Delegates and classes for custom code.

[Simen Kjærås]

On Wednesday, 18 April 2018 at 01:12:33 UTC, Chris Katko wrote:
> My only questions are:
[snip]

How's about this one:

import std.stdio : writefln;

struct data_to_access_t
{
     int tacos;
}

class Abc(T, alias Fn) {
     T data;

     this(T data) {
         this.data = data;
     }

     void execute() {
         Fn(data);
     }
}

Abc!(T, Fn) abc(alias Fn, T)(T data) {
     return new Abc!(T, Fn)(data);
}

unittest {
     data_to_access_t  d;
     auto a = abc!((f) => writefln("test  %d", f.tacos))(d);
     a.execute();
}

One problem with this approach is that two seemingly identical 
instantiations are different types. This may or may not be a 
problem in your specific case. If it is:

import std.stdio : writefln;
import std.functional : toDelegate;

struct data_to_access_t
{
     int tacos;
}

class Abc(T) {
     T data;
     void delegate(T) Fn;

     this(T data, void delegate(T) Fn) {
         this.data = data;
         this.Fn = Fn;
     }

     void execute() {
         Fn(data);
     }
}

Abc!(T) abc(alias Fn, T)(T data) {
     static if (__traits(isTemplate, Fn))
         return new Abc!(T)(data, Fn!T);
     else
         return new Abc!(T)(data, Fn.toDelegate);
}

unittest {
     data_to_access_t  d;
     auto a = abc!((f) => writefln("test  %d", f.tacos))(d);
     auto b = abc!((data_to_access_t f) => writefln("test  %d", 
f.tacos))(d);
     a.execute();
     b.execute();
}

--
   Simen