Determining When Procedures Require Explicit Interfaces

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

• If the procedure has any of the following:
  
  
  • An optional dummy argument
    
    
  • A dummy argument that is an assumed-shape array, a pointer, or a target
    
    
  • A result that is array-valued or a pointer (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

For More Information:

• See Optional arguments.
• See Array arguments.
• See Pointer arguments.
• On argument keywords in subroutine references, see CALL.
• On argument keywords in function references, see Function references.
• See Pure procedures.
• See Elemental procedures.
• On user-defined generic procedures, see Defining Generic Names for Procedures.
• On defined operators, see Defining Generic Operators.
• On defined assignment, see Defining Generic Assignment.