How to avoid inout type constructor with Optional type wrapper undoing string type

[Ali Çehreli]

On 07/24/2018 02:47 AM, Timoses wrote:

 > Why does this fail while it works when replacing T with U in struct
 > W(T)?? It's so odd. Both T and U seem to resolve to "string".
 >
 >      struct W(T) {
 >          const T value;
 >          // Replacing `T value` with `U value` compiles
 >          this(U : T)(auto ref const T value) {

That means, "any U that can implicitly be converted to string". However, 
when U does not appear in the function parameter list, there is no way 
for the compiler to deduce U. (I don't think there is syntax to specify 
constructor template parameters explicitly.)

And if the parameter is always T, why is the constructor a template? Ok, 
perhaps U is used inside the constructor and the programmer needs to 
specify it... Still, I don't think there is such syntax.

Ali