Support implicit conversion between types

[ilya-stromberg]

I have some code like this:

struct Foo
{
        this(int i)
        {
                //do something useful
        }
}
void bar(Foo f)
{
        //do something else
}

void main()
{
        Foo f = 5;//works
        
        bar(f);//works
        
        bar(Foo(5));//works
        
	bar(5);//Error: function app.bar (Foo f) is not callable using 
argument types (int)
}


D can't implicitly convert type "int" to type "Foo", but 
constructor "Foo(int)" exists. Explicit conversion works fine.
What should I do to support this convertion implicitly?