[Issue 21401] New: Writelning a tuple ignores member's toString.

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21401

          Issue ID: 21401
           Summary: Writelning a tuple ignores member's toString.
           Product: D
           Version: D2
          Hardware: x86_64
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: jonathanilevi at gmail.com

With

```
struct X {
    string toString() {
        return "hi";
    }
}
```

`writeln( tuple(X()) );` prints `Tuple!(X)(const(X)())` not `Tuple!(X)("hi")`.

Stringing a tuple should use the toString of its members.

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