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digitalmars.D.learn - Why can't I have overloading and generics?

reply Caligo <iteronvexor gmail.com> writes:
    struct B { }
    struct C { }
    struct D { }

    struct A {

      ref A foo(B item) {
        /* do something special. */
        return this;
      }

      ref A foo(T)(T item) if(is(T == C) || is(T == D)) {
        /* nothing special, do the same for C and D. */
        return this;
      }
    }

Is this unreasonable?  iirc, C++ supports this, but not D.  What's the
reason? Bug?

What's a good solution to this?

1. a generic `foo()` that uses `static if`s?

2. overload `foo()`, even if it means having function bodies that are
exactly same (code duplication).?

3. mixin templates?  I don't know about this because TDPL says it's
experimental, and I've tried and I get weird errors.
Mar 09 2012
next sibling parent reply sclytrack <sclytrack hotmail.com> writes:
On 03/10/2012 04:32 AM, Caligo wrote:

      struct B { }
      struct C { }
      struct D { }

      struct A {

        ref A foo(B item) {
          /* do something special. */
          return this;
        }

        ref A foo(T)(T item) if(is(T == C) || is(T == D)) {
          /* nothing special, do the same for C and D. */
          return this;
        }
      }

 Is this unreasonable?  iirc, C++ supports this, but not D.  What's the
 reason? Bug?

 What's a good solution to this?

 1. a generic `foo()` that uses `static if`s?

 2. overload `foo()`, even if it means having function bodies that are
 exactly same (code duplication).?

 3. mixin templates?  I don't know about this because TDPL says it's
 experimental, and I've tried and I get weird errors.



I don't know what the best solution is. But the following works.



import std.stdio;


     struct B { }
     struct C { }
     struct D { }

     struct A {

       ref A foo(T)(T item) if (is(T==B)) {
         /* do something special. */
				writeln("B");
         return this;
       }

       ref A foo(T)(T item) if(is(T == C) || is(T == D)) {
         /* nothing special, do the same for C and D. */
				writeln("C or D");
         return this;
       }
     }


int main()
{
	A a;
	B b;
	C c;
	a.foo(b);
	a.foo(c);
	writeln("Test");
	return 0;
}

-----------------------output

B
C or D
Test
Mar 10 2012
parent David <d dav1d.de> writes:
You can strip


 ref A foo(T)(T item) if (is(T==B)) {


down to:

ref A foo(T : B)(T item) // or to match your example
ref A foo(T == B)(T item)
Mar 10 2012
prev sibling next sibling parent "so" <so so.so> writes:
On Saturday, 10 March 2012 at 03:32:44 UTC, Caligo wrote:

     struct B { }
     struct C { }
     struct D { }

     struct A {

       ref A foo(B item) {
         /* do something special. */
         return this;
       }

       ref A foo(T)(T item) if(is(T == C) || is(T == D)) {
         /* nothing special, do the same for C and D. */
         return this;
       }
     }

 Is this unreasonable?  iirc, C++ supports this, but not D.  
 What's the
 reason? Bug?

 What's a good solution to this?

 1. a generic `foo()` that uses `static if`s?

 2. overload `foo()`, even if it means having function bodies 
 that are
 exactly same (code duplication).?

 3. mixin templates?  I don't know about this because TDPL says 
 it's
 experimental, and I've tried and I get weird errors.


When it comes to templates if it works in C++ and not in D, you 
can be sure it is a bug OR future!

For this one i am sure it is a bug. Rule is, when language 
resolves the function it first looks for exact matches then 
template overloads and i can't see anything wrong in your code. I 
am not sure but it is probably about "is". Its usage looks pretty 
in your code, it should not! :)
Mar 10 2012
prev sibling parent "Jesse Phillips" <jessekphillips+D gmail.com> writes:
Templates not overriding non-template functions is a bug

http://d.puremagic.com/issues/show_bug.cgi?id=1528
Mar 10 2012