Copyright (C) 1994, Digital Equipment Corporation           

| 

RTType provides access to the runtime type system. \index{runtime type} \index{type!runtime}

Each reference type is assigned a unique typecode. A typecode is ``proper'' if it lies in the range [0..MaxTypecode()]. The proper typecodes include all those that correspond to actual types in the running Modula-3 program. Other typecodes, proper and improper, may be used internally by the runtime system and garbage collector.

Although the language requires that typecodes exist only for object types and for traced reference types (including NULL), the implementation of RTType also provides typecodes for untraced reference types.

The values returned by the builtin operation TYPECODE correspond to (a subset of) the proper typecodes.

INTERFACE RTType;

IMPORT RT0;

TYPE Typecode = RT0.Typecode;

CONST NoSuchType: Typecode = LAST(Typecode);

A reserved typecode that represents unknown types.

PROCEDURE MaxTypecode(): Typecode;

Return the largest proper typecode.

PROCEDURE IsSubtype(a, b: Typecode): BOOLEAN;

Return TRUE iff the type corresponding to a is a subtype of the type corresponding to b. It is a checked runtime error if either a or b is not a proper typecode.

PROCEDURE Supertype(tc: Typecode): Typecode;

Return the typecode of the declared supertype of the object type corresponding to tc. If tc corresponds to ROOT, UNTRACED ROOT or a non-object reference type, return NoSuchType. It is a checked runtime error if tc is not a proper typecode.

PROCEDURE IsTraced(tc: Typecode): BOOLEAN;

Return TRUE iff the type corresponding to tc is traced.

PROCEDURE Get(tc: Typecode): RT0.TypeDefn;

Return a pointer to the typecell with typecode tc. It is a checked runtime error to pass an improper typecode.

PROCEDURE GetNDimensions(tc: Typecode): CARDINAL;

Return the number of open dimensions of the open array type that corresponds to tc's referent. If tc's referent is not an open array, return 0.

END RTType.