0)
-	{
-		returnParameterTypes.push_back(m_returnParameterTypes.front());
-		returnParameterNames.push_back(m_returnParameterNames.front());
-	}
+	for (size_t i = 0; i < m_returnParameterTypes.size(); ++i)
+		if (m_returnParameterTypes[i]->calldataEncodedSize() > 0)
+		{
+			returnParameterTypes.push_back(m_returnParameterTypes[i]);
+			returnParameterNames.push_back(m_returnParameterNames[i]);
+		}
 	return make_shared<FunctionType>(
 		parameterTypes,
 		returnParameterTypes,
diff --git a/libsolidity/Types.h b/libsolidity/Types.h
index 5c4aacdc..626ebbe4 100644
--- a/libsolidity/Types.h
+++ b/libsolidity/Types.h
@@ -210,6 +210,13 @@ public:
 	/// @returns true if this is a non-value type and the data of this type is stored at the
 	/// given location.
 	virtual bool dataStoredIn(DataLocation) const { return false; }
+	/// @returns the type of a temporary during assignment to a variable of the given type.
+	/// Specifically, returns the requested itself if it can be dynamically allocated (or is a value type)
+	/// and the mobile type otherwise.
+	virtual TypePointer closestTemporaryType(TypePointer const& _targetType) const
+	{
+		return _targetType->dataStoredIn(DataLocation::Storage) ? mobileType() : _targetType;
+	}
 
 	/// Returns the list of all members of this type. Default implementation: no members.
 	virtual MemberList const& members() const { return EmptyMemberList; }
@@ -682,12 +689,14 @@ private:
 
 /**
  * Type that can hold a finite sequence of values of different types.
+ * In some cases, the components are empty pointers (when used as placeholders).
  */
 class TupleType: public Type
 {
 public:
 	virtual Category category() const override { return Category::Tuple; }
 	explicit TupleType(std::vector<TypePointer> const& _types = std::vector<TypePointer>()): m_components(_types) {}
+	virtual bool isImplicitlyConvertibleTo(Type const& _other) const override;
 	virtual bool operator==(Type const& _other) const override;
 	virtual TypePointer binaryOperatorResult(Token::Value, TypePointer const&) const override { return TypePointer(); }
 	virtual std::string toString(bool) const override;
@@ -695,6 +704,9 @@ public:
 	virtual u256 storageSize() const override;
 	virtual bool canLiveOutsideStorage() const override { return false; }
 	virtual unsigned sizeOnStack() const override;
+	virtual TypePointer mobileType() const override;
+	/// Converts components to their temporary types and performs some wildcard matching.
+	virtual TypePointer closestTemporaryType(TypePointer const& _targetType) const override;
 
 	std::vector<TypePointer> const& components() const { return m_components; }