[Issue 3917] New: opEquals for Ojbect could be more efficient

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=3917

           Summary: opEquals for Ojbect could be more efficient
           Product: D
           Version: 2.041
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: druntime
        AssignedTo: sean at invisibleduck.org
        ReportedBy: schveiguy at yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy at yahoo.com> 2010-03-09 12:42:34 PST ---
The implementation of opEquals in object_.d has an unnecessary recursive call. 
The complete implementation is this:

bool opEquals(Object lhs, Object rhs)
{
    // If aliased to the same object or both null => equal
    if (lhs is rhs) return true;

    // If either is null => non-equal
    if (lhs is null || rhs is null) return false;

    // If same exact type => one call to method opEquals
    if (typeid(lhs) == typeid(rhs)) return lhs.opEquals(rhs);

    // General case => symmetric calls to method opEquals
    return lhs.opEquals(rhs) && rhs.opEquals(lhs);
}

bool opEquals(TypeInfo lhs, TypeInfo rhs)
{
    // If aliased to the same object or both null => equal
    if (lhs is rhs) return true;

    // If either is null => non-equal
    if (lhs is null || rhs is null) return false;

    // If same exact type => one call to method opEquals
    if (typeid(lhs) == typeid(rhs)) return lhs.opEquals(rhs);

    // Factor out top level const
    // (This still isn't right, should follow same rules as compiler does for
type equality.)
    TypeInfo_Const c = cast(TypeInfo_Const) lhs;
    if (c)
        lhs = c.base;
    c = cast(TypeInfo_Const) rhs;
    if (c)
        rhs = c.base;

    // General case => symmetric calls to method opEquals
    return lhs.opEquals(rhs) && rhs.opEquals(lhs);
}


The third if statement that compares two typeids recurses into opEquals for
typeinfos.  In the typeinfo comparison, the typeinfos should never be null, and
the typeinfos of the typeinfo will always be identical (TypeInfo_Class).  In
addition, the stuff at the end dealing with const will never come into play
because the dynamic typeinfo (the classinfo) never deals with const.

I'd propose to rewrite the opEquals as follows:

bool opEquals(Object lhs, Object rhs)
{
    // If aliased to the same object or both null => equal
    if (lhs is rhs) return true;

    // If either is null => non-equal
    if (lhs is null || rhs is null) return false;

    // If same exact type => one call to method opEquals
    if (typeid(lhs) is typeid(rhs) || typeid(lhs).opEquals(typeid(rhs))) return
lhs.opEquals(rhs);

    // General case => symmetric calls to method opEquals
    return lhs.opEquals(rhs) && rhs.opEquals(lhs);
}

I don't know what else the opEquals that compares typeinfos is for, because
it's not a public function, so it could potentially be removed.

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