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604d5f5bca
For example, consider cases where we want to propagate errors only in
specific instances:
auto result = read_data(); // something like ErrorOr<ByteBuffer>
if (result.is_error() && result.error().code() != EINTR)
continue;
auto bytes = TRY(result);
The TRY invocation will currently copy the byte buffer when the
expression (in this case, just a local variable) is stored into
_temporary_result.
This patch binds the expression to a reference to prevent such copies.
In less trival invocations (such as TRY(some_function()), this will
incur only temporary lifetime extensions, i.e. no functional change.
45 lines
2.7 KiB
C
45 lines
2.7 KiB
C
/*
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* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Diagnostics.h>
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#include <AK/StdLibExtras.h>
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// NOTE: This macro works with any result type that has the expected APIs.
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// It's designed with AK::Result and AK::Error in mind.
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//
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// It depends on a non-standard C++ extension, specifically
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// on statement expressions [1]. This is known to be implemented
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// by at least clang and gcc.
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// [1] https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html
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//
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// If the static_assert below is triggered, it means you tried to return a reference
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// from a fallible expression. This will not do what you want; the statement expression
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// will create a copy regardless, so it is explicitly disallowed.
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#define TRY(expression) \
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({ \
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/* Ignore -Wshadow to allow nesting the macro. */ \
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AK_IGNORE_DIAGNOSTIC("-Wshadow", \
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auto&& _temporary_result = (expression)); \
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static_assert(!::AK::Detail::IsLvalueReference<decltype(_temporary_result.release_value())>, \
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"Do not return a reference from a fallible expression"); \
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if (_temporary_result.is_error()) [[unlikely]] \
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return _temporary_result.release_error(); \
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_temporary_result.release_value(); \
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})
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#define MUST(expression) \
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({ \
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/* Ignore -Wshadow to allow nesting the macro. */ \
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AK_IGNORE_DIAGNOSTIC("-Wshadow", \
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auto&& _temporary_result = (expression)); \
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static_assert(!::AK::Detail::IsLvalueReference<decltype(_temporary_result.release_value())>, \
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"Do not return a reference from a fallible expression"); \
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VERIFY(!_temporary_result.is_error()); \
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_temporary_result.release_value(); \
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})
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