Redefining := (was: The "()" operator revisited.)

[Jeffrey Carter <spam@spam.com>]

Robert A Duff wrote:

> It has to do with mutable record types (defaulted discrims).
> That's unfortunate; if you want to redefine ":=" for a non-mutable
> type, it's pretty annoying to be told you can't do that because
> mutable types exist in the language.

Could you do something like:

type Mutable (D : Natural := 0) is record
    ... -- whatever
end record;

type M2 is new Mutable;

procedure ":=" (To : out Mutable; From : in Mutable) is
    Result : M2 (D => From.D);

    procedure Assign (To : out M2; From : in M2) is
    begin -- Assign
       To := From;
       -- You can use default ":=" with M2 because it hasn't been
       -- redefined
    end Assign;
begin -- ":="
    -- Mess around with Result until it has what you want
    Assign (To => M2 (To), From => Result);
end ":=";

?

-- 
Jeff Carter
"I wave my private parts at your aunties."
Monty Python & the Holy Grail
13