Struct ctor called with cast

[ag0aep6g]

On 02/27/2018 09:30 PM, Radu wrote:
>>>>
> enum Type { a };
> struct S(Type t = Type.a)
> {
>      this(Type)(Type t)
>      {
>          import std.stdio;
>          writeln("ctor called.");
>      }
> }
> void main()
> {
>     auto x = S!(Type.a)(Type.a);
>     void* y = &x;
>     auto z = (cast(S!(Type.a)) y);
> }
>>>>
> 
> Surprisingly the cast will actually call the ctor. Is this to be 
> expected? Sure looks like a bug to me, as a non templated S will 
> complain about the cast.

Not a bug. The spec says [1]: "Casting a value v to a struct S, when 
value is not a struct of the same type, is equivalent to: S(v)"

Templates have nothing to do with it. Your code boils down to this:

----
struct S
{
     this(void* t)
     {
         import std.stdio;
         writeln("ctor called.");
     }
}
void main()
{
    void* y;
    auto z = cast(S) y;
}
----


[1] https://dlang.org/spec/expression.html#cast_expressions