confused about template constructors and implicit type conversions

[Basile B.]

On Wednesday, 4 December 2019 at 23:53:53 UTC, NeeO wrote:
> Would someone be able to explain this ? I can only seem to call 
> a template constructor in one way, but I can't seem to pass 
> what looks like an accepted type to the template constructor 
> via a function call.
>
> /+ main.d +/
> import std.stdio ;
>
> struct obj_ (T) {
>    int demo ;
>
>    this (int R,int C)(T[R][C] val) {
>       writeln ("init for type is ",val.init) ;
>       writeln ("num rows         ",R       ) ;
>       writeln ("num cols         ",C       ) ;
>    }
> }
> void check (obj_!float val) {
>    writeln ("success") ;
> }
>
> int main () {
>    float[3][4] testval ;
>    obj_!float  p = testval ; /+ works +/
>
>    check (testval) ; /+ not callable using argument types 
> compiler error +/
>    return 0 ;
> }

Hello, the problem you encounter here is that D, per spec, does 
not perform implicit construction from parameters. You have to 
constructs explicitly. Nothing more to explain.