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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
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.
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
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``.
#. 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
properly (i.e., it runs out of gas, has no matching function, or
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``.
#. If you create a contract using the ``new`` keyword but the contract
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``.