As a language extension, the declaration of a generic formal function is
allowed to have a default given by an expression in parentheses, where
the expression is of the function's result type and can refer to formal
parameters of the function (in direct analogy with expression functions).
For example:
generic
type T is private;
with function Copy (Item : T) return T is (Item); -- Defaults to Item
package Stacks is
type Stack is limited private;
procedure Push (S : in out Stack; X : T); -- Calls Copy on X
function Pop (S : in out Stack) return T; -- Calls Copy to return item
private
...
end Stacks;
Tested on x86_64-pc-linux-gnu, committed on trunk
gcc/ada/
* doc/gnat_rm/implementation_defined_pragmas.rst: Add
documentation of the new form of formal subprogram default in
the section on language extensions (pragma Extensions_Allowed).
* gnat_rm.texi: Regenerate.
* gen_il-gen-gen_nodes.adb: Add Expression as a syntactic field
of N_Formal_(Abstract|Concrete)_Subprogram_Declaration nodes.
* par-ch12.adb (P_Formal_Subprogram_Declaration): Add parsing
support for the new default of a parenthesized expression for
formal functions. Issue an error when extensions are not
allowed, suggesting use of -gnatX. Update comment with extended
syntax for SUBPROGRAM_DEFAULT.
* sem_ch12.adb (Analyze_Formal_Subprogram_Declaration): Issue an
error when an expression default is given for an abstract formal
function. When a default expression is present for a formal
function, install the function's formals and preanalyze the
expression.
(Instantiate_Formal_Subprogram): Fix typo in RM paragraph in a
comment. When a formal function has a default expression,
create a body for the function that will evaluate the expression
and will be called when the default applies in an instantiation.
The implicit function is marked as inlined and as having
convention Intrinsic.diff --git a/gcc/ada/doc/gnat_rm/implementation_defined_pragmas.rst b/gcc/ada/doc/gnat_rm/implementation_defined_pragmas.rst
--- a/gcc/ada/doc/gnat_rm/implementation_defined_pragmas.rst
+++ b/gcc/ada/doc/gnat_rm/implementation_defined_pragmas.rst
@@ -2401,6 +2401,30 @@ of GNAT specific extensions are recognized as follows:
name, preference is given to the component in a selected_component
(as is currently the case for tagged types with such component names).
+* Expression defaults for generic formal functions
+
+ The declaration of a generic formal function is allowed to specify
+ an expression as a default, using the syntax of an expression function.
+
+ Here is an example of this feature:
+
+ .. code-block:: ada
+
+ generic
+ type T is private;
+ with function Copy (Item : T) return T is (Item); -- Defaults to Item
+ package Stacks is
+
+ type Stack is limited private;
+
+ procedure Push (S : in out Stack; X : T); -- Calls Copy on X
+
+ function Pop (S : in out Stack) return T; -- Calls Copy to return item
+
+ private
+ -- ...
+ end Stacks;
+
.. _Pragma-Extensions_Visible:
Pragma Extensions_Visible
diff --git a/gcc/ada/gen_il-gen-gen_nodes.adb b/gcc/ada/gen_il-gen-gen_nodes.adb
--- a/gcc/ada/gen_il-gen-gen_nodes.adb
+++ b/gcc/ada/gen_il-gen-gen_nodes.adb
@@ -1136,11 +1136,13 @@ begin -- Gen_IL.Gen.Gen_Nodes
Cc (N_Formal_Abstract_Subprogram_Declaration, N_Formal_Subprogram_Declaration,
(Sy (Specification, Node_Id),
Sy (Default_Name, Node_Id, Default_Empty),
+ Sy (Expression, Node_Id, Default_Empty),
Sy (Box_Present, Flag)));
Cc (N_Formal_Concrete_Subprogram_Declaration, N_Formal_Subprogram_Declaration,
(Sy (Specification, Node_Id),
Sy (Default_Name, Node_Id, Default_Empty),
+ Sy (Expression, Node_Id, Default_Empty),
Sy (Box_Present, Flag)));
Ab (N_Push_Pop_xxx_Label, Node_Kind);
diff --git a/gcc/ada/gnat_rm.texi b/gcc/ada/gnat_rm.texi
--- a/gcc/ada/gnat_rm.texi
+++ b/gcc/ada/gnat_rm.texi
@@ -3853,6 +3853,31 @@ simple name as one of the type’s primitive subprograms, where the
component is visible at the point of a selected_component using that
name, preference is given to the component in a selected_component
(as is currently the case for tagged types with such component names).
+
+@item
+Expression defaults for generic formal functions
+
+The declaration of a generic formal function is allowed to specify
+an expression as a default, using the syntax of an expression function.
+
+Here is an example of this feature:
+
+@example
+generic
+ type T is private;
+ with function Copy (Item : T) return T is (Item); -- Defaults to Item
+package Stacks is
+
+ type Stack is limited private;
+
+ procedure Push (S : in out Stack; X : T); -- Calls Copy on X
+
+ function Pop (S : in out Stack) return T; -- Calls Copy to return item
+
+private
+ -- ...
