CT-String as a Symbol

[Ali Çehreli via Digitalmars-d-learn]

On 04/15/2015 03:42 PM, "Nordlöw" wrote:

 > On Wednesday, 15 April 2015 at 20:12:27 UTC, Ali Çehreli wrote:
 >> Ali
 >
 > I cracked it:
 >
 > Reason: I hade a failing unittest using it as
 >
 >      auto xs = x.indexedBy!"I";
 >
 > which I changed to
 >
 >      auto xs = x.indexedBy!"Ix";
 >
 > For some reason the mixin magic becomes confused when I equals "I".
 >
 > Do you have any clues as to why?

That is because you have a nested struct named I inside IndexedBy. :) I 
print it with pragma(msg) below. So, mixin(I) is not happy because it 
thinks you mean 'struct I' :)

struct IndexedBy(R, string I = "Index") if (isArray!R)
{
     enum toMixin = q{ struct } ~ I ~
           q{ {
                   alias T = size_t;
                   this(T ix) { this._ix = ix; }
                   T opCast(U : T)() const { return _ix; }
                   private T _ix = 0;
               }
           };
     pragma(msg, toMixin);
     mixin(toMixin);

     mixin genOps!(mixin(I));
     R _r;
     alias _r this; // TODO Use opDispatch instead; to override only 
opSlice and opIndex
}

void main()
{
     auto i = IndexedBy!(int[], "I")();
}

The output:

  struct I {
                   alias T = size_t;
                   this(T ix) { this._ix = ix; }
                   T opCast(U : T)() const { return _ix; }
                   private T _ix = 0;
               }
 > Should we restrict IndexedBy to not allow I to equal "I"?

I don't think there is a general solution but you can always disallow as 
a template constraint or as a static assert:

struct IndexedBy(R, string I = "Index")
     if (isArray!R &&
         I != "I")    // <-- ADDED
{
     // ...
}

 >
 > :)
 >
 > Thx anyway.

Ali