Required Interfaces

Explicit interfaces are mandatory if an EXTERNAL procedure has:

• dummy arguments that are assumed-shape arrays, pointers or targets;
• OPTIONAL arguments;
• an array valued or pointer result (functions);
• a result that has an inherited LEN=* length specifier (character functions);

and when the reference:

• has a keyword argument;
• is a defined assignment;
• is a call to the generic name;
• is a call to a defined operator (functions).

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