---
import std.stdio;

void delegate() del;

abstract class A
{
    void f(int i)
    in { writeln("A.f.in: i = ", i); }
    body { } // no closure 

    void g(int i)
    in { writeln("A.g.in: i = ", i); }
    body { int x; del = { ++x; }; } // closure 
}

final class B: A
{
    override void f(int i)
    in { writeln("B.f.in: i = ", i); }
    body { int x; del = { ++x; }; } // closure appears

    override void g(int i)
    in { writeln("B.g.in: i = ", i); }
    body { } // closure disappears
}

void main()
{
    auto b = new B();
    b.f(107);
    b.g(108);
}
---

Output:
---
A.f.in: i = 909192741
A.g.in: i = 10428304
---

Also see Issue 6417.