Operators

Standard operators

Ada allows operator overloading for all standard operators and so the following summaries can only describe the suggested standard operations for each operator. It is quite possible to misuse any standard operator to perform something unusual.

Each operator is either a keyword or a delimiter—hence all operator pages are redirects to the appropriate keyword or delimiter.

Operators have arguments which in the RM are called Left and Right for binary operators, Right for unary operators (indicating the position with respect to the operator symbol).

The list is sorted from lowest precedence to highest precedence.

Logical operators

and
and ${\displaystyle x\land y}$, (also keyword and)
or
or ${\displaystyle x\lor y}$, (also keyword or)
xor
exclusive or ${\displaystyle (x\land {\bar {y}})\lor ({\bar {x}}\land y)}$, (also keyword xor)

Relational operators

/=
Not Equal ${\displaystyle x\neq y}$, (also special character /=)
=
Equal ${\displaystyle x=y}$, (also special character =)
<
Less than ${\displaystyle x, (also special character <)
<=
Less than or equal to (${\displaystyle x\leq y}$), (also special character <=)
>
Greater than (${\displaystyle x>y}$), (also special character >)
>=
Greater than or equal to (${\displaystyle x\geq y}$), (also special character >=)

+
Add ${\displaystyle x+y}$, (also special character +)
-
Subtract ${\displaystyle x-y}$, (also special character -)
&
Concatenate , ${\displaystyle x}$ & ${\displaystyle y}$, (also special character &)

+
Plus sign ${\displaystyle +x}$, (also special character +)
-
Minus sign ${\displaystyle -x}$, (also special character -)

Multiplying operator

*
Multiply, ${\displaystyle x\times y}$, (also special character *)
/
Divide ${\displaystyle x/y}$, (also special character /)
mod
modulus (also keyword mod)
rem
remainder (also keyword rem)

Highest precedence operator

**
Power ${\displaystyle x^{y}}$, (also special character **)
not
logical not ${\displaystyle \lnot x}$, (also keyword not)
abs
absolute value ${\displaystyle |x|}$ (also keyword abs)

Short-circuit control forms

These are not operators and thus cannot be overloaded.

and then
e.g. if Y /= 0 and then X/Y > Limit then ...
or else
e.g. if Ptr = null or else Ptr.I = 0 then ...

Membership tests

The Membership Tests also cannot be overloaded because they are not operators.

in
element of, ${\displaystyle var\in type}$, e.g. .mw-parser-output .ada-kw{background:none;border:none;padding:0;margin:0;color:DodgerBlue;font-weight:bold}.mw-parser-output .ada-kw a,.mw-parser-output .ada-kw a:visited{color:inherit}if I in Positive then, (also keyword in)
not in
not element of, ${\displaystyle var\notin type}$, e.g. if I not in Positive then, (also keywords not in)

Range membership test

if Today not in Tuesday .. Thursday then
...


Subtype membership test

Is_Non_Negative := X in Natural;


Class membership test

exit when Object in Circle'Class;


Range membership test

if Today not in Tuesday .. Thursday then
...


Choice list membership test

This language feature has been introduced in Ada 2012.

Ada 2012 extended the membership tests to include the union (short-circuit or) of several range or value choices.

if Today in Monday .. Wednesday | Friday then
...


Wikibook

 and and then > + abs & or or else >= - mod xor = < * rem in not /= <= ** / not in

Operators: &

As operator

Concatenating arrays

function "&" (Left, Right : T) return T;


Any array type (including fixed Strings) can be concatenated using the & operator. You can also append a single element to an array.

Common non-standard operations

Concatenating strings

The & operator is also defined for Bounded_String and Unbounded_String.

Operators: **

Operator

Standard Operations

Arithmetic Power of

The "**" operator is defined as arithmetic power of for all numeric types.

function "**" (Left : T; Right : Integer) return T;

Usage
A : constant Float   := 5.0 ** 2;  -- A is now 25.0
B : constant Integer := 5 ** 2;    -- B is also 25

Working Example
with Ada.Text_IO;

procedure Operator_Power is
A : constant Float   := 5.0 ** 2;  -- A is now 25.0
B : constant Integer := 5 ** 2;    -- B is also 25

package T_IO renames Ada.Text_IO;
package F_IO is new  Ada.Text_IO.Float_IO (Float);
package I_IO is new  Ada.Text_IO.Integer_IO (Integer);

begin
T_IO.Put ("A = ");
F_IO.Put (
Item => A,
Fore => 3,
Aft  => 1,
Exp  => 0);
T_IO.New_Line;
T_IO.Put ("B = ");
I_IO.Put (
Item  => B,
Width => 3,
Base  => 10);
T_IO.New_Line;
end Operator_Power;


