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131 | -----------------------------------------------------------------------
-- util-nullables -- Basic types that can hold a null value
-- Copyright (C) 2017 Stephane Carrez
-- Written by Stephane Carrez (Stephane.Carrez@gmail.com)
--
-- Licensed under the Apache License, Version 2.0 (the "License");
-- you may not use this file except in compliance with the License.
-- You may obtain a copy of the License at
--
-- http://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS,
-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-- See the License for the specific language governing permissions and
-- limitations under the License.
-----------------------------------------------------------------------
with Ada.Calendar;
with Ada.Strings.Unbounded;
-- === Nullable types ===
-- Sometimes it is necessary to represent a simple data type with an optional boolean information
-- that indicates whether the value is valid or just null. The concept of nullable type is often
-- used in databases but also in JSON data representation. The <tt>Util.Nullables</tt> package
-- provides several standard type to express the null capability of a value.
--
-- By default a nullable instance is created with the null flag set.
package Util.Nullables is
use type Ada.Strings.Unbounded.Unbounded_String;
use type Ada.Calendar.Time;
DEFAULT_TIME : constant Ada.Calendar.Time;
-- ------------------------------
-- A boolean which can be null.
-- ------------------------------
type Nullable_Boolean is record
Value : Boolean := False;
Is_Null : Boolean := True;
end record;
Null_Boolean : constant Nullable_Boolean;
-- Return True if the two nullable times are identical (both null or both same value).
function "=" (Left, Right : in Nullable_Boolean) return Boolean is
(Left.Is_Null = Right.Is_Null and (Left.Is_Null or else Left.Value = Right.Value));
-- ------------------------------
-- An integer which can be null.
-- ------------------------------
type Nullable_Integer is record
Value : Integer := 0;
Is_Null : Boolean := True;
end record;
Null_Integer : constant Nullable_Integer;
-- Return True if the two nullable times are identical (both null or both same value).
function "=" (Left, Right : in Nullable_Integer) return Boolean is
(Left.Is_Null = Right.Is_Null and (Left.Is_Null or else Left.Value = Right.Value));
-- ------------------------------
-- A long which can be null.
-- ------------------------------
type Nullable_Long is record
Value : Long_Long_Integer := 0;
Is_Null : Boolean := True;
end record;
Null_Long : constant Nullable_Long;
-- Return True if the two nullable times are identical (both null or both same value).
function "=" (Left, Right : in Nullable_Long) return Boolean is
(Left.Is_Null = Right.Is_Null and (Left.Is_Null or else Left.Value = Right.Value));
-- ------------------------------
-- A string which can be null.
-- ------------------------------
type Nullable_String is record
Value : Ada.Strings.Unbounded.Unbounded_String;
Is_Null : Boolean := True;
end record;
Null_String : constant Nullable_String;
-- Return True if the two nullable times are identical (both null or both same value).
function "=" (Left, Right : in Nullable_String) return Boolean is
(Left.Is_Null = Right.Is_Null and (Left.Is_Null or else Left.Value = Right.Value));
-- ------------------------------
-- A date which can be null.
-- ------------------------------
type Nullable_Time is record
Value : Ada.Calendar.Time := DEFAULT_TIME;
Is_Null : Boolean := True;
end record;
Null_Time : constant Nullable_Time;
-- Return True if the two nullable times are identical (both null or both same time).
function "=" (Left, Right : in Nullable_Time) return Boolean is
(Left.Is_Null = Right.Is_Null and (Left.Is_Null or else Left.Value = Right.Value));
private
DEFAULT_TIME : constant Ada.Calendar.Time := Ada.Calendar.Time_Of (Year => 1901,
Month => 1,
Day => 2,
Seconds => 0.0);
Null_Boolean : constant Nullable_Boolean
:= Nullable_Boolean '(Is_Null => True,
Value => False);
Null_Integer : constant Nullable_Integer
:= Nullable_Integer '(Is_Null => True,
Value => 0);
Null_Long : constant Nullable_Long
:= Nullable_Long '(Is_Null => True,
Value => 0);
Null_String : constant Nullable_String
:= Nullable_String '(Is_Null => True,
Value => Ada.Strings.Unbounded.Null_Unbounded_String);
Null_Time : constant Nullable_Time
:= Nullable_Time '(Is_Null => True,
Value => DEFAULT_TIME);
end Util.Nullables;
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