Default initialization of structs?

[Gary Willoughby via Digitalmars-d-learn]

I have a struct where I need to perform default initialization of 
some members but the compiler doesn't allow to define a default 
constructor which allow optional arguments.

struct Foo(T)
{
     private int _bar;

     this(int bar = 1)
     {
         this._bar = bar;
     }
}

auto foo = Foo!(string) // error

Are there any patterns or idioms I could use to get the desired 
result? Or is it just the case if I use a constructor I have to 
pass values to it?