0a20c29367
This macro allows to write `mozilla::Result`-based code
similar to the rust try macro by using
gcc Statement Expressions [0],
which is a non-standard extension to gcc and clang.
This macro is used as an rvalue, while still returning early for error cases:
```
// Result<SuccessValue, E> Func();
Result<T, E> Bar() {
SuccessValue val = MOZ_TRY(Func());
// ...
}
```
This macro can only be used if `SuccessValue` is movable.
[0]: https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
Differential Revision: https://phabricator.services.mozilla.com/D235415
47 lines
1.8 KiB
C
47 lines
1.8 KiB
C
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
|
|
* vim: set ts=8 sts=2 et sw=2 tw=80:
|
|
* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
#ifndef mozilla_Try_h
|
|
#define mozilla_Try_h
|
|
|
|
#include "mozilla/Result.h"
|
|
|
|
/**
|
|
* MOZ_TRY(expr) is the C++ equivalent of Rust's `target = try!(expr);`, using
|
|
* gcc's statement expressions [0]. First, it evaluates expr, which must produce
|
|
* a Result value. On success, the result's success value is 'returned' as
|
|
* rvalue. On error, immediately returns the error result. This pattern allows
|
|
* to directly assign the success value:
|
|
*
|
|
* ```
|
|
* SuccessValue val = MOZ_TRY(Func());
|
|
* ```
|
|
*
|
|
* Where `Func()` returns a `Result<SuccessValue, E>` and is called in a
|
|
* function that returns `Result<T, E>`.
|
|
*
|
|
* [0]: https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
|
|
*/
|
|
#define MOZ_TRY(expr) \
|
|
__extension__({ \
|
|
auto mozTryVarTempResult = ::mozilla::ToResult(expr); \
|
|
if (MOZ_UNLIKELY(mozTryVarTempResult.isErr())) { \
|
|
return mozTryVarTempResult.propagateErr(); \
|
|
} \
|
|
mozTryVarTempResult.unwrap(); \
|
|
})
|
|
/**
|
|
* MOZ_TRY_VAR(target, expr) is the C++ equivalent of Rust's `target =
|
|
* try!(expr);`. First, it evaluates expr, which must produce a Result value. On
|
|
* success, the result's success value is assigned to target. On error,
|
|
* immediately returns the error result. |target| must be an lvalue.
|
|
*
|
|
* This macro is obsolete and its usages should be replaced with `MOZ_TRY`.
|
|
*/
|
|
#define MOZ_TRY_VAR(target, expr) (target) = MOZ_TRY(expr);
|
|
|
|
#endif // mozilla_Try_h
|