diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/control-structures.rst | 64 | ||||
| -rw-r--r-- | docs/types.rst | 21 |
2 files changed, 77 insertions, 8 deletions
diff --git a/docs/control-structures.rst b/docs/control-structures.rst index f57e7936..974a093f 100644 --- a/docs/control-structures.rst +++ b/docs/control-structures.rst @@ -2,12 +2,62 @@ Expressions and Control Structures ################################## +.. index:: ! parameter, parameter;input, parameter;output + +Input Parameters and Output Parameters +====================================== + +As in Javascript, functions may take parameters as input; +unlike in Javascript and C, they may also return arbitrary number of +parameters as output. + +Input Parameters +---------------- + +The input parameters are declared the same way as variables are. As an +exception, unused parameters can omit the variable name. +For example, suppose we want our contract to +accept one kind of external calls with two integers, we would write +something like:: + + contract Simple { + function taker(uint _a, uint _b) { + // do something with _a and _b. + } + } + +Output Parameters +----------------- + +The output parameters can be declared with the same syntax after the +``returns`` keyword. For example, suppose we wished to return two results: +the sum and the product of the two given integers, then we would +write:: + + contract Simple { + function arithmetics(uint _a, uint _b) returns (uint o_sum, uint o_product) { + o_sum = _a + _b; + o_product = _a * _b; + } + } + +The names of output parameters can be omitted. +The output values can also be specified using ``return`` statements. +The ``return`` statements are also capable of returning multiple +values, see :ref:`multi-return`. +Return parameters are initialized to zero; if they are not explicitly +set, they stay to be zero. + +Input parameters and output parameters can be used as expressions in +the function body. There, they are also usable in the left-hand side +of assignment. + .. index:: if, else, while, do/while, for, break, continue, return, switch, goto Control Structures =================== -Most of the control structures from C or JavaScript are available in Solidity +Most of the control structures from JavaScript are available in Solidity except for ``switch`` and ``goto``. So there is: ``if``, ``else``, ``while``, ``do``, ``for``, ``break``, ``continue``, ``return``, ``? :``, with the usual semantics known from C or JavaScript. @@ -16,7 +66,17 @@ Parentheses can *not* be omitted for conditionals, but curly brances can be omit around single-statement bodies. Note that there is no type conversion from non-boolean to boolean types as -there is in C and JavaScript, so ``if (1) { ... }`` is *not* valid Solidity. +there is in C and JavaScript, so ``if (1) { ... }`` is *not* valid +Solidity. + +.. _multi-return: + +Returning Multiple Values +------------------------- + +When a function has multiple output parameters, ``return (v0, v1, ..., +vn)`` can return multiple values. The number of components must be +the same as the number of output parameters. .. index:: ! function;call, function;internal, function;external diff --git a/docs/types.rst b/docs/types.rst index 21575cfb..0436fc70 100644 --- a/docs/types.rst +++ b/docs/types.rst @@ -169,9 +169,10 @@ Fixed Point Numbers Rational and Integer Literals ----------------------------- -All number literals retain arbitrary precision until they are converted to a non-literal type (i.e. by -using them together with a non-literal type). This means that computations do not overflow but also -divisions do not truncate. +Number literal expressions retain arbitrary precision until they are converted to a non-literal type (i.e. by +using them together with a non-literal expression). +This means that computations do not overflow and divisions do not truncate +in number literal expressions. For example, ``(2**800 + 1) - 2**800`` results in the constant ``1`` (of type ``uint8``) although intermediate results would not even fit the machine word size. Furthermore, ``.5 * 8`` results @@ -185,12 +186,20 @@ In ``var x = 1/4;``, ``x`` will receive the type ``ufixed0x8`` while in ``var x the type ``ufixed0x256`` because ``1/3`` is not finitely representable in binary and will thus be approximated. -Any operator that can be applied to integers can also be applied to literal expressions as +Any operator that can be applied to integers can also be applied to number literal expressions as long as the operands are integers. If any of the two is fractional, bit operations are disallowed and exponentiation is disallowed if the exponent is fractional (because that might result in a non-rational number). .. note:: + Solidity has a number literal type for each rational number. + Integer literals and rational number literals belong to number literal types. + Moreover, all number literal expressions (i.e. the expressions that + contain only number literals and operators) belong to number literal + types. So the number literal expressions `1 + 2` and `2 + 1` both + belong to the same number literal type for the rational number three. + +.. note:: Most finite decimal fractions like ``5.3743`` are not finitely representable in binary. The correct type for ``5.3743`` is ``ufixed8x248`` because that allows to best approximate the number. If you want to use the number together with types like ``ufixed`` (i.e. ``ufixed128x128``), you have to explicitly @@ -200,7 +209,7 @@ a non-rational number). Division on integer literals used to truncate in earlier versions, but it will now convert into a rational number, i.e. ``5 / 2`` is not equal to ``2``, but to ``2.5``. .. note:: - Literal expressions are converted to a permanent type as soon as they are used with other + Number literal expressions are converted into a non-literal type as soon as they are used with non-literal expressions. Even though we know that the value of the expression assigned to ``b`` in the following example evaluates to an integer, it still uses fixed point types (and not rational number literals) in between and so the code @@ -216,7 +225,7 @@ a non-rational number). String Literals --------------- -String literals are written with either double or single-quotes (``"foo"`` or ``'bar'``). As with integer literals, their type can vary, but they are implicitly convertible to ``bytes1``, ..., ``bytes32``, if they fit, to ``bytes`` and to ``string``. +String literals are written with either double or single-quotes (``"foo"`` or ``'bar'``). They do not imply trailing zeroes as in C; `"foo"`` represents three bytes not four. As with integer literals, their type can vary, but they are implicitly convertible to ``bytes1``, ..., ``bytes32``, if they fit, to ``bytes`` and to ``string``. String literals support escape characters, such as ``\n``, ``\xNN`` and ``\uNNNN``. ``\xNN`` takes a hex value and inserts the appropriate byte, while ``\uNNNN`` takes a Unicode codepoint and inserts an UTF-8 sequence. |