From 3327981108fb0b3926336684c4c7d395ab5c0928 Mon Sep 17 00:00:00 2001 From: chriseth Date: Wed, 19 Sep 2018 14:35:12 +0200 Subject: More types. --- docs/types.rst | 54 ++++++++++++++++++++++++++++++++---------------------- 1 file changed, 32 insertions(+), 22 deletions(-) (limited to 'docs') diff --git a/docs/types.rst b/docs/types.rst index de384e2f..432420d3 100644 --- a/docs/types.rst +++ b/docs/types.rst @@ -259,15 +259,19 @@ Contract Types -------------- Every :ref:`contract` defines its own type. -You can implicitly convert contracts to contracts they inherit from, -and explicitly convert them to and from the ``address`` type, if they have no -payable fallback functions, or to and from the ``address payable`` type, if they do -have payable fallback functions. +You can implicitly convert contracts to contracts they inherit from. +Contracts can be explicitly converted to and from all other contract types +and the ``address`` type. + +Explicit conversion to and from the ``address payable`` type +is only possible if the contract type has a payable fallback function. +The conversion is still performed using ``address(x)`` and not +using ``address payable(x)``. You can find more information in the section about +the :ref:`address type
`. .. note:: - Starting with version 0.5.0 contracts do not derive from the address type, - but can still be explicitly converted to ``address``, resp. to ``address payable``, - if they have a payable fallback function. + Before version 0.5.0, contracts directly derived from the address type + and there was no distinction between ``address`` and ``address payable``. If you declare a local variable of contract type (`MyContract c`), you can call functions on that contract. Take care to assign it from somewhere that is the @@ -290,25 +294,29 @@ including public state variables. Fixed-size byte arrays ---------------------- -``bytes1``, ``bytes2``, ``bytes3``, ..., ``bytes32``. ``byte`` is an alias for ``bytes1``. +The value types ``bytes1``, ``bytes2``, ``bytes3``, ..., ``bytes32`` +hold a sequence of bytes from one to up to 32. +``byte`` is an alias for ``bytes1``. Operators: * Comparisons: ``<=``, ``<``, ``==``, ``!=``, ``>=``, ``>`` (evaluate to ``bool``) -* Bit operators: ``&``, ``|``, ``^`` (bitwise exclusive or), ``~`` (bitwise negation), ``<<`` (left shift), ``>>`` (right shift) +* Bit operators: ``&``, ``|``, ``^`` (bitwise exclusive or), ``~`` (bitwise negation) +* Shift operators: ``<<`` (left shift), ``>>`` (right shift) * Index access: If ``x`` is of type ``bytesI``, then ``x[k]`` for ``0 <= k < I`` returns the ``k`` th byte (read-only). -The shifting operator works with any integer type as right operand (but will -return the type of the left operand), which denotes the number of bits to shift by. -Shifting by a negative amount will cause a runtime exception. +The shifting operator works with any integer type as right operand (but +returns the type of the left operand), which denotes the number of bits to shift by. +Shifting by a negative amount causes a runtime exception. Members: * ``.length`` yields the fixed length of the byte array (read-only). .. note:: - It is possible to use an array of bytes as ``byte[]``, but it is wasting a lot of space, 31 bytes every element, - to be exact, when passing in calls. It is better to use ``bytes``. + The type ``byte[]`` is an array of bytes, but due to padding rules, it wastes + 31 bytes of space for each element (except in storage). It is better to use the ``bytes`` + type instead. Dynamically-sized byte array ---------------------------- @@ -326,7 +334,7 @@ Address Literals ---------------- Hexadecimal literals that pass the address checksum test, for example -``0xdCad3a6d3569DF655070DEd06cb7A1b2Ccd1D3AF`` are of ``address`` type. +``0xdCad3a6d3569DF655070DEd06cb7A1b2Ccd1D3AF`` are of ``address payable`` type. Hexadecimal literals that are between 39 and 41 digits long and do not pass the checksum test produce a warning and are treated as regular rational number literals. @@ -354,10 +362,11 @@ Examples include ``2e10``, ``-2e10``, ``2e-10``, ``2.5e1``. Underscores can be used to separate the digits of a numeric literal to aid readability. For example, decimal ``123_000``, hexadecimal ``0x2eff_abde``, scientific decimal notation ``1_2e345_678`` are all valid. Underscores are only allowed between two digits and only one consecutive underscore is allowed. -There is no additional semantic meaning added to a number literal containing underscores. +There is no additional semantic meaning added to a number literal containing underscores, +the underscores are ignored. 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). +using them together with a non-literal expression or by explicit conversion). This means that computations do not overflow and divisions do not truncate in number literal expressions. @@ -379,14 +388,15 @@ a non-rational number). belong to the same number literal type for the rational number three. .. warning:: - 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``. + Division on integer literals used to truncate in Solidity prior to version 0.4.0, but it now converts into a rational number, i.e. ``5 / 2`` is not equal to ``2``, but to ``2.5``. .. note:: 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, but the partial expression ``2.5 + a`` does not type check so the code - does not compile + expressions. Disregarding types, the value of the expression assigned to ``b`` + below evaluates to an integer. Because ``a`` is of type ``uint128``, the + expression ``2.5 + a`` has to have a proper type, though. Since there is no common type + for the type of ``2.5`` and ``uint128``, the Solidity compiler does not accept + this code. :: -- cgit v1.2.3