Function Vec.opApply

int opApply (
  int delegate(size_t i, ref T) dg
) @system;

int opApply (
  int delegate(ref T) dg
) @system;

int opApply (
  @safe int delegate(size_t i, ref T) dg
) @safe;

int opApply (
  @safe int delegate(ref T) dg
) @safe;