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diff --git a/docs/yul.rst b/docs/yul.rst new file mode 100644 index 00000000..4f5ef98f --- /dev/null +++ b/docs/yul.rst @@ -0,0 +1,593 @@ +### +Yul +### + +.. _yul: + +.. index:: ! assembly, ! asm, ! evmasm, ! yul, julia, iulia + +Yul (previously also called JULIA or IULIA) is an intermediate language that can +compile to various different backends +(EVM 1.0, EVM 1.5 and eWASM are planned). +Because of that, it is designed to be a usable common denominator of all three +platforms. +It can already be used for "inline assembly" inside Solidity and +future versions of the Solidity compiler will even use Yul as intermediate +language. It should also be easy to build high-level optimizer stages for Yul. + +.. note:: + + Note that the flavour used for "inline assembly" does not have types + (everything is ``u256``) and the built-in functions are identical + to the EVM opcodes. Please resort to the inline assembly documentation + for details. + +The core components of Yul are functions, blocks, variables, literals, +for-loops, if-statements, switch-statements, expressions and assignments to variables. + +Yul is typed, both variables and literals must specify the type with postfix +notation. The supported types are ``bool``, ``u8``, ``s8``, ``u32``, ``s32``, +``u64``, ``s64``, ``u128``, ``s128``, ``u256`` and ``s256``. + +Yul in itself does not even provide operators. If the EVM is targeted, +opcodes will be available as built-in functions, but they can be reimplemented +if the backend changes. For a list of mandatory built-in functions, see the section below. + +The following example program assumes that the EVM opcodes ``mul``, ``div`` +and ``mod`` are available either natively or as functions and computes exponentiation. + +.. code:: + + { + function power(base:u256, exponent:u256) -> result:u256 + { + switch exponent + case 0:u256 { result := 1:u256 } + case 1:u256 { result := base } + default: + { + result := power(mul(base, base), div(exponent, 2:u256)) + switch mod(exponent, 2:u256) + case 1:u256 { result := mul(base, result) } + } + } + } + +It is also possible to implement the same function using a for-loop +instead of with recursion. Here, we need the EVM opcodes ``lt`` (less-than) +and ``add`` to be available. + +.. code:: + + { + function power(base:u256, exponent:u256) -> result:u256 + { + result := 1:u256 + for { let i := 0:u256 } lt(i, exponent) { i := add(i, 1:u256) } + { + result := mul(result, base) + } + } + } + +Specification of Yul +==================== + +This chapter describes Yul code. It is usually placed inside a Yul object, which is described in the following chapter. + +Grammar:: + + Block = '{' Statement* '}' + Statement = + Block | + FunctionDefinition | + VariableDeclaration | + Assignment | + Expression | + Switch | + ForLoop | + BreakContinue + FunctionDefinition = + 'function' Identifier '(' TypedIdentifierList? ')' + ( '->' TypedIdentifierList )? Block + VariableDeclaration = + 'let' TypedIdentifierList ( ':=' Expression )? + Assignment = + IdentifierList ':=' Expression + Expression = + FunctionCall | Identifier | Literal + If = + 'if' Expression Block + Switch = + 'switch' Expression Case* ( 'default' Block )? + Case = + 'case' Literal Block + ForLoop = + 'for' Block Expression Block Block + BreakContinue = + 'break' | 'continue' + FunctionCall = + Identifier '(' ( Expression ( ',' Expression )* )? ')' + Identifier = [a-zA-Z_$] [a-zA-Z_0-9]* + IdentifierList = Identifier ( ',' Identifier)* + TypeName = Identifier | BuiltinTypeName + BuiltinTypeName = 'bool' | [us] ( '8' | '32' | '64' | '128' | '256' ) + TypedIdentifierList = Identifier ':' TypeName ( ',' Identifier ':' TypeName )* + Literal = + (NumberLiteral | StringLiteral | HexLiteral | TrueLiteral | FalseLiteral) ':' TypeName + NumberLiteral = HexNumber | DecimalNumber + HexLiteral = 'hex' ('"' ([0-9a-fA-F]{2})* '"' | '\'' ([0-9a-fA-F]{2})* '\'') + StringLiteral = '"' ([^"\r\n\\] | '\\' .)* '"' + TrueLiteral = 'true' + FalseLiteral = 'false' + HexNumber = '0x' [0-9a-fA-F]+ + DecimalNumber = [0-9]+ + +Restrictions on the Grammar +--------------------------- + +Switches must have at least one case (including the default case). +If all possible values of the expression is covered, the default case should +not be allowed (i.e. a switch with a ``bool`` expression and having both a +true and false case should not allow a default case). + +Every expression evaluates to zero or more values. Identifiers and Literals +evaluate to exactly +one value and function calls evaluate to a number of values equal to the +number of return values of the function called. + +In variable declarations and assignments, the right-hand-side expression +(if present) has to evaluate to a number of values equal to the number of +variables on the left-hand-side. +This is the only situation where an expression evaluating +to more than one value is allowed. + +Expressions