http://d.puremagic.com/issues/show_bug.cgi?id=2482

           Summary: Spec does not reference about special x functions in
                    TypeInfo_Struct
           Product: D
           Version: 2.019
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: spec
          Severity: normal
          Priority: P2
         Component: www.digitalmars.com
        AssignedTo: bugzilla@digitalmars.com
        ReportedBy: schveiguy@yahoo.com


The compiler treats certain operator overloads in structs in a special manner. Specifically, if an opCmp, opEquals, toHash or toString function matches a specific signature, a function pointer to that function is stored in the corresponding TypeInfo_Struct for that struct.

However, if the signatures are not correct, then the function pointer is not copied.  The result is that certain builtin functions or types (or user types which use the typeinfo to get at such functions) are not calling the user-defined functions accessed through the TypeInfo_Struct members.

Nowhere in the spec does it mention this, or have a list of what those signatures should be.  Also, some of the spec's examples use the wrong signature for examples of those functions.  For instance, the opCmp example for structs:

struct Pair
{
    int a, b;
    int opCmp(Pair rhs)
    {
        if (a!=rhs.a) return a-rhs.a;
        return b-rhs.b;
    }
}

This opCmp would *not* be used to sort an array of Pair types.

I think the spec should outline the four special functions mentioned above (opCmp, opEquals, toHash, toString), and what specific signature they should be for the compiler to recognize them.  Also, the above example should be updated to reflect the correct version:

struct Pair
{
    int a, b;
    int opCmp(const Pair *rhs) const
    {
        if (a!=rhs.a) return a-rhs.a;
        return b-rhs.b;
    }
}


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