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digitalmars.D - What is the syntax to test for specific types in templates

reply Derek Parnell <derek psych.ward> writes:
I want to ensure that the template can only be generated for certain data
types: integers and floating-point numbers only. I've seen something like
this done before but I cannot work it out fro the official documentation.

I think it should be something like ...

template foo(T)
{
   T foo(T x)
   {
      static if ( is(ulong T) ||
                  is(long T)  ||
                  is(uint T)  ||
                  is(int T)  ||
                  is(ushort T)  ||
                  is(short T)  ||
                  is(ubyte T)  ||
                  is(byte T) )
      {
         // ... code for integers ... //
      }
      else
      static if ( is(real T) ||
                  is(double T)  ||
                  is(float T) )
      {
         // ... code for floating points ... //
      }
      else
      {
         pragma(msg, "Only integers and floating points");
         static assert(0);
      }

   }
}

I know I can use template specialization but that is *way* too cumbersome
as I'd need three copies of the floating point template and eight copies of
the integer template. And seeing that templates were invented to avoid all
this copying it seems odd that there is not easy way to do multiple
specialization. 

Even if we could do ...

  template foo(T : (ulong, long, uint, int, ushort, short, ubyte, byte) )
  {
    // code for integers 
  }

  template foo(T : (real, double, float) )
  {
    // code for floating points
  }

would be useful but I don't think anything like this is allowed.

-- 
Derek
(skype: derek.j.parnell)
Melbourne, Australia
"Down with mediocracy!"
12/04/2006 2:07:10 PM
Apr 11 2006
parent reply Oskar Linde <Oskar_member pathlink.com> writes:
In article <138zdzputeyti$.16ay0g5ad0xj6$.dlg 40tude.net>, Derek Parnell says...
I want to ensure that the template can only be generated for certain data
types:...
I think it should be something like ...

template foo(T)
{
   T foo(T x)
   {
      static if ( is(ulong T) || ...

static if (is(T == ulong)) or maybe better for your application: is (T : int) for all T implicitly convertible to int. /Oskar
Apr 11 2006
parent Derek Parnell <derek psych.ward> writes:
On Wed, 12 Apr 2006 06:01:52 +0000 (UTC), Oskar Linde wrote:

 In article <138zdzputeyti$.16ay0g5ad0xj6$.dlg 40tude.net>, Derek Parnell
says...
I want to ensure that the template can only be generated for certain data
types:...
I think it should be something like ...

template foo(T)
{
   T foo(T x)
   {
      static if ( is(ulong T) || ...

static if (is(T == ulong)) or maybe better for your application: is (T : int) for all T implicitly convertible to int. /Oskar

Thanks, that works fine. In the docs is says "is ( Type == TypeSpecialization )" is one of the forms, but I had a mental block as I didn't recognise that 'Type' meant the template's 'type' parameter. A simple example of this form would be helpful ... template foo(T) { T foo(T bar) { static if ( is(T == real) || is(T == double) || is(T == float) ) { // Code for floating point types } else static if ( is(T == ulong) || is(T == long) || is(T == uint) || is(T == int) || is(T == ushort)|| is(T == short) || is(T == ubyte) || is(T == byte) ) { // Code for integer types } else { pragma(msg, "ERROR! foo!() Can only use an integer or floating point type"); static assert(0); } } } -- Derek (skype: derek.j.parnell) Melbourne, Australia "Down with mediocracy!" 12/04/2006 6:04:38 PM
Apr 12 2006