UFCS with constructors

[qznc]

On Wednesday, 6 November 2013 at 11:04:05 UTC, bearophile wrote:
> import std.typecons: Typedef;
> alias Foo = Typedef!double;
> void main() {
>     auto a1 = Foo(1);
>     pragma(msg, typeof(a1));
>     auto a2 = 1.Foo;
>     pragma(msg, typeof(a2));
>     auto a3 = Foo(-1);
>     pragma(msg, typeof(a3));
>     auto a4 = -1.Foo;
>     pragma(msg, typeof(a4));
> }
>
>
> It prints:
>
> Typedef!(double, nan)
> Typedef!(double, nan)
> Typedef!(double, nan)
> double
>
>
> Is this expected/acceptable/good?

Operator precedence of "." is higher than unary minus. That 
should be the explanation, why the fourth output is different 
than the others.

However, what is Typedef for?