[SOLVED] Define field with macro, but Field cannot have type 'void' and/or Expected ')'

Define field with macro, but Field cannot have type 'void' and/or Expected ')'

Trying to simplify writing boiler plate, but I get Field cannot have type 'void' and / or Expected ')'

Newbie c++, I've seen a bunch questions like this, but still can't figure it out. The errors are still too cryptic to me to able to google them..

#define GAME_STAT(Stat) \
    UPROPERTY(BlueprintReadOnly, Category = "Stats", ReplicatedUsing = OnRep_##Stat##) \
    FGameplayAttributeData ##Stat##; \
    GAME_STAT_ACCESS(UGameStats, ##Stat##); \
    UFUNCTION() \
    virtual void OnRep_##Stat##(const FGameplayAttributeData& Old##Stat##);
    
GAME_STAT("Health")

I want to generate the code with word "Health" instead of stand-in "Stat"

Thanks!

Solution

## is for pasting tokens together, but it looks like you think it is "reverse stringification".
It's also a binary operator, not an "around-ary" operator.

That is,

#define hello(x) Hello_##x
hello(World)

will produce

Hello_World

This should work (but is thoroughly untested):

#define GAME_STAT(Stat) \
    UPROPERTY(BlueprintReadOnly, Category = "Stats", ReplicatedUsing = OnRep_##Stat) \
    FGameplayAttributeData Stat; \
    GAME_STAT_ACCESS(UGameStats, Stat); \
    UFUNCTION() \
    virtual void OnRep_##Stat(const FGameplayAttributeData& Old##Stat);
    
GAME_STAT(Health)