enum type changes according to context ?

[Jonathan M Davis]

On Thursday, March 28, 2013 16:02:18 Timothee Cour wrote:
> In code below, does transTable have a well defined type?
> it seems to change from line 9 (string[char])
> to line 10 (string[dchar])...
> 
> rdmd -version=bad main //CT erro
> rdmd main //works
> ----
> import std.string;
> void main(){
>     version(bad){
>         auto transTable = ['[' : `\[`];
>     }
>     else{
>         enum transTable = ['[' : `\[`];
>     }
>     pragma(msg,typeof(transTable)); //string[char] always
>     auto s = translate("[", transTable); //CT error with -version=bad only
> }
> ----
> 
> 
> Error: translate (string str, string[dchar] transTable, string
> toRemove = null) is not callable using argument types
> (string,string[char])

The key difference between the two transTables is that the first one creates a 
variable, whereas the second results in a value that gets copy-pasted wherever 
it gets used. So, the enum version should be the same as if you used the 
literal directly.

I believe that the version that the first one fails is because it defaults to 
char (because '[' will fit in a char) for the key and string for the value 
(since string literals default to string), and translate doesn't accept 
string[char].

The reason that the enum succeeds (as would a direct literal) is because the 
char literal can be inferred to be dchar in order to match the call that it's 
being passed to (so it's likely being passing a string[dchar]). The inferrence 
can occur in the enum case, because it's being used directly, whereas in the 
auto case, the literal's type has to be inferred before the translate call and 
therefore can't be inferred to match what translate would accept.

- Jonathan M Davis