To: J3                                                     J3/25-109r1
From: generics
Subject: Edits for TEMPLATE construct
Date: 2025-February-18
References: 25-107, 25-108, 24-125r5, 24-126r4, 24-127r4

Introduction:
=============

This is the 3rd of 6 papers that provide edits for the approved syntax
for templates.

Section 1:
==========

* Append the following at the end of the clause from paper 25-108.


tt.3 The TEMPLATE construct

tt.3.1 Syntax for the TEMPLATE construct

A template contains declarations, specifications, and definitions that are
parameterized by deferred arguments. Public identifiers of a template are
made accessible to other scoping units by instantiation of the template
and refer to specifc instances of the entities created by the
instantiation.

Rtt10 <template> <<is>> <template-stmt>
                        [ <template-specification-part> ]
                        [ <template-subprogram-part> ]
                        <end-template-stmt>

Ctt28 (Rtt10) A <template> shall only appear in the <specification-part>
              of a main program or module.

Rtt11 <template-stmt> <<is>>
          TEMPLATE <template-name> ([<deferred-arg-name-list>])

Rtt12 <end-template-stmt> <<is>>  END TEMPLATE [<template-name>]


Ctt29 (Rtt12) If a <template-name> appears in the <end-template-stmt>,
              it shall be identical to the <template-name>
              specified in the <template-stmt>.

tt.3.2 Template specification part

Rtt13 <template-specification-part> <<is>>
          [ <use-stmt> ] ...
          [ <import-stmt> ] ...
          [ <template-declaration-construct> ] ...

Rtt14 <template-declaration-construct>
          <<is>> <template-specification-construct>
          <<or>> <deferred-arg-decl-stmt>
          <<or>> <requirement>
          <<or>> <template>

Rtt15 <template-specification-construct>
          <<is>> <access-stmt>
          <<or>> <derived-type-def>
          <<or>> <enum-def>
          <<or>> <enumeration-type-def>
          <<or>> <generic-stmt>
          <<or>> <instantiate-stmt>
          <<or>> <interface-block>
          <<or>> <intrinsic-stmt>
          <<or>> <procedure-declaration-stmt>
          <<or>> <type-declaration-stmt>

Ctt30 (Rtt15) If <type-declaration-stmt> is specified, PARAMETER shall
              appear as an <attr-spec>.

Ctt30+ (Rtt15) If <procedure-declaration-stmt> is specified, POINTER
               shall not appear.


{ The implicit mapping within a template scoping unit is the null mapping
  for all the letters - specified in the "misc edits" paper via a change
  to "8.7 Implicit statement". }

NOTE

    A template specification section cannot declare variables or procedure
    pointers.

tt.3.3 Template subprogram part

Rtt16 <template-subprogram-part> <<is>> <contains-stmt>
                                        [ <template-subprogram> ] ...

Rtt17 <template-subprogram>
          <<is>> <function-subprogram>
          <<or>> <subroutine-subprogram>
          <<or>> <templated-function-subprogram>
          <<or>> <templated-subroutine-subprogram>

tt.4 Templated procedures

A templated procedure is a template that defines a single
procedure which is accessible via instantiation.

{ Templated procedures are added to <internal-subprogram> and
  <module-subprogram> by the "misc edits" paper, and so can appear
  anywhere a normal procedure definition can appear. }

Rtt18 <templated-function-subprogram> <<is>>
          <templated-function-stmt>
          <templated-subprogram-specification-part>
          [<execution-part>]
          [<internal-subprogram-part>]
          <end-function-stmt>

Ctt31 (Rtt18) If a <function-name> appears in the <end-function-stmt>,
              it shall be identical to the <template-name>
              specified in the <templated-function-stmt>.

Rtt19 <templated-subroutine-subprogram> <<is>>
          <templated-subroutine-stmt>
          <templated-subprogram-specification-part>
          [<execution-part>]
          [<internal-subprogram-part>]
          <end-subroutine-stmt>

Ctt32 (Rtt19) If a <subroutine-name> appears in the <end-subroutine-stmt>,
              it shall be identical to the <template-name>
              specified in the <templated-subroutine-stmt>.

Ctt33 An internal templated procedure shall not contain an
      <internal-subprogram-part>.

Ctt34 The <internal-subprogram-part> of a templated procedure shall not
      contain a <templated-function-subprogram> or
      <templated-subroutine-subprogram>.


Rtt20 <templated-function-stmt> <<is>>
          [ <prefix> ] FUNCTION <template-name>
          ( <deferred-arg-name-list> ) ([<dummy-arg-list>])
          [<suffix>]

Rtt21 <templated-subroutine-stmt> <<is>>
         [ <prefix> ] SUBROUTINE <template-name>
         ( <deferred-arg-name-list> ) ([<dummy-arg-list>])
         [<proc-language-binding-spec>]

Rtt22 <templated-subprogram-specification-part> <<is>>
          [ <use-stmt> ] ...
          [ <import-stmt> ] ...
          [ <templated-subprogram-declaration-construct> ] ...

Rtt23 <templated-subprogram-declaration-construct>
          <<is>> <deferred-arg-decl-stmt>
          <<or>> <format-stmt>
          <<or>> <specification-construct>

Ctt35 In either <templated-function-stmt> or
      <templated-subroutine-stmt>, <prefix> shall include TEMPLATE.

tt.5 Restrictions on template definitions

Ctt36 A local variable or local procedure pointer declared anywhere
      within a template or templated subprogram shall not have the
      SAVE attribute.

Ctt37 A COMMON statement or EQUIVALENCE statement shall not appear
      anywhere within a template or templated subprogram.

Ctt38 A procedure referenced anywhere within a template or templated
      subprogram shall have an explicit interface.

NOTE 1

    Constraint Ctt38 expresses the notion of type-safety.  In particular,
    this allows a template implementation to be verified to be internally
    consistent.

NOTE 2

    Example of a TEMPLATE construct in a specification section.

    TEMPLATE iterate_tmpl(T, C, S)
       PRIVATE
       PUBLIC :: iterate
       DEFERRED TYPE :: T
       DEFERRED INTEGER, PARAMETER :: C
       DEFERRED INTERFACE
          SUBROUTINE S(x, i)
             TYPE(T), INTENT(INOUT) :: x
             INTEGER, INTENT(IN) :: i
          END SUBROUTINE
       END INTERFACE
    CONTAINS
       SUBROUTINE iterate(x)
          TYPE(T), INTENT(INOUT) :: x
          INTEGER :: i
          DO i = 1, C
             CALL S(x, i)
          END DO
       END SUBROUTINE iterate
    END TEMPLATE iterate_tmpl

    Alternative implementation for the above example using a templated
    procedure in a subprogram part.

    TEMPLATE SUBROUTINE iterate(T, C, S)(x)
       DEFERRED TYPE :: T
       DEFERRED INTEGER, PARAMETER :: C
       DEFERRED INTERFACE
          SUBROUTINE S(x, i)
             TYPE(T), INTENT(INOUT) :: x
             INTEGER, INTENT(IN) :: i
          END SUBROUTINE
       END INTERFACE

       TYPE(T), INTENT(INOUT) :: x
       INTEGER :: i
       DO i = 1, C
          CALL S(x, i)
       END DO

    END SUBROUTINE iterate


===END===