How do I sort an TArray of objects with private constructors?

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1

I have an array of ParticleSystemComponent pointers that I am trying to sort by name (in my test code the sorter always returns true).

// my sorting function
inline static bool WeaponMuzzleSort(const UParticleSystemComponent One, const UParticleSystemComponent Two)
{
	return true;
}

// my calling code
TArray<UParticleSystemComponent*>& MFArray;
MFArray.Sort(WeaponMuzzleSort);

When I attempt to compile this code I get the following error:

//...

    25>D:\Develop\Sandman\root\UE4\Engine\Source\Runtime\Core\Public\Templates\Sorting.h(51): error C2248: 'UParticleSystemComponent::UParticleSystemComponent' : cannot access private member declared in class 'UParticleSystemComponent'
    25>          D:\Develop\Sandman\root\UE4\Engine\Source\Runtime\Engine\Classes\Particles/ParticleSystemComponent.h(253) : see declaration of 'UParticleSystemComponent::UParticleSystemComponent'
    25>          D:\Develop\Sandman\root\UE4\Engine\Source\Runtime\Engine\Classes\Particles/ParticleSystemComponent.h(251) : see declaration of 'UParticleSystemComponent'
    25>          D:\Develop\Sandman\root\UE4\Engine\Source\Runtime\Core\Public\Templates\Sorting.h(50) : while compiling class template member function 'bool TDereferenceWrapper<T *,PREDICATE_CLASS>::operator ()(T *,T *) const'
    25>          with
    25>          [
    25>              T=UParticleSystemComponent
    25>  ,            PREDICATE_CLASS=bool (UParticleSystemComponent,UParticleSystemComponent)
    25>          ]
    25>          D:\Develop\Sandman\root\UE4\Engine\Source\Runtime\Core\Public\Templates\Sorting.h(90) : see reference to function template instantiation 'bool TDereferenceWrapper<T *,PREDICATE_CLASS>::operator ()(T *,T *) const' being compiled
    25>          with

//...

It appears that the issue is that UParticleSystemComponent has a private constructor (as defined in the macro GENERATED_UCLASS_BODY()) and the Sort function needs a public constructor in order to work.

This seems like a super routine problem (sorting an array of components) so I was wondering if there is any quick code solutions for this other than manually looping through the array and shuffling it around.

2

After digging around the engine code I found a solution:

I changed the parameters of WeaponMuzzleSort to non-const references and that fixes it.

inline static bool WeaponMuzzleSort(UParticleSystemComponent& One, UParticleSystemComponent& Two)
{
return true;
}
 
// my calling code
TArray<UParticleSystemComponent*>& MFArray;
MFArray.Sort(WeaponMuzzleSort);