Implicit conversion with ctor like C++

[Meta via Digitalmars-d-learn]

On Tuesday, 8 September 2015 at 19:23:47 UTC, Pierre wrote:
> Hi everybody,
>
> I would like to use implicit conversion like this:
>
> //Sample class
> class MyClass
> {
>    this(string MyValue){...}
> }
>
> //Called function
> void MyFunction(Foo MyFoo){}
>
> void main()
> {
>   MyFunction("Hello World!"); //Failed : MyFunction not 
> callable...
> }
>
> I saw in forum this is OK because D doesn't do implicit 
> conversion with ctor like C++
> But how can I do ? May I use alias ?
>
> Thank you for your attention.

No, as far as I know, D does not support implicit construction of 
classes or structs. There is *some* implicit conversion allowed, 
but in the opposite direction.

struct Test
{
     string s;
     alias s this;

     //Necessary for nice construction syntax
     this(string s) { this.s = s; }
}

void foo(string s)
{
     writeln(s);
}

void main()
{
     Test t = "asdf";
     foo(t); //Prints "asdf"
}

So with alias this, you can pass a Test to a function expecting a 
string, but not vice-versa.