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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:: .. note::
Prior to version 0.5.0, the compiler did not use the ``STATICCALL`` opcode Prior to version 0.5.0, the compiler did not use the ``STATICCALL`` opcode
for ``pure`` functions. 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 By using ``STATICCALL`` for ``pure`` functions, modifications to the
state are prevented on the level of the EVM. state are prevented on the level of the EVM.
.. warning:: .. note::
It is not possible to prevent functions from reading the state at the level Prior to version 0.4.17 the compiler did not enforce that ``pure`` is not reading the state.
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.
It is a compile-time type check, which can be circumvented doing invalid explicit conversions 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 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 not do state-changing operations, but it cannot check that the contract that will be called