that are also statements (i.e. at the block level) have to +evaluate to zero values. + +In all other situations, expressions have to evaluate to exactly one value. + +The ``continue`` and ``break`` statements can only be used inside loop bodies +and have to be in the same function as the loop (or both have to be at the +top level). +The condition part of the for-loop has to evaluate to exactly one value. + +Literals cannot be larger than the their type. The largest type defined is 256-bit wide. + +Scoping Rules +------------- + +Scopes in Yul are tied to Blocks (exceptions are functions and the for loop +as explained below) and all declarations +(``FunctionDefinition``, ``VariableDeclaration``) +introduce new identifiers into these scopes. + +Identifiers are visible in +the block they are defined in (including all sub-nodes and sub-blocks). +As an exception, identifiers defined in the "init" part of the for-loop +(the first block) are visible in all other parts of the for-loop +(but not outside of the loop). +Identifiers declared in the other parts of the for loop respect the regular +syntatical scoping rules. +The parameters and return parameters of functions are visible in the +function body and their names cannot overlap. + +Variables can only be referenced after their declaration. In particular, +variables cannot be referenced in the right hand side of their own variable +declaration. +Functions can be referenced already before their declaration (if they are visible). + +Shadowing is disallowed, i.e. you cannot declare an identifier at a point +where another identifier with the same name is also visible, even if it is +not accessible. + +Inside functions, it is not possible to access a variable that was declared +outside of that function. + +Formal Specification +-------------------- + +We formally specify Yul by providing an evaluation function E overloaded +on the various nodes of the AST. Any functions can have side effects, so +E takes two state objects and the AST node and returns two new +state objects and a variable number of other values. +The two state objects are the global state object +(which in the context of the EVM is the memory, storage and state of the +blockchain) and the local state object (the state of local variables, i.e. a +segment of the stack in the EVM). +If the AST node is a statement, E returns the two state objects and a "mode", +which is used for the ``break`` and ``continue`` statements. +If the AST node is an expression, E returns the two state objects and +as many values as the expression evaluates to. + + +The exact nature of the global state is unspecified for this high level +description. The local state ``L`` is a mapping of identifiers ``i`` to values ``v``, +denoted as ``L[i] = v``. + +For an identifier ``v``, let ``$v`` be the name of the identifier. + +We will use a destructuring notation for the AST nodes. + +.. code:: + + E(G, L, <{St1, ..., Stn}>: Block) = + let G1, L1, mode = E(G, L, St1, ..., Stn) + let L2 be a restriction of L1 to the identifiers of L + G1, L2, mode + E(G, L, St1, ..., Stn: Statement) = + if n is zero: + G, L, regular + else: + let G1, L1, mode = E(G, L, St1) + if mode is regular then + E(G1, L1, St2, ..., Stn) + otherwise + G1, L1, mode + E(G, L, FunctionDefinition) = + G, L, regular + E(G, L, <let var1, ..., varn := rhs>: VariableDeclaration) = + E(G, L, <var1, ..., varn := rhs>: Assignment) + E(G, L, <let var1, ..., varn>: VariableDeclaration) = + let L1 be a copy of L where L1[$vari] = 0 for i = 1, ..., n + G, L1, regular + E(G, L, <var1, ..., varn := rhs>: Assignment) = + let G1, L1, v1, ..., vn = E(G, L, rhs) + let L2 be a copy of L1 where L2[$vari] = vi for i = 1, ..., n + G, L2, regular + E(G, L, <for { i1, ..., in } condition post body>: ForLoop) = + if n >= 1: + let G1, L1, mode = E(G, L, i1, ..., in) + // mode has to be regular due to the syntactic restrictions + let G2, L2, mode = E(G1, L1, for {} condition post body) + // mode has to be regular due to the syntactic restrictions + let L3 be the restriction of L2 to only variables of L + G2, L3, regular + else: + let G1, L1, v = E(G, L, condition) + if v is false: + G1, L1, regular + else: + let G2, L2, mode = E(G1, L, body) + if mode is break: + G2, L2, regular + else: + G3, L3, mode = E(G2, L2, post) + E(G3, L3, for {} condition post body) + E(G, L, break: BreakContinue) = + G, L, break + E(G, L, continue: BreakContinue) = + G, L, continue + E(G, L, <if condition body>: If) = + let G0, L0, v = E(G, L, condition) + if v is true: + E(G0, L0, body) + else: + G0, L0, regular + E(G, L, <switch condition case l1:t1 st1 ... case ln:tn stn>: Switch) = + E(G, L, switch condition case l1:t1 st1 ... case ln:tn stn default {}) + E(G, L, <switch condition case l1:t1 st1 ... case ln:tn stn default st'>: Switch) = + let G0, L0, v = E(G, L, condition) + // i = 1 .. n + // Evaluate literals, context doesn't matter + let _, _, v1 = E(G0, L0, l1) + ... + let _, _, vn = E(G0, L0, ln) + if there exists smallest i such that vi = v: + E(G0, L0, sti) + else: + E(G0, L0, st') + + E(G, L, <name>: Identifier) = + G, L, L[$name] + E(G, L, <fname(arg1, ..., argn)>: FunctionCall) = + G1, L1, vn = E(G, L, argn) + ... + G(n-1), L(n-1), v2 = E(G(n-2), L(n-2), arg2) + Gn, Ln, v1 = E(G(n-1), L(n-1), arg1) + Let <function fname (param1, ..., paramn) -> ret1, ..., retm block> + be the function of name $fname visible at the point of the call. + Let L' be a new local state such that + L'[$parami] = vi and L'[$reti] = 0 for all i. + Let G'', L'', mode = E(Gn, L', block) + G'', Ln, L''[$ret1], ..., L''[$retm] + E(G, L, l: HexLiteral) = G, L, hexString(l), + where hexString decodes l from hex and left-aligns it into 32 bytes + E(G, L, l: StringLiteral) = G, L, utf8EncodeLeftAligned(l), + where utf8EncodeLeftAligned performs a utf8 encoding of l + and aligns it left into 32 bytes + E(G, L, n: HexNumber) = G, L, hex(n) + where hex is the hexadecimal decoding function + E(G, L, n: DecimalNumber) = G, L, dec(n), + where dec is the decimal decoding function + +Type Conversion Functions +------------------------- + +Yul has no support for implicit type conversion and therefore functions exist to provide explicit conversion. +When converting a larger type to a shorter type a runtime exception can occur in case of an overflow. + +Truncating conversions are supported between the following types: + - ``bool`` + - ``u32`` + - ``u64`` + - ``u256`` + - ``s256`` + +For each of these a type conversion function exists having the prototype in the form of ``<input_type>to<output_type>(x:<input_type>) -> y:<output_type>``, +such as ``u32tobool(x:u32) -> y:bool``, ``u256tou32(x:u256) -> y:u32`` or ``s256tou256(x:s256) -> y:u256``. + +.. note:: + + ``u32tobool(x:u32) -> y:bool`` can be implemented as ``y := not(iszerou256(x))`` and + ``booltou32(x:bool) -> y:u32`` can be implemented as ``switch x case true:bool { y := 1:u32 } case false:bool { y := 0:u32 }`` + +Low-level Functions +------------------- + +The following functions must be available: + ++---------------------------------------------------------------------------------------------------------------+ +| *Logic* | ++---------------------------------------------+-----------------------------------------------------------------+ +| not(x:bool) -> z:bool | logical not | ++---------------------------------------------+-----------------------------------------------------------------+ +| and(x:bool, y:bool) -> z:bool | logical and | ++---------------------------------------------+-----------------------------------------------------------------+ +| or(x:bool, y:bool) -> z:bool | logical or | ++---------------------------------------------+-----------------------------------------------------------------+ +| xor(x:bool, y:bool) -> z:bool | xor | ++---------------------------------------------+-----------------------------------------------------------------+ +| *Arithmetics* | ++---------------------------------------------+-----------------------------------------------------------------+ +| addu256(x:u256, y:u256) -> z:u256 | x + y | ++---------------------------------------------+-----------------------------------------------------------------+ +| subu256(x:u256, y:u256) -> z:u256 | x - y | ++---------------------------------------------+-----------------------------------------------------------------+ +| mulu256(x:u256, y:u256) -> z:u256 | x * y | ++---------------------------------------------+-----------------------------------------------------------------+ +| divu256(x:u256, y:u256) -> z:u256 | x / y | ++---------------------------------------------+-----------------------------------------------------------------+ +| divs256(x:s256, y:s256) -> z:s256 | x / y, for signed numbers in two's complement | ++---------------------------------------------+-----------------------------------------------------------------+ +| modu256(x:u256, y:u256) -> z:u256 | x % y | ++---------------------------------------------+-----------------------------------------------------------------+ +| mods256(x:s256, y:s256) -> z:s256 | x % y, for signed numbers in two's complement | ++---------------------------------------------+-----------------------------------------------------------------+ +| signextendu256(i:u256, x:u256) -> z:u256 | sign extend from (i*8+7)th bit counting from least significant | ++---------------------------------------------+-----------------------------------------------------------------+ +| expu256(x:u256, y:u256) -> z:u256 | x to the power of y | ++---------------------------------------------+-----------------------------------------------------------------+ +| addmodu256(x:u256, y:u256, m:u256) -> z:u256| (x + y) % m with arbitrary precision arithmetics | ++---------------------------------------------+-----------------------------------------------------------------+ +| mulmodu256(x:u256, y:u256, m:u256) -> z:u256| (x * y) % m with arbitrary precision arithmetics | ++---------------------------------------------+-----------------------------------------------------------------+ +| ltu256(x:u256, y:u256) -> z:bool | true if x < y, false otherwise | ++---------------------------------------------+-----------------------------------------------------------------+ +| gtu256(x:u256, y:u256) -> z:bool | true if x > y, false otherwise | ++---------------------------------------------+-----------------------------------------------------------------+ +| sltu256(x:s256, y:s256) -> z:bool | true if x < y, false otherwise | +| | (for signed numbers in two's complement) | ++---------------------------------------------+-----------------------------------------------------------------+ +| sgtu256(x:s256, y:s256) -> z:bool | true if x > y, false otherwise | +| | (for signed numbers in two's complement) | ++---------------------------------------------+-----------------------------------------------------------------+ +| equ256(x:u256, y:u256) -> z:bool | true if x == y, false otherwise | ++---------------------------------------------+-----------------------------------------------------------------+ +| iszerou256(x:u256) -> z:bool | true if x == 0, false otherwise | ++---------------------------------------------+-----------------------------------------------------------------+ +| notu256(x:u256) -> z:u256 | ~x, every bit of x is negated | ++---------------------------------------------+-----------------------------------------------------------------+ +| andu256(x:u256, y:u256) -> z:u256 | bitwise and of x and y | ++---------------------------------------------+-----------------------------------------------------------------+ +| oru256(x:u256, y:u256) -> z:u256 | bitwise or of x and y | ++---------------------------------------------+-----------------------------------------------------------------+ +| xoru256(x:u256, y:u256) -> z:u256 | bitwise xor of x and y | ++---------------------------------------------+-----------------------------------------------------------------+ +| shlu256(x:u256, y:u256) -> z:u256 | logical left shift of x by y | ++---------------------------------------------+-----------------------------------------------------------------+ +| shru256(x:u256, y:u256) -> z:u256 | logical right shift of x by y | ++---------------------------------------------+-----------------------------------------------------------------+ +| saru256(x:u256, y:u256) -> z:u256 | arithmetic right shift of x by y | ++---------------------------------------------+-----------------------------------------------------------------+ +| byte(n:u256, x:u256) -> v:u256 | nth byte of x, where the most significant byte is the 0th byte | +| | Cannot this be just replaced by and256(shr256(n, x), 0xff) and | +| | let it be optimised out by the EVM backend? | ++---------------------------------------------+-----------------------------------------------------------------+ +| *Memory and storage* | ++---------------------------------------------+-----------------------------------------------------------------+ +| mload(p:u256) -> v:u256 | mem[p..(p+32)) | ++---------------------------------------------+-----------------------------------------------------------------+ +| mstore(p:u256, v:u256) | mem[p..(p+32)) := v | ++---------------------------------------------+-----------------------------------------------------------------+ +| mstore8(p:u256, v:u256) | mem[p] := v & 0xff - only modifies a single byte | ++---------------------------------------------+-----------------------------------------------------------------+ +| sload(p:u256) -> v:u256 | storage[p] | ++---------------------------------------------+-----------------------------------------------------------------+ +| sstore(p:u256, v:u256) | storage[p] := v | ++---------------------------------------------+-----------------------------------------------------------------+ +| msize() -> size:u256 | size of memory, i.e. largest accessed memory index, albeit due | +| | due to the memory extension function, which extends by words, | +| | this will always be a multiple of 32 bytes | ++---------------------------------------------+-----------------------------------------------------------------+ +| *Execution control* | ++---------------------------------------------+-----------------------------------------------------------------+ +| create(v:u256, p:u256, s:u256) | create new contract with code mem[p..(p+s)) and send v wei | +| | and return the new address | ++---------------------------------------------+-----------------------------------------------------------------+ +| call(g:u256, a:u256, v:u256, in:u256, | call contract at address a with input mem[in..(in+insize)) | +| insize:u256, out:u256, | providing g gas and v wei and output area | +| outsize:u256) | mem[out..