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[docs] Simplify some language for Error/cantFail in the programmer's manual.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301773 91177308-0d34-0410-b5e6-96231b3b80d8
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Lang Hames 2017-04-30 17:24:52 +00:00
parent 0a4ec8f0b2
commit 8456354f64
1 changed files with 9 additions and 10 deletions
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19
docs/ProgrammersManual.rst
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@ -776,22 +776,21 @@ readability.
Using cantFail to simplify safe callsites
"""""""""""""""""""""""""""""""""""""""""
Some functions may only fail for a subset of their inputs. For such functions
call-sites using known-safe inputs can assume that the result will be a success
value.
Some functions may only fail for a subset of their inputs, so calls using known
safe inputs can be assumed to succeed.
The cantFail functions encapsulate this by wrapping an assertion that their
argument is a success value and, in the case of Expected<T>, unwrapping the
T value from the Expected<T> argument:
T value:
.. code-block:: c++
Error mayFail(int X);
Expected<int> mayFail2(int X);
Error onlyFailsForSomeXValues(int X);
Expected<int> onlyFailsForSomeXValues2(int X);
void foo() {
cantFail(mayFail(KnownSafeValue));
int Y = cantFail(mayFail2(KnownSafeValue));
cantFail(onlyFailsForSomeXValues(KnownSafeValue));
int Y = cantFail(onlyFailsForSomeXValues2(KnownSafeValue));
...
}
@ -801,8 +800,8 @@ terminate the program on an error input, cantFile simply asserts that the result
is success. In debug builds this will result in an assertion failure if an error
is encountered. In release builds the behavior of cantFail for failure values is
undefined. As such, care must be taken in the use of cantFail: clients must be
certain that a cantFail wrapped call really can not fail under any
circumstances.
certain that a cantFail wrapped call really can not fail with the given
arguments.
Use of the cantFail functions should be rare in library code, but they are
likely to be of more use in tool and unit-test code where inputs and/or