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digitalmars.D.bugs - [Issue 408] New: Template instance matching doesn't work sometimes

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=408

           Summary: Template instance matching doesn't work sometimes
           Product: D
           Version: 0.169
          Platform: PC
        OS/Version: Windows
            Status: NEW
          Keywords: rejects-valid
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: burton-radons smocky.com


Code fails compilation with:

        argh.d(5): function math.matrix.f!(2u).f (S ) does not match argument
types (S )
        argh.d(5): cannot implicitly convert expression (*this) of type S to S

As far as I can tell it is valid code.

==
        struct S (uint C)
        {
                void argh ()
                {
                        f! (C) (*this);
                }
        }

        template f (uint C)
        {
                void f (S! (C) a)
                {
                }
        }

        alias S! (2) s;


--
Oct 08 2006
next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=408


burton-radons smocky.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |burton-radons smocky.com





Found it. If a template instantiation literal value is given the type "uint", D
casts it to "int" implicitly so it no longer works against a second
instantiation. So this works:

        struct O (int T)
        {
                .O! (T) f () { return *this; }
        }

        alias O! (2) o;

But this fails:

        struct O (uint T)
        {
                .O! (T) f () { return *this; }
        }

        alias O! (2) o;


--
Oct 08 2006
prev sibling next sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=408


bugzilla digitalmars.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID





This is working as designed (although the error message isn't great). The issue
is, is the template instance made from the argument before the cast to the
template value type, or after? D's design is to do make it from the original
type. In the third example, 2 is an int, but T is a uint, hence the two
instances are not the same.

The reason for this is so that template specializations can be added without
upsetting the name mangling.


--
Oct 16 2006
prev sibling parent d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=408






It's not complaining about the outside template instantiation, it's complaining
about the nested one. In other words, 2 is treated happily as a uint by an
explicit instantiation, but is not treated as anything compatible to a uint by
a dependent instantiation.

This rule (which doesn't exist in the documentation) isn't even applied
consistently! This, which has EXACTLY the same issue as the first example,
works quite happily:

        struct S (float C)
        {
                void argh ()
                {
                        f! (C) (*this);
                }
        }

        template f (float C)
        {
                void f (S! (C) a)
                {
                }
        }

        alias S! (2) s;

Try to make a design of this and you'll come out with spagghetti, there's no
rhyme or reason to it.


--
Oct 16 2006