Understanding Macros of Macros?

Development Programming & Scripting C++
, , , ,
1

Hello there,

i am working with the GameplayAbilitySystem from Unreal and found this Code snippet in the AttributeSet.h File:

/**
 * This defines a set of helper functions for accessing and initializing attributes, to avoid having to manually write these functions.
 * It would creates the following functions, for attribute Health
 *
 *	static FGameplayAttribute UMyHealthSet::GetHealthAttribute();
 *	FORCEINLINE float UMyHealthSet::GetHealth() const;
 *	FORCEINLINE void UMyHealthSet::SetHealth(float NewVal);
 *	FORCEINLINE void UMyHealthSet::InitHealth(float NewVal);
 *
 * To use this in your game you can define something like this, and then add game-specific functions as necessary:
 * 
 *	#define ATTRIBUTE_ACCESSORS(ClassName, PropertyName) \
 *	GAMEPLAYATTRIBUTE_PROPERTY_GETTER(ClassName, PropertyName) \
 *	GAMEPLAYATTRIBUTE_VALUE_GETTER(PropertyName) \
 *	GAMEPLAYATTRIBUTE_VALUE_SETTER(PropertyName) \
 *	GAMEPLAYATTRIBUTE_VALUE_INITTER(PropertyName)
 * 
 *	ATTRIBUTE_ACCESSORS(UMyHealthSet, Health)
 */

On the otherhand i saw an example of this in the GASDocumentation from tranek (GASDocumentation/GDAttributeSetBase.h at master · tranek/GASDocumentation · GitHub)

// Uses macros from AttributeSet.h
#define ATTRIBUTE_ACCESSORS(ClassName, PropertyName) \
	GAMEPLAYATTRIBUTE_PROPERTY_GETTER(ClassName, PropertyName) \
	GAMEPLAYATTRIBUTE_VALUE_GETTER(PropertyName) \
	GAMEPLAYATTRIBUTE_VALUE_SETTER(PropertyName) \
	GAMEPLAYATTRIBUTE_VALUE_INITTER(PropertyName)

I dont really understand how this code works. A is understood macro is just an alias for a bunch of code or values. So is ATTRIBUTE_ACCESSORS actually an alias for the code behind GAMEPLAYATTRIBUTE_PROPERTY_GETTER, GAMEPLAYATTRIBUTE_VALUE_GETTER, and so on? A macro of macros if you want to call it that, right?

2

Wow… That looks pretty bad. Would have just written 1 function that returns a UObject for an ability and 1 function that returns an enum per attribute or something like that. Macros shouldn’t be used when not necessary. They are just text which will be copypasted all over the place.

1 Like