+end Stacks;
+@end example
@end itemize
@node Pragma Extensions_Visible,Pragma External,Pragma Extensions_Allowed,Implementation Defined Pragmas
diff --git a/gcc/ada/par-ch12.adb b/gcc/ada/par-ch12.adb
--- a/gcc/ada/par-ch12.adb
+++ b/gcc/ada/par-ch12.adb
@@ -1165,6 +1165,7 @@ package body Ch12 is
-- [ASPECT_SPECIFICATIONS];
-- SUBPROGRAM_DEFAULT ::= DEFAULT_NAME | <>
+ -- | ( EXPRESSION ) -- Allowed as extension (-gnatX)
-- DEFAULT_NAME ::= NAME | null
@@ -1219,6 +1220,29 @@ package body Ch12 is
Scan; -- past NULL
+ -- When extensions are enabled, a formal function can have a default
+ -- given by a parenthesized expression (expression function syntax).
+
+ elsif Token = Tok_Left_Paren then
+ Error_Msg_GNAT_Extension
+ ("expression default for formal subprograms");
+
+ if Nkind (Spec_Node) = N_Function_Specification then
+ Scan; -- past "("
+
+ Set_Expression (Def_Node, P_Expression);
+
+ if Token /= Tok_Right_Paren then
+ Error_Msg_SC ("missing "")"" at end of expression default");
+ else
+ Scan; -- past ")"
+ end if;
+
+ else
+ Error_Msg_SP
+ ("only functions can specify a default expression");
+ end if;
+
else
Set_Default_Name (Def_Node, P_Name);
end if;
diff --git a/gcc/ada/sem_ch12.adb b/gcc/ada/sem_ch12.adb
--- a/gcc/ada/sem_ch12.adb
+++ b/gcc/ada/sem_ch12.adb
@@ -3278,6 +3278,7 @@ package body Sem_Ch12 is
procedure Analyze_Formal_Subprogram_Declaration (N : Node_Id) is
Spec : constant Node_Id := Specification (N);
Def : constant Node_Id := Default_Name (N);
+ Expr : constant Node_Id := Expression (N);
Nam : constant Entity_Id := Defining_Unit_Name (Spec);
Subp : Entity_Id;
@@ -3310,6 +3311,18 @@ package body Sem_Ch12 is
("a formal abstract subprogram cannot default to null", Spec);
end if;
+ -- A formal abstract function cannot have an expression default
+ -- (expression defaults are allowed for nonabstract formal functions
+ -- when extensions are enabled).
+
+ if Nkind (Spec) = N_Function_Specification
+ and then Present (Expr)
+ then
+ Error_Msg_N
+ ("a formal abstract subprogram cannot default to an expression",
+ Spec);
+ end if;
+
declare
Ctrl_Type : constant Entity_Id := Find_Dispatching_Type (Nam);
begin
@@ -3336,7 +3349,7 @@ package body Sem_Ch12 is
if Box_Present (N) then
null;
- -- Else default is bound at the point of generic declaration
+ -- Default name is bound at the point of generic declaration
elsif Present (Def) then
if Nkind (Def) = N_Operator_Symbol then
@@ -3461,6 +3474,16 @@ package body Sem_Ch12 is
Error_Msg_N ("no visible subprogram matches specification", N);
end if;
end if;
+
+ -- When extensions are enabled, an expression can be given as default
+ -- for a formal function. The expression must be of the function result
+ -- type and can reference formal parameters of the function.
+
+ elsif Present (Expr) then
+ Push_Scope (Nam);
+ Install_Formals (Nam);
+ Preanalyze_Spec_Expression (Expr, Etype (Nam));
+ End_Scope;
end if;
<<Leave>>
@@ -11101,7 +11124,7 @@ package body Sem_Ch12 is
Make_Handled_Sequence_Of_Statements (Loc,
Statements => New_List (Make_Null_Statement (Loc))));
- -- RM 12.6 (16 2/2): The procedure has convention Intrinsic
+ -- RM 12.6 (16.2/2): The procedure has convention Intrinsic
Set_Convention (Defining_Unit_Name (New_Spec), Convention_Intrinsic);
@@ -11110,6 +11133,40 @@ package body Sem_Ch12 is
Set_Is_Inlined (Defining_Unit_Name (New_Spec));
return Decl_Node;
+ -- Handle case of a formal function with an expression default (allowed
+ -- when extensions are enabled).
+
+ elsif Nkind (Specification (Formal)) = N_Function_Specification
+ and then Present (Expression (Formal))
+ then
+ -- Generate body for function, for use in the instance
+
+ declare
+ Expr : constant Node_Id := New_Copy (Expression (Formal));
+ Stmt : constant Node_Id := Make_Simple_Return_Statement (Loc);
+ begin
+ Set_Sloc (Expr, Loc);
+ Set_Expression (Stmt, Expr);
+
+ Decl_Node :=
+ Make_Subprogram_Body (Loc,
+ Specification => New_Spec,
+ Declarations => New_List,
+ Handled_Statement_Sequence =>
+ Make_Handled_Sequence_Of_Statements (Loc,
+ Statements => New_List (Stmt)));
+ end;
+
+ -- RM 12.6 (16.2/2): Like a null procedure default, the function
+ -- has convention Intrinsic.
+
+ Set_Convention (Defining_Unit_Name (New_Spec), Convention_Intrinsic);
+
+ -- Inline calls to it when optimization is enabled
+
+ Set_Is_Inlined (Defining_Unit_Name (New_Spec));
+ return Decl_Node;
+
else
Error_Msg_Sloc := Sloc (Scope (Analyzed_S));
Error_Msg_NE
