singleton as mixin

[dlangBugzillaToGithub]

greeenify reported this on 2017-02-19T22:34:40Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=17203

Description

http://www.digitalmars.com/d/archives/digitalmars/D/The_singleton_design_pattern_in_D_C_and_Java_113474.html

would be nice to have this as a template mixin for simple reuse, e.g.

class Foo {
  mixin Singleton;
}