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Document modifier changes.

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chriseth 2020-12-03 16:21:21 +01:00
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docs/ir/ir-breaking-changes.rst
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@ -34,6 +34,27 @@ Consequently, if the padding space within a struct is used to store data (e.g. i
We have the same behavior for implicit delete, for example when array of structs is shortened.
* Function modifiers are implemented in a slightly different way regarding function parameters.
This especially has an effect if the placeholder ``_;`` is evaluated multiple times in a modifier.
In the old code generator, each function parameter has a fixed slot on the stack. If the function
is run multiple times because ``_;`` is used multiple times or used in a loop, then a change to the
function parameter's value is visible in the next execution of the function.
The new code generator implements modifiers using actual functions and passes function parameters on.
This means that multiple executions of a function will get the same values for the parameters.
::
// SPDX-License-Identifier: GPL-3.0
pragma solidity >=0.7.0;
contract C {
function f(uint a) public pure mod() returns (uint r) {
r = a++;
}
modifier mod() { _; _; }
}
If you execute ``f(0)`` in the old code generator, it will return ``2``, while
it will return ``1`` when using the new code generator.
* The order of contract initialization has changed in case of inheritance.
The order used to be: