From a0f517fc1596b25bba11cfd6a73f54aabec4546c Mon Sep 17 00:00:00 2001 From: Lang Hames Date: Wed, 23 Mar 2016 03:18:16 +0000 Subject: [Docs] Clarify boolean conversion for Error and Expected in the Programmer's Manual. llvm-svn: 264135 --- llvm/docs/ProgrammersManual.rst | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) (limited to 'llvm/docs/ProgrammersManual.rst') diff --git a/llvm/docs/ProgrammersManual.rst b/llvm/docs/ProgrammersManual.rst index 1258ad6..5ad5113 100644 --- a/llvm/docs/ProgrammersManual.rst +++ b/llvm/docs/ProgrammersManual.rst @@ -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`` 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 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++ -- cgit v1.1