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author | Chris Ward <chris.ward@ethereum.org> | 2019-01-09 19:37:20 +0800 |
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committer | Chris Ward <chris.ward@ethereum.org> | 2019-01-09 19:37:20 +0800 |
commit | 4cc102fa61116036e0d7c811f081deecbaaf7cba (patch) | |
tree | 8be8092925ca7e98c13eaa92b26a5efee8d321f4 /docs/types.rst | |
parent | 60d836424f987ac7bf05673242618e5794379646 (diff) | |
download | dexon-solidity-4cc102fa61116036e0d7c811f081deecbaaf7cba.tar.gz dexon-solidity-4cc102fa61116036e0d7c811f081deecbaaf7cba.tar.zst dexon-solidity-4cc102fa61116036e0d7c811f081deecbaaf7cba.zip |
Split operators involving LValues into new doc
Diffstat (limited to 'docs/types.rst')
-rw-r--r-- | docs/types.rst | 48 |
1 files changed, 1 insertions, 47 deletions
diff --git a/docs/types.rst b/docs/types.rst index 4eb1f926..61b0afc0 100644 --- a/docs/types.rst +++ b/docs/types.rst @@ -1196,53 +1196,7 @@ each ``_KeyType``, recursively. For example with a mapping: Mappings are not iterable, but it is possible to implement a data structure on top of them. For an example, see `iterable mapping <https://github.com/ethereum/dapp-bin/blob/master/library/iterable_mapping.sol>`_. -.. index:: assignment, ! delete, lvalue - -Operators Involving LValues -=========================== - -If ``a`` is an LValue (i.e. a variable or something that can be assigned to), the following operators are available as shorthands: - -``a += e`` is equivalent to ``a = a + e``. The operators ``-=``, ``*=``, ``/=``, ``%=``, ``|=``, ``&=`` and ``^=`` are defined accordingly. ``a++`` and ``a--`` are equivalent to ``a += 1`` / ``a -= 1`` but the expression itself still has the previous value of ``a``. In contrast, ``--a`` and ``++a`` have the same effect on ``a`` but return the value after the change. - -delete ------- - -``delete a`` assigns the initial value for the type to ``a``. I.e. for integers it is -equivalent to ``a = 0``, but it can also be used on arrays, where it assigns a dynamic -array of length zero or a static array of the same length with all elements set to their -initial value. ``delete a[x]`` deletes the item at index ``x`` of the array and leaves -all other elements and the length of the array untouched. This especially means that it leaves -a gap in the array. If you plan to remove items, a mapping is probably a better choice. - -For structs, it assigns a struct with all members reset. In other words, the value of ``a`` after ``delete a`` is the same as if ``a`` would be declared without assignment, with the following caveat: - -``delete`` has no effect on mappings (as the keys of mappings may be arbitrary and are generally unknown). So if you delete a struct, it will reset all members that are not mappings and also recurse into the members unless they are mappings. However, individual keys and what they map to can be deleted: If ``a`` is a mapping, then ``delete a[x]`` will delete the value stored at ``x``. - -It is important to note that ``delete a`` really behaves like an assignment to ``a``, i.e. it stores a new object in ``a``. -This distinction is visible when ``a`` is reference variable: It will only reset ``a`` itself, not the -value it referred to previously. - -:: - - pragma solidity >=0.4.0 <0.6.0; - - contract DeleteExample { - uint data; - uint[] dataArray; - - function f() public { - uint x = data; - delete x; // sets x to 0, does not affect data - delete data; // sets data to 0, does not affect x - uint[] storage y = dataArray; - delete dataArray; // this sets dataArray.length to zero, but as uint[] is a complex object, also - // y is affected which is an alias to the storage object - // On the other hand: "delete y" is not valid, as assignments to local variables - // referencing storage objects can only be made from existing storage objects. - assert(y.length == 0); - } - } +.. include:: types/operators.rst .. index:: ! type;conversion, ! cast |