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digitalmars.D.bugs - [Issue 2305] New: ".sort" on array of struct can use templated "opCmp"

reply d-bugmail puremagic.com writes:
http://d.puremagic.com/issues/show_bug.cgi?id=2305

           Summary: ".sort" on array of struct can use templated "opCmp"
           Product: D
           Version: unspecified
          Platform: PC
               URL: http://codepad.org/63qU9Ndr
        OS/Version: Windows
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: tsalm free.fr


Actually, to sort an array of "struct", ".sort" don't use a templated opCmp
method.

Here is an example that illustrate the problem (same as in the url) :

import tango.io.Stdout;

struct A{
 int i;
 static A opCall(int j){ A a; a.i=j; return a; }
 int opCmp(T)(T b) { static if (is(T:A)||is(T:A*)) return (i-b.i); else return
false;}
}

struct B{ // opposite ordering
 int i;
 static B opCall(int j){ B res; res.i=j; return res; }
 int opCmp(T)(T b) { static if (is(T:B)||is(T:B*)) return -(i-b.i); else return
false; }
}

void main()
{
 int a=1,b=2;

 A a2=A(a),b2=A(b);
 Stdout("A")(a2.opCmp(b2))(" ")(a2<b2).newline;
 auto aa2=[a2,b2];

 B a3=B(a),b3=B(b);
 Stdout("B")(a3.opCmp(b3))(" ")(a3<b3).newline;
 auto aa3=[a3,b3];

 aa2.sort;
 aa3.sort;

 foreach(v;aa2) Stdout( v.i )(" ");
 Stdout.newline;
 foreach(v;aa3) Stdout( v.i )(" ");
 Stdout.newline;
}


-- 
Aug 22 2008
parent "Jarrett Billingsley" <kb3ctd2 yahoo.com> writes:
<d-bugmail puremagic.com> wrote in message 
news:bug-2305-3 http.d.puremagic.com/issues/...
 http://d.puremagic.com/issues/show_bug.cgi?id=2305

           Summary: ".sort" on array of struct can use templated "opCmp"
           Product: D
           Version: unspecified
          Platform: PC
               URL: http://codepad.org/63qU9Ndr
        OS/Version: Windows
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: tsalm free.fr


 Actually, to sort an array of "struct", ".sort" don't use a templated 
 opCmp
 method.

 Here is an example that illustrate the problem (same as in the url) :

 import tango.io.Stdout;

 struct A{
 int i;
 static A opCall(int j){ A a; a.i=j; return a; }
 int opCmp(T)(T b) { static if (is(T:A)||is(T:A*)) return (i-b.i); else 
 return
 false;}
 }

 struct B{ // opposite ordering
 int i;
 static B opCall(int j){ B res; res.i=j; return res; }
 int opCmp(T)(T b) { static if (is(T:B)||is(T:B*)) return -(i-b.i); else 
 return
 false; }
 }

 void main()
 {
 int a=1,b=2;

 A a2=A(a),b2=A(b);
 Stdout("A")(a2.opCmp(b2))(" ")(a2<b2).newline;
 auto aa2=[a2,b2];

 B a3=B(a),b3=B(b);
 Stdout("B")(a3.opCmp(b3))(" ")(a3<b3).newline;
 auto aa3=[a3,b3];

 aa2.sort;
 aa3.sort;

 foreach(v;aa2) Stdout( v.i )(" ");
 Stdout.newline;
 foreach(v;aa3) Stdout( v.i )(" ");
 Stdout.newline;
 }


 -- 

Unsurprising. Templated functions/methods are not functions/methods until they are actually instantiated. As far as D is concerned, you have not overloaded opCmp. Also, you don't return "false" from opCmp. If something can't be compared, you should give an error (in this case, you can use static assert to give a compile-time error).
Aug 22 2008