On Scope Exit Macro

ON_SCOPE_EXIT takes a block of code that runs automatically when the current scope ends, no matter how it ends: reaching the closing brace, an early return, or a break/continue out of a loop.

This is really handy when a function has a lot of exit conditions, because you don’t have to duplicate the cleanup code before every return.

#include "Misc/ScopeExit.h"

void UMyComponent::PlayPreview(ULevelSequence* Sequence)
{
    ALevelSequenceActor* LevelSequenceActor = SpawnPreviewActor(Sequence);
    ULevelSequencePlayer* LevelSequencePlayer = LevelSequenceActor->GetSequencePlayer();

    ON_SCOPE_EXIT
    {
        // Runs on every return below
        LevelSequenceActor->Destroy();
    };

    if (!IsValid(LevelSequencePlayer))
    {
        return;
    }

    if (!LevelSequencePlayer->IsPlaying())
    {
        return;
    }

    // ...
}

Don’t forget the semicolon after the closing brace. The macro creates a variable initialized with a lambda, so }; is required or it won’t compile.

Variables are captured by reference. Declare ON_SCOPE_EXIT after the variables it uses, otherwise they won’t exist yet.

Only register the cleanup once the thing you want to clean up actually exists. In the example above the ON_SCOPE_EXIT comes after spawning the actor, so we never try to destroy a nullptr.