J3/04-405r1 Date: 10 November 2004 To: J3 From: Van Snyder Subject: Interpretation request on type-bound generic interfaces Reference: 04-406r1 NUMBER: F03/0018 TITLE: Multiple identical specific procedures in type-bound generic interfaces KEYWORDS: Type-bound generics DEFECT TYPE: Clarification STATUS: QUESTION 1: Does the following program unit conform to the 2003 standard? module M type T contains procedure MyAdd generic :: operator(+) => myAdd end type T type X contains procedure, pass(b) :: MyAdd generic :: operator(+) => myAdd end type X contains integer function MyAdd ( A, B ) type(t), intent(in) :: A type(x), intent(in) :: B end function MyAdd end module M QUESTION 2: Does the following program unit conform to the 2003 standard? module M interface operator(+) procedure MyAdd end interface type T contains procedure MyAdd generic :: operator(+) => myAdd end type T contains integer function MyAdd ( A, B ) type(t), intent(in) :: A real, intent(in) :: B end function MyAdd end module M QUESTION 3: If the interface block and type definition are exchanged in QUESTION 2, does the program unit conform to the 2003 standard? ANALYSIS: The OPERATOR(+) bindings to the types T and X construct a single generic OPERATOR(+) interface that is a local entity of module M. They do not construct separate OPERATOR(+) generic interfaces that are separate local entities of the types. 16.2.3 (Restrictions on generic declarations) specifies that it "contains the rules that shall be satisfied by every pair of specific procedures that have the same generic identifier within a scoping unit." It is clear that if different functions with identical interfaces were bound to the types that they would be a "pair of specific procedures" and the resulting OPERATOR(+) interface would therefore be prohibited by 16.2.3. It is not clear whether the generic bindings bind separate specific procedures to the OPERATOR(+) generic, or only redundantly bind the same procedure. If the former, the program units are not standard conforming because they violate the provisions of 16.2.3. If the latter, they appear to be standard conforming. C1209 (in 12.3.2.1) prohibits a procedure to be bound to a generic interface more than once in a scoping unit, but only by way of a PROCEDURE statement in a generic interface block. There is nothing obviously equivalent in 4.5.4, nor anything that specifies that C1209 applies to generic bindings to types. It also does not apply between a generic interface block and a generic interface previously specified by a generic binding to a type (question 3), since the latter specific binding is accomplished by a conspiracy of a and a , not by a . ANSWER: The program units conform to the 2003 standard. Multiple bindings of the same procedure to a generic identifier using a in a type definition or by a type definition and a generic interface block do not bind a "pair of specific procedures" to the generic interface. Indeed, the following type definition is legal: type Z contains procedure :: MyAdd generic :: operator(+) => myAdd, operator(+) => myAdd end type Z An edit is provided to clarify this. EDITS: None. SUBMITTED BY: Van Snyder HISTORY: 04-405 m170 submitted 04-405r1 m170 passed J3 meeting