[Issue 5281] Equality among arrays of Bigints

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=5281


Don <clugdbug at yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch, wrong-code
                 CC|                            |clugdbug at yahoo.com.au
         Depends on|                            |3659
           Severity|normal                      |critical


--- Comment #2 from Don <clugdbug at yahoo.com.au> 2010-12-01 23:56:02 PST ---
This is difficult. The patch (below) fixes the problem, and I believe it's
correct. The problem is, that applying it causes Phobos to break, because it
has
been relying on this bug. And I don't know how to modify Phobos to fix it.
Specifically, Tuple and Variant are affected.
There's a cluster of bugs related to the problem, eg: bug 3659 ("Too much
exegesis on opEquals", bug 3607 "Problems with struct opEquals and const").
But the major problem is that with a const ref signature, opEquals cannot
perform comparisons with rvalues. So the code below fails
----
struct Foo
{
    bool opEquals(ref const Foo f) const  { return true; }
}

Foo foo()
{
    Foo result;
    return result;
}

void main()
{
    Foo f;
//    assert(f == foo()); // does not compile
}
----------
To make this patch work with the existing Phobos, while bug 3659 is not fixed,
change
            if (!eq)
                fdx->error("type signature should be %s not %s"
into
            if (!eq && !td)
                fdx->error("type signature should be %s not %s"


PATCH:
StructDeclaration::semantic in struct.c
Around line 503,

        tfeqptr = new TypeFunction(parameters, Type::tbool, 0, LINKd);
        tfeqptr->mod = MODconst;
        tfeqptr = (TypeFunction *)tfeqptr->semantic(0, sc2);

        Dsymbol *s = search_function(this, Id::eq);
        FuncDeclaration *fdx = s ? s->isFuncDeclaration() : NULL;
+        TemplateDeclaration *td = s ? s->isTemplateDeclaration() : NULL;
+        if (td)
+        {
+            Expressions arguments;
+            arguments.setDim(1);
+            arguments.data[0] = (void*) param;
+            fdx = td->deduceFunctionTemplate(sc, loc, NULL, NULL, &arguments,
1);
+        }

        if (fdx)
        {
            eq = fdx->overloadExactMatch(tfeqptr);
            if (!eq)
                fdx->error("type signature should be %s not %s",
tfeqptr->toChars(), fdx->type->toChars());
        }
-        TemplateDeclaration *td = s ? s->isTemplateDeclaration() : NULL;
-        // BUG: should also check that td is a function template, not just a
template

-        if (!eq && !td)
+        if (!eq)
            eq = buildOpEquals(sc2);

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