How do I get the value cache()?

[Marc via Digitalmars-d-learn]

let's assume I have

class C {
  static string foo() { writeln("got called!"); //.... }
}

then I want to cache foo at some point:

import std.algorithm;
auto v = cache(c.foo);

I call do:

for(int i = 0; i <10; i++) {
writeln(v);
}

then it'll print "got called"  only once, which is what I want 
but something obvious is how do I get the returned value as a 
string?
here's why I'm confused more often than I should: I geeeting to 
D's way to do thing and the auto keyword even in documentation 
confused me a bit as I'm used to C++/C# world where the 
struct/class returned is explicity so I just navigate to 
aggregate type's documentation page.