• Peter Neubauer (34/34) Jun 29 2013 Please explain why this error happens in the following code:
• Michael (6/41) Jul 03 2013 I am not sure if this behavior is intended. Since "conv" is a

Peter Neubauer <peterneubauer2 gmail.com> writes:

Please explain why this error happens in the following code:

import std.algorithm;

struct S
{
   void foo ()
   {
     int f1 (int a) { return conv(a); }
     int delegate (int) f2 = &conv;

     int[] x = [1, 2, 3];
     x.map!conv;    // ERROR
     x.map!f1;      // fine
     x.map!f2;      // also fine
   }

   int conv (int a)
   {
     return a+1;
   }
}

--- compile output:

/usr/include/d/std/algorithm.d(404): Error: this for conv needs to be 
type S not type MapResult!(conv, int[])
/usr/include/d/std/algorithm.d(438): Error: this for conv needs to be 
type S not type MapResult!(conv, int[])
/usr/include/d/std/algorithm.d(450): Error: this for conv needs to be 
type S not type MapResult!(conv, int[])
/usr/include/d/std/algorithm.d(390): Error: template instance 
std.algorithm.MapResult!(conv, int[]) error instantiating
/home/peter/proggen/goliza.reduced/gtp.d(12):        instantiated from 
here: map!(int[])
/home/peter/proggen/goliza.reduced/gtp.d(12): Error: template instance 
std.algorithm.map!(conv).map!(int[]) error instantiating

---

Thanks,
-Peter

"Michael" <pongad gmail.com> writes:

On Saturday, 29 June 2013 at 19:44:00 UTC, Peter Neubauer wrote:
 Please explain why this error happens in the following code:

 import std.algorithm;

 struct S
 {
   void foo ()
   {
     int f1 (int a) { return conv(a); }
     int delegate (int) f2 = &conv;

     int[] x = [1, 2, 3];
     x.map!conv;    // ERROR
     x.map!f1;      // fine
     x.map!f2;      // also fine
   }

   int conv (int a)
   {
     return a+1;
   }
 }

 --- compile output:

 /usr/include/d/std/algorithm.d(404): Error: this for conv needs 
 to be type S not type MapResult!(conv, int[])
 /usr/include/d/std/algorithm.d(438): Error: this for conv needs 
 to be type S not type MapResult!(conv, int[])
 /usr/include/d/std/algorithm.d(450): Error: this for conv needs 
 to be type S not type MapResult!(conv, int[])
 /usr/include/d/std/algorithm.d(390): Error: template instance 
 std.algorithm.MapResult!(conv, int[]) error instantiating
 /home/peter/proggen/goliza.reduced/gtp.d(12):        
 instantiated from here: map!(int[])
 /home/peter/proggen/goliza.reduced/gtp.d(12): Error: template 
 instance std.algorithm.map!(conv).map!(int[]) error 
 instantiating

 ---

 Thanks,
 -Peter

I am not sure if this behavior is intended. Since "conv" is a 
instance method of S, it has an implicit "this" which must be of 
type S. I suspect that the map template tries to invoke conv in 
the context of MapResult. I hope template masters can give you a 
more complete explanation though.