Procedures that Require Explicit Interfaces

When a procedure is referenced, it must have an explicit interface in the following cases:

• If a reference to the procedure appears in one of the following:

  • An actual argument that is specified with a keyword

  • In a context that requires it to be PURE

• If the procedure has a dummy argument that is one of the following:

  • An object that has the ALLOCATABLE, ASYNCHRONOUS, OPTIONAL, POINTER, TARGET, VALUE, or VOLATILE attribute

  • An assumed-shape array

  • A polymorphic object (an object declared with a CLASS statement)

  • A coarray (an object declared with a CODIMENSION attribute or statement)

  • An object of a parameterized derived type

  • An object of assumed-rank or assumed-type

• If the procedure has any of the following:

  • A result that is an array, or a pointer, or is allocatable (functions only)

  • A result whose length is neither assumed nor a constant (character functions only)

• If a reference to the procedure appears as follows:

  • With an argument keyword

  • As a reference by its generic name

  • As a defined assignment (subroutines only)

  • In an expression as a defined operator (functions only)

  • In a context that requires it to be pure

• If the procedure is elemental

• If the procedure has the BIND attribute

Statement functions do not require an explicit interface.