Error: field r must be initialized in constructor, because it is nested struct

[Ali Çehreli via Digitalmars-d-learn]

Pretty standard thing doesn't work and I can't find it on bugzilla:

import std.algorithm;

struct Foo(R)
{
     R r;

     this(R r)    // <-- Compilation error
     {}
}

auto foo(R)(R r)
{
     return Foo!R(r);
}

void main()
{
     auto arr = [1];
     arr.map!(i => i).foo;
}

I was actually trying to dispatch the construction to a separate function:

     this(R r)    // <-- Still error
     {
         init(r);
     }

     void init(R r)
     {
         this.r = r;
     }

(I remember this latter issue having been discussed recently.)

Ali