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96eeb6f4ff
This is good practice to avoid pessimisations. Left comments for the reasoning why ctors should be noexcept. There are some tricky cases where we intentionally want throwing move ctors/assignments. But those cases should really be reviewed, since some of those can be replaced with more idiomatic copy/move-and-swap.
51 lines
1.7 KiB
C++
51 lines
1.7 KiB
C++
#pragma once
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///@file
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#include <utility>
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#include <cassert>
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#include <exception>
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/**
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* A trivial class to run a function at the end of a scope.
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*/
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template<typename Fn>
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class [[nodiscard("Finally values must be used")]] Finally
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{
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private:
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Fn fun;
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bool movedFrom = false;
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public:
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Finally(Fn fun) : fun(std::move(fun)) { }
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// Copying Finallys is definitely not a good idea and will cause them to be
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// called twice.
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Finally(Finally &other) = delete;
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// NOTE: Move constructor can be nothrow if the callable type is itself nothrow
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// move-constructible.
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Finally(Finally && other) noexcept(std::is_nothrow_move_constructible_v<Fn>)
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: fun(std::move(other.fun))
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{
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other.movedFrom = true;
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}
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~Finally() noexcept(false)
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{
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try {
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if (!movedFrom)
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fun();
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} catch (...) {
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// finally may only throw an exception if exception handling is not already
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// in progress. if handling *is* in progress we have to return cleanly here
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// but are still prohibited from doing so since eating the exception would,
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// in almost all cases, mess up error handling even more. the only good way
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// to handle this is to abort entirely and leave a message, so we'll assert
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// (and rethrow anyway, just as a defense against possible NASSERT builds.)
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if (std::uncaught_exceptions()) {
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assert(false &&
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"Finally function threw an exception during exception handling. "
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"this is not what you want, please use some other methods (like "
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"std::promise or async) instead.");
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}
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throw;
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}
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}
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};
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