• Pena (21/21) Feb 03 2015 I want to create a simple clone operator based on UDAs. First
• Kagamin (2/2) Feb 03 2015 Try variadic templates with recursion.
• thedeemon (14/17) Feb 03 2015 import std.traits, std.typetuple;

"Pena" <ttaipalus kapsi.fi> writes:

I want to create a simple clone operator based on UDAs. First
step is to create a tuple of the fields with desired UDA value
and construct a clone method which uses that tuple.

import std.traits;

enum Cloneable;

struct Foo {
     Cloneable int cloneableInt;
     Cloneable string cloneableStr;
    float notCloneable;
}


I came up with this to iterate through fields and print out ones
with  Cloneable set:

foreach(member; __traits(allMembers, Foo)) {
    foreach(attr; __traits(getAttributes, mixin(member))) {
      static if(is(attr == Cloneable)) {
        pragma(msg, member);
      }
    }
}

How can I use this code or something similar to dynamically
construct a tuple containing types of fields marked as  Cloneable?

"Kagamin" <spam here.lot> writes:

Try variadic templates with recursion.
For example see http://dpaste.dzfl.pl/f49a97e35974

"thedeemon" <dlang thedeemon.com> writes:

On Tuesday, 3 February 2015 at 10:32:47 UTC, Pena wrote:
 How can I use this code or something similar to dynamically
 construct a tuple containing types of fields marked as 
  Cloneable?

import std.traits, std.typetuple;

template CloneableTypes(S) {
   template IsCloneable(string M) {
     enum IsCloneable = staticIndexOf!(Cloneable, 
__traits(getAttributes, __traits(getMember, S, M))) >= 0;
   }

   template FieldType(string M) {
     alias FieldType = typeof(__traits(getMember, S, M));
   }

   alias CloneableTypes = staticMap!(FieldType, 
Filter!(IsCloneable, __traits(allMembers, S)));
}

Then CloneableTypes!Foo is a TypeTuple (int, string).