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237 | with Ada.Exceptions;
private with Ada.Finalization;
generic
type Element_Type (<>) is private;
with function Image (This : Element_Type) return String;
package Optional.Values with Preelaborate is
-- Reference types
type Const_Ref (Ptr : access constant Element_Type) is
limited null record with Implicit_Dereference => Ptr;
type Var_Ref (Ptr : access Element_Type) is
limited null record with Implicit_Dereference => Ptr;
--------------
-- Optional --
--------------
type Optional is tagged private;
function "=" (L : Optional; R : Element_Type) return Boolean with
Post => "="'Result = (L.Has_Element and then L.Element = R);
function "=" (L : Element_Type; R : Optional) return Boolean with
Post => "="'Result = (R = L);
Empty : constant Optional;
function Has_Element (This : Optional) return Boolean;
function Is_Empty (This : Optional) return Boolean with
Post => Is_Empty'Result = not This.Has_Element;
function Image (This : Optional) return String;
-- Returns [empty] or [value: Element_Type'Image (This.Element)]
function Unit (Element : Element_Type) return Optional with
Post => Unit'Result.Element = Element;
function Element (This : Optional) return Const_Ref
with Pre => This.Has_Element;
function Value (This : Optional) return Element_Type
with Pre => This.Has_Element;
function Reference (This : in out Optional) return Var_Ref
with Pre => This.Has_Element;
----------------
-- Operations --
----------------
function Flat_Map
(This : Optional;
Mapper : access function (Element : Optional) return Optional)
return Optional with
Post => (if This.Has_Element and then Mapper /= null then
Flat_Map'Result = Mapper (This)
elsif This.Has_Element and then Mapper = null then
Flat_Map'Result = This
else
Flat_Map'Result = Empty);
function Map (This : Optional;
Mapper : access function (Element : Element_Type)
return Element_Type)
return Optional with
Post => (if This.Has_Element and then Mapper /= null then
Map'Result.Element.Ptr.all = Mapper (This.Element.Ptr.all)
elsif This.Has_Element and then Mapper = null then
Map'Result = This
else
Map'Result = Empty);
function Or_Else (This : Optional;
Default : Element_Type)
return Element_Type with
Post => (if This.Has_Element
then Or_Else'Result = This.Element.Ptr.all
else Or_Else'Result = Default);
function Or_Raise (This : Optional;
Ex_Id : Ada.Exceptions.Exception_Id;
Ex_Msg : String := "")
return Element_Type with
Post => (if This.Has_Element
then Or_Raise'Result = This.Element.Ptr.all
else raise Constraint_Error);
-- Actually, Ex_Id will be raised, not CE
function Filter (This : Optional;
Condition : Boolean) return Optional with
Post => (if Condition
then Filter'Result = This
else Filter'Result = Empty);
----------------
-- References --
----------------
function Image (This : Const_Ref) return String;
function Image (This : Var_Ref) return String;
private
package AF renames Ada.Finalization;
type Element_Access is access Element_Type;
type Optional is new Ada.Finalization.Controlled
with record
Element : Element_Access; -- Holders still causing bugs
end record;
overriding procedure Adjust (This : in out Optional);
overriding procedure Finalize (This : in out Optional);
---------
-- "=" --
---------
function "=" (L : Optional; R : Element_Type) return Boolean
is (L.Has_Element and then L.Element.all = R);
function "=" (L : Element_Type; R : Optional) return Boolean
is (R = L);
-------------
-- Element --
-------------
function Element (This : Optional) return Const_Ref
is (Const_Ref'(Ptr => This.Element));
Empty : constant Optional := (AF.Controlled with Element => null);
------------
-- Filter --
------------
function Filter (This : Optional;
Condition : Boolean) return Optional
is (if Condition
then This
else Empty);
--------------
-- Flat_Map --
--------------
function Flat_Map
(This : Optional;
Mapper : access function (Element : Optional) return Optional)
return Optional
is (if This.Has_Element and then Mapper /= null
then Mapper (This)
else This);
-----------------
-- Has_Element --
-----------------
function Has_Element (This : Optional) return Boolean
is (This.Element /= null);
-----------
-- Image --
-----------
function Image (This : Optional) return String
is (if not This.Has_Element
then "[empty]"
else "[value:"
& Image (This.Element.all) & "]");
function Image (This : Const_Ref) return String
is (Image (This.Ptr.all));
function Image (This : Var_Ref) return String
is (Image (This.Ptr.all));
--------------
-- Is_Empty --
--------------
function Is_Empty (This : Optional) return Boolean
is (not This.Has_Element);
---------
-- Map --
---------
function Map (This : Optional;
Mapper : access function (Element : Element_Type)
return Element_Type)
return Optional
is (if This.Has_Element and then Mapper /= null
then Unit (Mapper (This.Element.all))
else This);
-------------
-- Or_Else --
-------------
function Or_Else (This : Optional;
Default : Element_Type)
return Element_Type
is (if This.Has_Element
then This.Element.all
else Default);
---------------
-- Reference --
---------------
function Reference (This : in out Optional) return Var_Ref
is (Var_Ref'(Ptr => This.Element));
----------
-- Unit --
----------
function Unit (Element : Element_Type) return Optional
is (Ada.Finalization.Controlled with
Element => new Element_Type'(Element));
-----------
-- Value --
-----------
function Value (This : Optional) return Element_Type
is (Element (This));
end Optional.Values;
|