How to modify integer inside of a lambda function?

[Krileon]

Still working on my C++ and having a bit of a hard time with this one. Basically I’m looping through an array of FHitResult using RemoveAll and removing hits that are not visible using a line trace, but I want to stop doing that once I reach a predefined limit. Below is what I have so far, but doesn’t work.

UWorld* World = WorldContextObject->GetWorld();
int Found = 0;

Hits.RemoveAll([ World, TraceChannel, Location, Found, Limit ]( const FHitResult& Hit ) mutable {
	FHitResult TraceHitResult;

	if ( Found >= Limit ) {
		return false;
	}

	if ( World->LineTraceSingleByChannel( TraceHitResult, ( ! Location.IsZero() ? Location : Hit.TraceStart ), Hit.ImpactPoint, TraceChannel ) ) {
		return true;
	}

	Found++;

	return false;
});

This throws the below error.

\Engine\Source\Runtime\Core\Public\Containers\Array.h(2595): error C2672: 'Invoke': no matching overloaded function found
\Engine\Source\Runtime\Core\Public\Templates\Invoke.h(63): note: could be 'unknown-type Invoke(PtrMemFunType,TargetType &&,ArgTypes &&...)'
\Engine\Source\Runtime\Core\Public\Containers\Array.h(2595): note: 'unknown-type Invoke(PtrMemFunType,TargetType &&,ArgTypes &&...)': could not deduce template argument for 'ObjType'
\Engine\Source\Runtime\Core\Public\Templates\Invoke.h(51): note: or       'unknown-type Invoke(ReturnType ObjType::* ,TargetType &&)'
\Engine\Source\Runtime\Core\Public\Containers\Array.h(2595): note: 'unknown-type Invoke(ReturnType ObjType::* ,TargetType &&)': could not deduce template argument for 'ReturnType ObjType::* ' from 'const PREDICATE_CLASS'
        with
        [
            PREDICATE_CLASS=UTraceAttackHelpers::GetLimitedVisibleAttacksByRef::<lambda_1>
        ]

Can’t quite wrap my head around what it means. Anyone have any suggestions? To give some context lets say the Limit is 10. I want it to stop once doing traces it reaches 10 successful visible hits.

[matrem84]

Perhaps you should add the return type to your lambda in this case.

[Lardo_Deepdelver]

Seems there is no overload for a mutable lambda,
capturing Found by reference instead should do the trick.

Hits.RemoveAll([ World, TraceChannel, Location, &Found, Limit ]( const FHitResult& Hit ) {
	FHitResult TraceHitResult;

	if ( Found >= Limit ) {
		return false;
	}

	if ( World->LineTraceSingleByChannel( TraceHitResult, ( ! Location.IsZero() ? Location : Hit.TraceStart ), Hit.ImpactPoint, TraceChannel ) ) {
		return true;
	}

	Found++;

	return false;
});

[Krileon]

That worked. Needed to remove mutable entirely and just pass by reference. Thanks!