Is it possible to override the behaviour of to!string(x) when x is an enum. I'm asking because this

enum CxxRefQualifier
{
    none,
    normalRef,
    rvalueRef
}

string toString(CxxRefQualifier refQ) @safe pure nothrow
{
    final switch (refQ)
    {
        case CxxRefQualifier.none: return "";
        case CxxRefQualifier.normalRef: return "&";
        case CxxRefQualifier.rvalueRef: return "&&";
    }
}

doesn't affect behaviour of to!string(x) when x is an instance of CxxRefQualifier.

On Tuesday, 2 September 2014 at 12:54:55 UTC, Nordlöw wrote:
> Is it possible to override the behaviour of to!string(x) when x is an enum. I'm asking because this
>
> enum CxxRefQualifier
> {
>     none,
>     normalRef,
>     rvalueRef
> }
>
> string toString(CxxRefQualifier refQ) @safe pure nothrow
> {
>     final switch (refQ)
>     {
>         case CxxRefQualifier.none: return "";
>         case CxxRefQualifier.normalRef: return "&";
>         case CxxRefQualifier.rvalueRef: return "&&";
>     }
> }
>
> doesn't affect behaviour of to!string(x) when x is an instance of CxxRefQualifier.

i can think of two ways(both from memory)

1) specialized template override
template to(T: enum)(T s)
{
 string to(T s) { .. your custom code .. }
}

or just stringof
CxxRefQualifier crq = CxxRefQualifier.normalRef;
assert(crq == "normalRef");

sorry, i forgot everything.
here is example of how to do this
-----

import std.conv : to;

enum Test
{
 One,
 Two,
 Three,
}


template to(T: string)
{
 T to(A: Test)(A val)
 {
  final switch (val)
  {
   case Test.One: return "1";
   case Test.Two: return "2";
   case Test.Three: return "3";
  }
 }
}


void main()
{
assert(to!string(Test.One) == "1");
auto t = cast(Test)2;
assert(to!string(t) == "3");
assert(to!int("4") == 4); // shows original to! template works
}

On Tuesday, 2 September 2014 at 12:54:55 UTC, Nordlöw wrote:
> Is it possible to override the behaviour of to!string(x) when x is an enum. I'm asking because this
>
> enum CxxRefQualifier
> {
>     none,
>     normalRef,
>     rvalueRef
> }
>
> string toString(CxxRefQualifier refQ) @safe pure nothrow
> {
>     final switch (refQ)
>     {
>         case CxxRefQualifier.none: return "";
>         case CxxRefQualifier.normalRef: return "&";
>         case CxxRefQualifier.rvalueRef: return "&&";
>     }
> }
>
> doesn't affect behaviour of to!string(x) when x is an instance of CxxRefQualifier.

That won't work, because your "toString" is a free function. The module system doesn't allow this kind of "Koenig lookup"-like hijack. The only reason it allows for things like front/popFront and arrays, is that the other modules import std.array, and are "aware" of the functions. This is not true for user defined types. This may or may not be a feature :)

Unless we allow defining "enum-member functions", AFAIK, it is impossible to override the printing behavior for enums... short of injecting your own modules in std.format/std.conv. Or to have a parameter "moduleLookup" in said template functions.

On Tuesday, 2 September 2014 at 14:59:41 UTC, evilrat wrote:
> sorry, i forgot everything.
> here is example of how to do this
> -----
>
> import std.conv : to;
>
> enum Test
> {
>  One,
>  Two,
>  Three,
> }
>
>
> template to(T: string)
> {
>  T to(A: Test)(A val)
>  {
>   final switch (val)
>   {
>    case Test.One: return "1";
>    case Test.Two: return "2";
>    case Test.Three: return "3";
>   }
>  }
> }
>
>
> void main()
> {
> assert(to!string(Test.One) == "1");
> auto t = cast(Test)2;
> assert(to!string(t) == "3");
> assert(to!int("4") == 4); // shows original to! template works
> }

Word of warning: You are not overriding "to", but rather, simply defining your own "to" locally, which resolves as a better match in the context where you are using it.

If you pass the enum to another function in another module, your "to" will NOT be called.

On Tuesday, 2 September 2014 at 15:41:17 UTC, monarch_dodra wrote:
> Unless we allow defining "enum-member functions", AFAIK, it is impossible to override the printing behavior for enums...

... If your enum actually represents strings, then you could:

enum CxxRefQualifier : string
{
    none      = "",
    normalRef = "&",
    rvalueRef = "&&",
}

That in itself is not enough, but you *can* cast your enum to string, and then print that, or pass that.

See also:
https://issues.dlang.org/show_bug.cgi?id=11571

On Tuesday, 2 September 2014 at 15:42:36 UTC, monarch_dodra wrote:
>
> Word of warning: You are not overriding "to", but rather, simply defining your own "to" locally, which resolves as a better match in the context where you are using it.
>
> If you pass the enum to another function in another module, your "to" will NOT be called.

i know. and because of that this template in same scope as enum