FGMPKey

FGMPKey

Identity of one listener registration, and the carrier of its ordering.

Declared in Plugins/GMP/Source/GMP/GMP/GMPKey.h:52

USTRUCT()
struct FGMPKey
{
    GENERATED_BODY()
public:
    FGMPKey(int64 In = 0) : Key(In) {}

    UPROPERTY()
    int64 Key;

    FORCEINLINE auto GetKey() const { return Key; }
    FORCEINLINE bool IsValid() const { return !!Key; }
    operator int64() const { return Key; }
    explicit operator bool() const { return IsValid(); }

    GMP_API static FGMPKey NextGMPKey();
    GMP_API static FGMPKey NextGMPKey(GMP::FGMPListenOptions Options);
};

What it is for

Every ListenMessage returns one. Two uses:

• Unregister a single listener — UnListenMessage(FMSGKEYFind(...), Key). Without the key you can only unregister all of an owner's listeners.
• Ordering — the Order from FGMPListenOptions is encoded into the high bits by NextGMPKey(Options).

Why order lives in the key

Sorting listeners by FGMPKey sorts them by Order first and by creation sequence second, because the low bits are a monotonically increasing counter. That gives two properties for free:

• lower Order runs first
• equal Order keeps registration order, since the counter breaks the tie

No separate ordering structure is maintained, and the pre-fire sort is a plain integer sort.

Validity

0 is the invalid key; IsValid() and explicit operator bool() both test that. A failed registration returns an invalid key rather than throwing, so a caller that cares must check.

The implicit operator int64() makes the value easy to log and compare, but also means an unchecked key converts silently to 0 in arithmetic contexts — prefer IsValid() to !Key in code others will read.

See also

ListenMessage family · FSigHandle · FGMPExtra