Operators: *

Operator

Standard Operations

Arithmetic Multiplication

The "*" operator is defined as arithmetic multiplication for all numeric types.

function "*" (Left, Right : T) return T;

Usage
A : constant Float   := 5.0 * 2.0;  -- A is now 10.0
B : constant Integer := 5 * 2;      -- B is also 10

Working Example
with Ada.Text_IO;

procedure Operator_Multiply is
A : constant Float   := 5.0 * 2.0;  -- A is now 10.0
B : constant Integer := 5 * 2;      -- B is also 10

package T_IO renames Ada.Text_IO;
package F_IO is new  Ada.Text_IO.Float_IO (Float);
package I_IO is new  Ada.Text_IO.Integer_IO (Integer);

begin
T_IO.Put ("A = ");
F_IO.Put (
Item => A,
Fore => 3,
Aft  => 1,
Exp  => 0);
T_IO.New_Line;
T_IO.Put ("B = ");
I_IO.Put (
Item  => B,
Width => 3,
Base  => 10);
T_IO.New_Line;
end Operator_Multiply;


Common Non-Standard Operations

Character replication

A String is created where a single character is replicated n-times.

function "*" (Left : Natural; Right : Character) return String;


In addition to standard Strings this operator is also defined for Bounded_String and Unbounded_String.

Usage
A : constant String := 10 * 'X';  -- A is filled with 10 X

Working Example

The character replication operator is part of the Ada.Strings.Fixed package. You need to with and use the package to make the operator visible.

with Ada.Text_IO;
with Ada.Strings.Fixed;

procedure Operator_Multiply_2 is
use Ada.Strings.Fixed;

A : constant String := 10 * 'X';  -- A is filled with 10 X

package T_IO renames Ada.Text_IO;

begin
T_IO.Put_Line ("A = " & A);
end Operator_Multiply_2;


String replication

A String is created where a source string is replicated n-times.

function "*" (Left : Natural; Right : String) return String;


In addition to standard fixed strings this operator is also defined for Bounded_String and Unbounded_String.

Usage
A : constant String := 3 * "Hello ";  -- A is filled with 3 Hello

Working Example

The string replication operator is part of the Ada.Strings.Fixed package. You need to with and use the package to make the operator visible.

with Ada.Text_IO;
with Ada.Strings.Fixed;

procedure Operator_Multiply_3 is
use Ada.Strings.Fixed;

A : constant String := 3 * "Hello ";  -- A is filled with 3 Hello.

package T_IO renames Ada.Text_IO;

begin
T_IO.Put_Line ("A = " & A);
end Operator_Multiply_3;


Operators: -

Operator

Standard Operations

Arithmetic Subtraction

The "-" operator is defined as arithmetic subtraction for all numeric types.

function "-" (Left, Right : T) return T;

Usage
A : constant Float   := 5.0 - 2.0;  -- A is now 3.0
B : constant Integer := 5 - 2;      -- B is also 3


Minus sign

The "-" unary operator is defined as arithmetic negative sign for all numeric types.

function "-" (Left : T) return T;

Usage
A : constant Float   := -5.0;
B : constant Integer := -5;
C : constant Integer := -B;  -- C is now 5


Operators: /=

Operator

The operator /= compares two values on inequality. It is predefined for all non limited types. The operator will also be defined if a suitable operator = is available.

Note that in Ada the representation for this operator was chosen for resembling the mathematical symbol ${\displaystyle \neq }$, in the same way than <= resembles ${\displaystyle \leq }$, or >= resembles ${\displaystyle \geq }$.

Operators: /

Operator

Standard operations

Arithmetic division

The "/" operator is defined as arithmetic division for all numeric types.

function "/" (Left, Right : T) return T;

Usage
A : constant Float   := 5.0 / 2.0;  -- A is now 2.5
B : constant Integer := 5 / 2;      -- B is also 2


Operators: =

Operator

The operator = compares two values on equality. It is predefined for all non limited types.

Operators: abs

This keyword is used for the operator that gets the absolute value of a number.

y := abs x;


Operators: and

Logical operator

Boolean operator

X : Boolean := A > 10 and A < 20;


Boolean shortcut operator

Shortcut operators are used to make the evaluation of parts of boolean expressions conditional: and then, or else. This should never be done to speed up the evaluation (with modern optimizing compilers, it will possibly not have that effect). The correct use is to prevent the evaluation of expressions known to raise an exception.

if Dog /= null and then G (Dog) then
Walk (Dog);
end if;


In the example above, G (Dog) is only called when the pointer Dog is not null, i.e. it actually points to something.

