// https://issues.dlang.org/show_bug.cgi?id=16574 template Recursive(T) if (is(T == class)) { // fails because T is still forward referenced // speculative determineSize must not set type to error static assert (!__traits(compiles, { new T; })); // known size of class static assert (is(typeof(T.init) == T)); alias Recursive = T; } // must be resolvable class C { Recursive!C r; } template Recursive(T) if (is(T == struct)) { // fails because T is still forward referenced // speculative determineSize must not set type to error static assert (!__traits(compiles, { T t; })); // no size yet for struct static assert (!is(typeof(T.init))); alias Recursive = T*; } // must be resolvable struct S { Recursive!S r; }