GMPArchive

GMPArchive

The archive types GMP serialises through.

Declared in Plugins/GMP/Source/GMP/GMP/GMPArchive.h

class FGMPMemoryArchive : public FMemoryArchive
{
protected:
    virtual FArchive& operator<<(UObject*& Object) override;
};

class GMP_API FGMPMemoryWriter : public FGMPMemoryArchive { ... };
class GMP_API FGMPMemoryReader : public FGMPMemoryArchive { ... };
class GMP_API FGMPNetBitWriter : public FNetBitWriter     { ... };
class GMP_API FGMPNetBitReader : public FNetBitReader     { ... };

Two pairs

Pair	For	Object references
FGMPMemoryWriter / FGMPMemoryReader	plain memory, sized buffer	via the overridden operator<<
FGMPNetBitWriter / FGMPNetBitReader	the network path	UPackageMap-aware, so references resolve on the far side

The part that matters

FGMPMemoryArchive exists to override one thing:

virtual FArchive& operator<<(UObject*& Object) override;

A default memory archive would serialise the raw pointer value, which is meaningless once it leaves the process. Overriding it is what makes object references survive — and it is the reason to use these types rather than a plain FMemoryWriter.

FGMPMemoryWriter writes its size through a caller-supplied uint32*, so the buffer length travels with the payload.

Adjacent, but separate

GMP also bridges JSON, Protobuf (upb) and YAML to UStruct reflection, with FGMPValueOneOf for dynamic access to a decoded value that has no static type. These are independent of the messaging core and usable on their own; they are enabled by their own build switches (GMP_WITH_UPB, GMP_WITH_YAML, GMP_WITH_JSONDOM).

See also

FGMPStructUnion · FRpcMessageUtils · Build switches