RM 4.5.3 (28) specifies that (except for records and limited types) a
membership operation uses the predefined equality, regardless of whether
user-defined equality for the type is available. This can be confusing
and deserves a new warning.
Compiling code.adb must yield:
code.adb:19:42: warning: membership test on "Var" uses predefined equality
code.adb:19:42: warning: even if user-defined equality exists
(RM 4.5.2 (28.1/3)
--
with Ada.Characters.Handling;
with Ada.Text_IO; use Ada.Text_IO;
procedure Code is
type Var is new Character;
function "=" (C1, C2 : Var) return Boolean;
function "=" (C1, C2 : Var) return Boolean is
use Ada.Characters.Handling;
begin
return To_Lower (Character (C1)) = To_Lower (Character (C2));
end "=";
V : Var := 'A';
begin
Put_Line ("equal " & Boolean'Image (V = 'a'));
Put_Line ("in " & Boolean'Image (V in 'a' | 'o'));
end Code;
Tested on x86_64-pc-linux-gnu, committed on trunk
2017-12-15 Ed Schonberg <[email protected]>
* sem_res.adb (Resolve_Membership_Op): Add warning on a membership
operation on a scalar type for which there is a user-defined equality
operator.
Index: sem_res.adb
===================================================================
--- sem_res.adb (revision 255694)
+++ sem_res.adb (working copy)
@@ -9086,6 +9086,21 @@
end loop;
end;
end if;
+
+ -- RM 4.5.2 (28.1/3) specifies that for types other than records or
+ -- limited types, evaluation of a membership test uses the predefined
+ -- equality for the type. This may be confusing to users, and the
+ -- following warning appears useful for the most common case.
+
+ if Is_Scalar_Type (Ltyp)
+ and then Present (Get_User_Defined_Eq (Ltyp))
+ then
+ Error_Msg_NE
+ ("membership test on& uses predefined equality?", N, Ltyp);
+ Error_Msg_N
+ ("\even if user-defined equality exists (RM 4.5.2 (28.1/3)?", N);
+ end if;
+
end Resolve_Set_Membership;
-- Start of processing for Resolve_Membership_Op
