[Issue 1661] Not possible to specialize on template with integer parameter

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=1661





------- Comment #8 from onlystupidspamhere at yahoo.se  2008-02-29 14:07 -------
(In reply to comment #7)
> Am I right in thinking this is the actual syntax that should work?:
> 
> struct test_specialize(T : Number!(N), int N)
> {
>     void talk() { writefln("Ooh special - NUMBER N\n"); }
> }
> test_specialize!(Number!(5)) x;

I would expect it to be. But this issue isn't limited to int parameters. Other
primitive types don't work either. Also, more complex pattern matching fails:

  struct a(S, T) {}
  struct b(T : a!(N, a!(N, int)), N) {}
  alias a!(float,int) A;
  alias a!(float, A) B;
  b!(B, float) x; // fails, and so does b!(B) x;

foo.d:5: template instance b!(a!(float,a!(float,int) ) ,float) does not match
any template declaration
foo.d:5: Error: b!(a!(float,a!(float,int) ) ,float) is used as a type
foo.d:5: variable foo.x voids have no value

This is a bit problematic for someone creating a new compiler for D since it's
not really clear how complex types the language should be able to match. The
specification only mentions (http://www.digitalmars.com/d/1.0/template.html)
that they should be types. But that's a bit confusing since Number!(N) isn't a
valid type. You can't e.g. alias it, there's no parametrized alias syntax:

  alias IntNPair N = tuple!(int, N);

One could instantiate the code above with Number(float) or Number!(float), and
get tuple!(int, float).


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