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Diffstat (limited to 'docs/control-structures.rst')
| -rw-r--r-- | docs/control-structures.rst | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/docs/control-structures.rst b/docs/control-structures.rst index 128e6fae..796e9238 100644 --- a/docs/control-structures.rst +++ b/docs/control-structures.rst @@ -381,13 +381,11 @@ Error handling: Assert, Require, Revert and Exceptions Solidity uses state-reverting exceptions to handle errors. Such an exception will undo all changes made to the state in the current call (and all its sub-calls) and also flag an error to the caller. The convenience functions ``assert`` and ``require`` can be used to check for conditions and throw an exception -if the condition is not met. The difference between the two is that ``assert`` should only be used for internal errors -and ``require`` should be used to check external conditions (invalid inputs or errors in external components). -The idea behind that is that analysis tools can check your contract and try to come up with situations and -series of function calls that will reach a failing assertion. If this is possible, this means there is a bug -in your contract you should fix. +if the condition is not met. The ``assert`` function should only be used to test for internal errors, and to check invariants. +The ``require`` function should be used to ensure valid conditions, such as inputs, or contract state variables are met, or to validate return values from calls to external contracts. +If used properly, analysis tools can evaluate your contract to identify the conditions and function calls which will reach a failing ``assert``. Properly functioning code should never reach a failing assert statement; if this happens there is a bug in your contract which you should fix. -There are two other ways to trigger execptions: The ``revert`` function can be used to flag an error and +There are two other ways to trigger exceptions: The ``revert`` function can be used to flag an error and revert the current call. In the future it might be possible to also include details about the error in a call to ``revert``. The ``throw`` keyword can also be used as an alternative to ``revert()``. @@ -395,6 +393,9 @@ When exceptions happen in a sub-call, they "bubble up" (i.e. exceptions are reth and the low-level functions ``call``, ``delegatecall`` and ``callcode`` -- those return ``false`` in case of an exception instead of "bubbling up". +.. warning:: + The low-level ``call``, ``delegatecall`` and ``callcode`` will return success if the calling account is non-existent, as part of the design of EVM. Existence must be checked prior to calling if desired. + Catching exceptions is not yet possible. In the following example, you can see how ``require`` can be used to easily check conditions on inputs |