How to create delegates with an independent scope?

[Vijay Nayar]

Consider the following code example:

```d
import std.stdio;

void main()
{
   alias DelegateT = string delegate();

   // An array of delegates, each has their own scope.
   DelegateT[] funcs;
   foreach (i; ["ham", "cheese"]) {
     // Deliberately create a copy to keep in delegate scope.
     string myStr = i.dup;
     // The delegate will hopefully carry this copy around in its 
own scope.
     funcs ~= (() => myStr ~ " sandwich");
   }
	
   foreach (f; funcs) {
     writeln(f());
   }
}
```

The expected output is: "ham sandwich" and then "cheese sandwich".

The actual output is: "cheese sandwich" and then "cheese 
sandwich".

It seems that the variable `myStr` is in a sort of shared scope 
for both functions in the array, and the last value written to it 
dominates.

How do I create a delegate that acts like a 
[closure](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Closures), that is, it carries with it the environment in which it was created?