Keeping a record of this:

http://forum.dlang.org/thread/20130706211329.GA17171@quickfur.ath.cx

---
// Function to test if T is independently instantiable.
void f(T)() {
    T t;
}

void main() {
    int a = 42;
    struct S {
        int y;
        bool f() { return (a == 42); }
    }

    f!S();
}
---