Auto ref function : How is this possible ?

[Steven Schveighoffer via Digitalmars-d-learn]

On 4/11/15 6:08 AM, matovitch wrote:
> Hi,
>
> I just learn about auto ref functions and tried this :
>
> import std.stdio;
>
> auto ref foo(int i, ref float f)
> {
>           if (i < f)
>           {
>               return i;
>           }
>           else
>           {
>               return f;
>           }
> }
>
> void main()
> {
>           int i = 1;
>           float f1 = 1.1;
>           float f2 = 0.9;
>           writeln(foo(i, f1));
>           writeln(foo(i, f2));
> }
>
> Tricky questions : Does it compiles ? If yes what does it do ?
> Then my question : How is this possible ?

D has great compile-time tools to examine what the compiler is doing.

A great feature of D for investigating compiler internals is pragma(msg, 
...). This prints at compile time some message (a string) that is based 
on the state at the time. For example:

void main()
{
          int i = 1;
          float f1 = 1.1;
          float f2 = 0.9;
          pragma(msg, typeof(foo(i, f1)).stringof); // prints what type 
foo returns
          auto x = foo(i, f2);
          pragma(msg, typeof(x).stringof); // same thing, but easier to 
understand.
}

result (prints while compiling):

float
float

-Steve