is this invalid code

[Daniel Davidson]

The following crashes on writeln, but looks reasonable. Is some 
form of initializing ctor required for RateCurve?

import std.datetime;
import std.range;
import std.stdio;
struct DateRate {
  Date date;
  double value = 0.0;
}

struct RateCurve {
  private immutable(DateRate)[] _data;
}

struct CFS {
  double initialValue;
  RateCurve growth;
}

void main() {
  auto s = CFS(1.0);
  // auto s = CFS(1.0, RateCurve()); // crashes
  // auto s = CFS(1.0, RateCurve([])); // works
  writeln(s);
}

Thanks
Dan