Actually and then and or else are not operators in the sense of the reference manual, they are called 'Short-circuit Control Forms'. The difference is that (true) operators can be redefined (i.e. overloaded), whereas these cannot. They are however defined for any boolean type.

Since Ada allows parallel evaluation of the arguments for an expression, shortcut operators are not the standard way of evaluating boolean expressions. In any case where the final result of the evaluation is guaranteed to be the same, the compiler is allowed to use a shortcut evaluation.

Boolean operator on arrays

The and operator is applied to each pair of boolean elements from the left and right arrays. The result has the same bounds as the left operand.

type Day_Of_Month is range 1 .. 31;
type Month_Array is array (Day_Of_Month) of Boolean;

X : Month_Array := Function_1;
Y : Month_Array := Function_2;
Z : Month_Array := X and Y;


Bitwise operator

The operator and could be used with modular types to perform bitwise operations.

This language feature is only available from Ada 2005 on.

type Programmer is new Person
and Printable
with
record
Skilled_In : Language_List;
end record;


Operators: >=

Operator

The operator >= compares two values on greater than or equal to. It is predefined for all discrete types.

Operators: >

Operator

The operator > compares two values on being greater. It is predefined for all discrete types.

Operators: in

This keyword is used in:

Operators: <=

Operator

The operator <= compares two values on less than or equal to. It is predefined for all discrete types.

Operators: <

Operator

The operator < compares two values on less than. It is predefined for all discrete types.

Operators: mod

This keyword is used in the mod operator and in the declaration of modular types.

Operators: not

This keyword is used in:

Operators: or

Logical operator

Boolean operator

X : Boolean := A < 10 or A > 20;


Boolean shortcut operator

In the below example the function G is only called when F(X) returns the value False.

if F(X) or else G(Y) then

Walk_The_Dog;

end if;


This shortcut operator is sometimes used to speed up the evaluation of boolean expressions, but the Ada Style Guide recommends to compare the performance of both forms before switching one to the other. In general, it is good idea to use or else in sake of performance only when the second expression involves a function call.

The or else form is also used when the second expression is known to raise an exception unless the first expression is False.

Unlike C/C++, Ada short-cut operators are not the standard way to evaluate boolean expressions. This is because Ada is designed to do by default what is generally safer, but lets the programmer request a different behaviour.

Boolean operator on arrays

The or operator is applied to each pair of boolean elements from the left and right arrays. The result has the same bounds as the left operand.

type Day_Of_Month is range 1 .. 31;
type Month_Array is array (Day_Of_Month) of Boolean;

X : Month_Array := Function_1;
Y : Month_Array := Function_2;
Z : Month_Array := X or Y;


Bitwise operator

The operator or could be used with modular types to perform bitwise operations.

Operators: +

Operator

Standard Operations

The "+" operator is defined as arithmetic addition for all numeric types.

function "+" (Left, Right : T) return T;


Plus sign

The "+" operator is defined as arithmetic plus sign for all numeric types.

function "+" (Right : T) return T;

Usage
A : constant Float   := +5.0;  -- A is now 5.0
B : constant Integer := +5;    -- B is also 5


Common Non-Standard Operations

Type Conversion

The operator plus sign is often used to create a type conversion operator:

function "+" (Left : T1) return T2;


Operators: rem

Operator rem

The rem keyword is used as the remainder operator, that is, the remainder of the signed integer division. The following formula applies:

A = (A / B) * B + (A rem B)


Operators: xor

Logical operator

Boolean operator

X : Boolean := A = 10 xor B = 10;


Boolean operator on arrays

The xor operation is applied to each boolean inside the array.

type Day_Of_Month is range 1 .. 31;
type Month_Array is array (Day_Of_Month) of Boolean;

X : Month_Array := Function_1;
Y : Month_Array := Function_2;
Z : Month_Array := X xor Y;


Bitwise operator

The operator xor could be used with modular types and also with boolean arrays to perform bitwise operations.

Wikibook

Version 1.3, 3 November 2008 Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. <http://fsf.org/>

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This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

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Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.

11. RELICENSING

"Massive Multiauthor Collaboration Site" (or "MMC Site") means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A "Massive Multiauthor Collaboration" (or "MMC") contained in the site means any set of copyrightable works thus published on the MMC site.

"Incorporate" means to publish or republish a Document, in whole or in part, as part of another Document.

An MMC is "eligible for relicensing" if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3