Required Interfaces

Explicit interfaces are mandatory in the following situations.

1. the external procedure has dummy arguments that are assumed-shape arrays, pointers or targets. The compiler needs to figure out the rank, type and bounds of the array that need to be passed to the routine; pointers or targets. The compiler needs to figure out types and attributes that are to be transmitted to the procedure;
2. the external procedure has optional arguments; the compiler need to know the names of the arguments to figure out the correct association;
3. the external function returns an array or pointer valued result; the compiler needs to pass back info in a different form than usual;
4. the external character function contains an inherited LEN=* specifier; the compiler needs to know to pass string length info to and from the procedure;
5. the reference is a call to a generic name (extra info required);
6. the reference has a keyword argument (same reasons as for the optional case);
7. the reference is a defined assignment (extra info required);
8. the function reference is a call to a defined operator (extra info required);