Explicit interface

A procedure must have an explicit interface in any of the following cases:

1. A reference to the procedure appears
   • with an argument keyword
   • as a defined assignment (for subroutines only)
   • in an expression as a defined operator (for functions only)
   • as a reference by its generic name
   • in a context that requires it to be pure
2. The procedure has
   • a dummy argument that has the ALLOCATABLE, OPTIONAL, POINTER, TARGET or VALUE attributes
   • a dummy argument that is polymorphic
   • an array-valued result (for functions only)
   • a result whose length type parameter is neither assumed nor constant (for character functions only)
   • a pointer or allocatable result (for functions only)
   • a dummy argument that is an assumed-shape array
3. The procedure is elemental.
4. The procedure has the BIND attribute.