auto ref

[Mikhail Dahl]

On 16/12/2009 07:18, Walter Bright wrote:
> There's a need in generic code to have a function take a parameter by
> ref if it is an lvalue, and by value if it is an rvalue. This can be
> addressed by making it a template using auto ref:
>
> T foo(T)(auto ref T x) { ... }
>
> foo(3) // call by value
> int y;
> foo(y) // call by reference
>
> There is also a need to 'transmit' the ref'ness to the return value.
> This can be done with auto ref:
>
> auto ref foo(T)(auto ref T x) { return x; }
>
> foo(3) => int foo(int x)
> foo(y) => ref int foo(ref int x)
>
> This means that the generic forwarding function would look like:
>
> auto ref foo(alias F, T...)(auto ref T args) { return F(args); }

Just to confirm (I'm just getting into D, so I don't know much about the 
language, still learning), but the idea is to apply 'auto' not only to 
types but also to storage classes? As in 'automatically apply ref in the 
case of lvalue'?

If so I'm a little confused by 'auto ref foo(...' - if auto ref here is 
also simply an 'apply ref in the case of lvalue', then where is the 
return type being inferred from?

Dahl