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[Docs] Clarify boolean conversion for Error and Expected<T> in the Programmer's

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Manual.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@264135 91177308-0d34-0410-b5e6-96231b3b80d8
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Lang Hames 2016-03-23 03:18:16 +00:00
parent ab71fdec0a
commit 3821992393
1 changed files with 16 additions and 4 deletions
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docs/ProgrammersManual.rst
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@ -356,12 +356,24 @@ that inherits from the ErrorInfo utility:
return Error::success();
}
Error values can be implicitly converted to bool: true for error, false for
success, enabling the following idiom:
.. code-block::
if (auto Err = mayFail())
return Err;
// Success! We can proceed.
For functions that can fail but need to return a value the ``Expected<T>``
utility can be used. Values of this type can be constructed with either a
``T``, or a ``Error``. Values are implicitly convertible to boolean: true
for success, false for error. If success, the ``T`` value can be accessed via
the dereference operator. If failure, the ``Error`` value can be extracted
using the ``takeError()`` method:
``T``, or a ``Error``. Expected<T> values are also implicitly convertible to
boolean, but with the opposite convention to Error: true for success, false for
error. If success, the ``T`` value can be accessed via the dereference operator.
If failure, the ``Error`` value can be extracted using the ``takeError()``
method. Idiomatic usage looks like:
.. code-block:: c++