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Merge pull request #5277 from ethereum/docs-5175-require-revert

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DOCS: Add mention that pure functions can require and revert
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chriseth 2018-11-26 20:10:12 +01:00 committed by GitHub
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docs/contracts.rst
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@ -671,6 +671,20 @@ In addition to the list of state modifying statements explained above, the follo
}
}
Pure functions are able to use the `revert()` and `require()` functions to revert
potential state changes when an :ref:`error occurs <assert-and-require>`.
Reverting a state change is not considered a "state modification", as only changes to the
state made previously in code that did not have the ``view`` or ``pure`` restriction
are reverted and that code has the option to catch the ``revert`` and not pass it on.
This behaviour is also in line with the ``STATICCALL`` opcode.
.. warning::
It is not possible to prevent functions from reading the state at the level
of the EVM, it is only possible to prevent them from writing to the state
(i.e. only ``view`` can be enforced at the EVM level, ``pure`` can not).
.. note::
Prior to version 0.5.0, the compiler did not use the ``STATICCALL`` opcode
for ``pure`` functions.
@ -679,13 +693,8 @@ In addition to the list of state modifying statements explained above, the follo
By using ``STATICCALL`` for ``pure`` functions, modifications to the
state are prevented on the level of the EVM.
.. warning::
It is not possible to prevent functions from reading the state at the level
of the EVM, it is only possible to prevent them from writing to the state
(i.e. only ``view`` can be enforced at the EVM level, ``pure`` can not).
.. warning::
Before version 0.4.17 the compiler did not enforce that ``pure`` is not reading the state.
.. note::
Prior to version 0.4.17 the compiler did not enforce that ``pure`` is not reading the state.
It is a compile-time type check, which can be circumvented doing invalid explicit conversions
between contract types, because the compiler can verify that the type of the contract does
not do state-changing operations, but it cannot check that the contract that will be called