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D - functions, delegates and templates

reply "Carlos Santander B." <carlos8294 msn.com> writes:
I have never used delegates in my life. Now I'm trying to start with D. I
think this should be legal:

template gen (T) {
    T max (T a,T b) {
        return (a>b?a:b);
    }

    bit comp(T a,T b,T delegate (T,T) f) {      /*************/
       return a==f(a,b);
    }
}

instance gen(int) intGen;
instance gen(real) realGen;
instance gen(char[]) strGen;

void main() {
    int a=45,b=32;
    real c=-12.3,d=2.4;
    char[] e='hola',f='chao';

    intGen.comp(a,b,intGen.max);
    realGen.comp(c,d,realGen.max);
    strGen.comp(e,f,strGen.max);
}

If I change delegate for function in the comp function, it doesn't work
either. Both ways, I get non-matching arguments. Is the code correct or am I
missing something?
The workaround that I've tried was to declare as a function, and also
declare 3 function pointers in main pointing to each max function, but I
think there must be another way to do it.


-------------------------
Carlos Santander


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Mar 05 2003
parent "Mike Wynn" <mike.wynn l8night.co.uk> writes:
a delegate is an object and the method to call (unlike a C++ pointer to
member func)

try this

template gen (T) {
    T max (T a,T b) {
        return (a>b?a:b);
    }
  class Maxer {
  T getmax( T a, T b ) { return max( a,b ); }
  }

  alias T (*compfunc)( T, T );

    bit comp(T a,T b,compfunc f) {      /*************/
       return a==f(a,b);
    }

  alias T delegate( T, T ) compdel;

    bit comp(T a,T b, compdel f) {      /*************/
       return a==f(a,b);
    }
}

instance gen(int) intGen;
instance gen(real) realGen;
instance gen(char[]) strGen;

int main( char[][] args ) {
    int a=45,b=32;
    real c=-12.3,d=2.4;
    char[] e='hola',f='chao';

    intGen.comp(a,b, &intGen.max);
    realGen.comp(c,d, &realGen.max);
    strGen.comp(e,f, &strGen.max);

    intGen.comp(a,b, &(new intGen.Maxer).getmax );
    realGen.comp(c,d,&(new realGen.Maxer).getmax );
    strGen.comp(e,f, &(new strGen.Maxer).getmax );

  return 0;
}

not unlike C/C++ you NEED the & to get a func ptr, or delegate

intGen.max  is int(int,int) not int(*)(int,int)


"Carlos Santander B." <carlos8294 msn.com> wrote in message
news:b45tmb$2c47$1 digitaldaemon.com...
 I have never used delegates in my life. Now I'm trying to start with D. I
 think this should be legal:

 template gen (T) {
     T max (T a,T b) {
         return (a>b?a:b);
     }

     bit comp(T a,T b,T delegate (T,T) f) {      /*************/
        return a==f(a,b);
     }
 }

 instance gen(int) intGen;
 instance gen(real) realGen;
 instance gen(char[]) strGen;

 void main() {
     int a=45,b=32;
     real c=-12.3,d=2.4;
     char[] e='hola',f='chao';

     intGen.comp(a,b,intGen.max);
     realGen.comp(c,d,realGen.max);
     strGen.comp(e,f,strGen.max);
 }

 If I change delegate for function in the comp function, it doesn't work
 either. Both ways, I get non-matching arguments. Is the code correct or am

 missing something?
 The workaround that I've tried was to declare as a function, and also
 declare 3 function pointers in main pointing to each max function, but I
 think there must be another way to do it.


 -------------------------
 Carlos Santander


 ---
 Outgoing mail is certified Virus Free.
 Checked by AVG anti-virus system (http://www.grisoft.com).
 Version: 6.0.459 / Virus Database: 258 - Release Date: 2003-02-25

Mar 05 2003