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Clarify forwarding of error data.

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chriseth 2020-11-19 10:49:40 +01:00
parent a0a02f2307
commit b1cfb5506d
1 changed files with 13 additions and 7 deletions
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docs/control-structures.rst
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@ -562,7 +562,7 @@ of an exception instead of "bubbling up".
if the account called is non-existent, as part of the design if the account called is non-existent, as part of the design
of the EVM. Account existence must be checked prior to calling if needed. of the EVM. Account existence must be checked prior to calling if needed.
Exceptions can be caught with the ``try``/``catch`` statement. Exceptions in external calls can be caught with the ``try``/``catch`` statement.
Exceptions can contain data that is passed back to the caller. Exceptions can contain data that is passed back to the caller.
This data consists of a 4-byte selector and subsequent :ref:`ABI-encoded<abi>` data. This data consists of a 4-byte selector and subsequent :ref:`ABI-encoded<abi>` data.
@ -611,9 +611,20 @@ that cannot be detected until execution time.
This includes conditions on inputs This includes conditions on inputs
or return values from calls to external contracts. or return values from calls to external contracts.
A ``Error(string)`` exception is generated in the following situations: A ``Error(string)`` exception (or an exception without data) is generated
in the following situations:
#. Calling ``require`` with an argument that evaluates to ``false``. #. Calling ``require`` with an argument that evaluates to ``false``.
#. If you perform an external function call targeting a contract that contains no code.
#. If your contract receives Ether via a public function without
``payable`` modifier (including the constructor and the fallback function).
#. If your contract receives Ether via a public getter function.
For the following cases, the error data from the external call
(if provided) is forwarded. This mean that it can either cause
an `Error` or a `Panic` (or whatever else was given):
#. If a ``.transfer()`` fails.
#. If you call a function via a message call but it does not finish #. If you call a function via a message call but it does not finish
properly (i.e., it runs out of gas, has no matching function, or properly (i.e., it runs out of gas, has no matching function, or
throws an exception itself), except when a low level operation throws an exception itself), except when a low level operation
@ -622,11 +633,6 @@ A ``Error(string)`` exception is generated in the following situations:
indicate failures by returning ``false``. indicate failures by returning ``false``.
#. If you create a contract using the ``new`` keyword but the contract #. If you create a contract using the ``new`` keyword but the contract
creation :ref:`does not finish properly<creating-contracts>`. creation :ref:`does not finish properly<creating-contracts>`.
#. If you perform an external function call targeting a contract that contains no code.
#. If your contract receives Ether via a public function without
``payable`` modifier (including the constructor and the fallback function).
#. If your contract receives Ether via a public getter function.
#. If a ``.transfer()`` fails.
You can optionally provide a message string for ``require``, but not for ``assert``. You can optionally provide a message string for ``require``, but not for ``assert``.