(out+outsize)) returning 0 on error (eg. out of gas) | +| -> r:u256 | and 1 on success | ++---------------------------------------------+-----------------------------------------------------------------+ +| callcode(g:u256, a:u256, v:u256, in:u256, | identical to ``call`` but only use the code from a | +| insize:u256, out:u256, | and stay in the context of the | +| outsize:u256) -> r:u256 | current contract otherwise | ++---------------------------------------------+-----------------------------------------------------------------+ +| delegatecall(g:u256, a:u256, in:u256, | identical to ``callcode``, | +| insize:u256, out:u256, | but also keep ``caller`` | +| outsize:u256) -> r:u256 | and ``callvalue`` | ++---------------------------------------------+-----------------------------------------------------------------+ +| abort() | abort (equals to invalid instruction on EVM) | ++---------------------------------------------+-----------------------------------------------------------------+ +| return(p:u256, s:u256) | end execution, return data mem[p..(p+s)) | ++---------------------------------------------+-----------------------------------------------------------------+ +| revert(p:u256, s:u256) | end execution, revert state changes, return data mem[p..(p+s)) | ++---------------------------------------------+-----------------------------------------------------------------+ +| selfdestruct(a:u256) | end execution, destroy current contract and send funds to a | ++---------------------------------------------+-----------------------------------------------------------------+ +| log0(p:u256, s:u256) | log without topics and data mem[p..(p+s)) | ++---------------------------------------------+-----------------------------------------------------------------+ +| log1(p:u256, s:u256, t1:u256) | log with topic t1 and data mem[p..(p+s)) | ++---------------------------------------------+-----------------------------------------------------------------+ +| log2(p:u256, s:u256, t1:u256, t2:u256) | log with topics t1, t2 and data mem[p..(p+s)) | ++---------------------------------------------+-----------------------------------------------------------------+ +| log3(p:u256, s:u256, t1:u256, t2:u256, | log with topics t, t2, t3 and data mem[p..(p+s)) | +| t3:u256) | | ++---------------------------------------------+-----------------------------------------------------------------+ +| log4(p:u256, s:u256, t1:u256, t2:u256, | log with topics t1, t2, t3, t4 and data mem[p..(p+s)) | +| t3:u256, t4:u256) | | ++---------------------------------------------+-----------------------------------------------------------------+ +| *State queries* | ++---------------------------------------------+-----------------------------------------------------------------+ +| blockcoinbase() -> address:u256 | current mining beneficiary | ++---------------------------------------------+-----------------------------------------------------------------+ +| blockdifficulty() -> difficulty:u256 | difficulty of the current block | ++---------------------------------------------+-----------------------------------------------------------------+ +| blockgaslimit() -> limit:u256 | block gas limit of the current block | ++---------------------------------------------+-----------------------------------------------------------------+ +| blockhash(b:u256) -> hash:u256 | hash of block nr b - only for last 256 blocks excluding current | ++---------------------------------------------+-----------------------------------------------------------------+ +| blocknumber() -> block:u256 | current block number | ++---------------------------------------------+-----------------------------------------------------------------+ +| blocktimestamp() -> timestamp:u256 | timestamp of the current block in seconds since the epoch | ++---------------------------------------------+-----------------------------------------------------------------+ +| txorigin() -> address:u256 | transaction sender | ++---------------------------------------------+-----------------------------------------------------------------+ +| txgasprice() -> price:u256 | gas price of the transaction | ++---------------------------------------------+-----------------------------------------------------------------+ +| gasleft() -> gas:u256 | gas still available to execution | ++---------------------------------------------+-----------------------------------------------------------------+ +| balance(a:u256) -> v:u256 | wei balance at address a | ++---------------------------------------------+-----------------------------------------------------------------+ +| this() -> address:u256 | address of the current contract / execution context | ++---------------------------------------------+-----------------------------------------------------------------+ +| caller() -> address:u256 | call sender (excluding delegatecall) | ++---------------------------------------------+-----------------------------------------------------------------+ +| callvalue() -> v:u256 | wei sent together with the current call | ++---------------------------------------------+-----------------------------------------------------------------+ +| calldataload(p:u256) -> v:u256 | call data starting from position p (32 bytes) | ++---------------------------------------------+-----------------------------------------------------------------+ +| calldatasize() -> v:u256 | size of call data in bytes | ++---------------------------------------------+-----------------------------------------------------------------+ +| calldatacopy(t:u256, f:u256, s:u256) | copy s bytes from calldata at position f to mem at position t | ++---------------------------------------------+-----------------------------------------------------------------+ +| codesize() -> size:u256 | size of the code of the current contract / execution context | ++---------------------------------------------+-----------------------------------------------------------------+ +| codecopy(t:u256, f:u256, s:u256) | copy s bytes from code at position f to mem at position t | ++---------------------------------------------+-----------------------------------------------------------------+ +| extcodesize(a:u256) -> size:u256 | size of the code at address a | ++---------------------------------------------+-----------------------------------------------------------------+ +| extcodecopy(a:u256, t:u256, f:u256, s:u256) | like codecopy(t, f, s) but take code at address a | ++---------------------------------------------+-----------------------------------------------------------------+ +| *Others* | ++---------------------------------------------+-----------------------------------------------------------------+ +| discard(unused:bool) | discard value | ++---------------------------------------------+-----------------------------------------------------------------+ +| discardu256(unused:u256) | discard value | ++---------------------------------------------+-----------------------------------------------------------------+ +| splitu256tou64(x:u256) -> (x1:u64, x2:u64, | split u256 to four u64's | +| x3:u64, x4:u64) | | ++---------------------------------------------+-----------------------------------------------------------------+ +| combineu64tou256(x1:u64, x2:u64, x3:u64, | combine four u64's into a single u256 | +| x4:u64) -> (x:u256) | | ++---------------------------------------------+-----------------------------------------------------------------+ +| keccak256(p:u256, s:u256) -> v:u256 | keccak(mem[p...(p+s))) | ++---------------------------------------------+-----------------------------------------------------------------+ + +Backends +-------- + +Backends or targets are the translators from Yul to a specific bytecode. Each of the backends can expose functions +prefixed with the name of the backend. We reserve ``evm_`` and ``ewasm_`` prefixes for the two proposed backends. + +Backend: EVM +------------ + +The EVM target will have all the underlying EVM opcodes exposed with the `evm_` prefix. + +Backend: "EVM 1.5" +------------------ + +TBD + +Backend: eWASM +-------------- + +TBD + +Specification of Yul Object +=========================== + +Grammar:: + + TopLevelObject = 'object' '{' Code? ( Object | Data )* '}' + Object = 'object' StringLiteral '{' Code? ( Object | Data )* '}' + Code = 'code' Block + Data = 'data' StringLiteral HexLiteral + HexLiteral = 'hex' ('"' ([0-9a-fA-F]{2})* '"' | '\'' ([0-9a-fA-F]{2})* '\'') + StringLiteral = '"' ([^"\r\n\\] | '\\' .)* '"' + +Above, ``Block`` refers to ``Block`` in the Yul code grammar explained in the previous chapter. + +An example Yul Object is shown below: + +.. code:: + + // Code consists of a single object. A single "code" node is the code of the object. + // Every (other) named object or data section is serialized and + // made accessible to the special built-in functions datacopy / dataoffset / datasize + object { + code { + let size = datasize("runtime") + let offset = allocate(size) + // This will turn into a memory->memory copy for eWASM and + // a codecopy for EVM + datacopy(dataoffset("runtime"), offset, size) + // this is a constructor and the runtime code is returned + return(offset, size) + } + + data "Table2" hex"4123" + + object "runtime" { + code { + // runtime code + + let size = datasize("Contract2") + let offset = allocate(size) + // This will turn into a memory->memory copy for eWASM and + // a codecopy for EVM + datacopy(dataoffset("Contract2"), offset, size) + // constructor parameter is a single number 0x1234 + mstore(add(offset, size), 0x1234) + create(offset, add(size, 32)) + } + + // Embedded object. Use case is that the outside is a factory contract, + // and Contract2 is the code to be created by the factory + object "Contract2" { + code { + // code here ... + } + + object "runtime" { + code { + // code here ... + } + } + + data "Table1" hex"4123" + } + } + } |