Code shared from run.dlang.io.

main.d

import std;
alias section = void function(ulong s);
void bar(ulong s) {
    writefln("bar(%d)",s);
    return S(&bar)(s+1);
}
void baz(ulong s) {
    writefln("baz(%d)",s);
}
void quux(ulong s) {
    writefln("quux(%d)",s);
}
section S(section origin) {
    if (origin is &bar) return &baz;
    return null;
}
void main()
{
    writeln("Hello D");
    foo(iwrite!int, 123);
    int x = 1;
    foo((out int v){writefln("v=%s",v); v=234;},x);
    foo(iwrite!int, x);
    foo((ref int v){writefln("v=%s",v); v=345;},x);
    foo(iwrite!int, x);
    
    bar(1);
    foreach(i; 0..2) writefln("%d",i);
}

void foo(T)(void function(in T v) f,const T v) {
    //writefln("in v=%s",v);
    f(v); }
void foo(T)(void function(out T v) f, ref T v) {
    //writefln("out v=%s",v);
    f(v); }
void foo(T)(void function(ref T v) f, ref T v) {
    //writefln("mod v=%s",v);
    f(v); }
auto iwrite(T)() { return (in T v) {
    writefln("%s",v);
};}