Multiple return type or callback function

[Basile B. via Digitalmars-d-learn]

On Monday, 23 January 2017 at 15:15:35 UTC, aberba wrote:
> I'm creating a function to authenticate user login. I want to 
> determine login failure (Boolean) and error message (will be 
> sent to frontend) but D does have multiple return type
> [...]

Yes, MRV can be done with a tuple

auto foo()
{
     import std.typecons;
     return tuple(true, "123456");
}

void main(string[] args)
{
     auto auth = foo;
     if (auth[0])
         auth[1].writeln;
}

It's more or less like returning a Voldemort struct.