.sort vs sort(): std.algorithm not up to the task?

[Stanislav Blinov via Digitalmars-d-learn]

On Thursday, 8 June 2017 at 01:57:47 UTC, Andrew Edwards wrote:
> Ranges may be finite or infinite but, while the destination may 
> be unreachable, we can definitely tell how far we've traveled. 
> So why doesn't this work?
>
> import std.traits;
> import std.range;
>
> void main()
> {
>     string[string] aa;
>
>     // what others have referred to as
>     // standard sort works but is deprecated
>     //auto keys = aa.keys.sort;
>
>     // Error: cannot infer argument types, expected 1 argument, 
> not 2
>     import std.algorithm: sort;
>     auto keys = aa.keys.sort();
>
>     // this works but why should I have to?
>     //import std.array: array;
>     //auto keys = aa.keys.sort().array;
>
>     foreach (i, v; keys){}
> }
>
> If I hand you a chihuahua for grooming, why am I getting back a 
> pit bull? I simply want a groomed chihuahua. Why do I need to 
> consult a wizard to get back a groomed chihuahua?

aa.keys.sort() should just work as is: aa.keys returns a 
string[], and that's a random access range that can be sorted. 
What exactly is the error?