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Ada Programming/Attributes

< Ada Programming

When entities like variables or subprograms are declared, certain properties thereof normally are left to the compiler to specify (like the size or the address of a variable, the calling convention of a subprogram). Properties which may be queried are called Attributes; those which may be specified are called Aspects. Aspects and attributes are defined in the Ada Reference Manual annex Annex K: Language-Defined Aspects and Attributes [Annotated].

Ada. Time-tested, safe and secure.
Ada. Time-tested, safe and secure.

Language summary attributes

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The concept of attributes is pretty unique to Ada. Attributes allow you to get —and sometimes set— information about objects or other language entities such as types. A good example is the Size attribute. It describes the size of an object or a type in bits. 

A : Natural := Integer'Size; -- A is now 32 (with the GNAT compiler for the x86 architecture)

However, unlike the sizeof operator from C/C++ the Size attribute can also be set: 

type Byte is range -128 .. 127;  -- The range fits into 8 bits but the
                                 -- compiler is still free to choose.
for  Byte'Size use 8;            -- Now we force the compiler to use 8 bits.

Of course not all attributes can be set. An attribute starts with a tick ' (apostrophe) and is followed by its name. The compiler determines by context if the tick is the beginning of an attribute, a character literal or a quantified expression. 

A : Character := Character'Val (32);     -- A is now a space
B : Character := ' ';                    -- B is also a space
S : String    := Character'(')')'Image;  -- an especially nice parsing exercise

List of language defined attributes

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Ada 2005
This is a new Ada 2005 attribute.
Ada 2012
This is a new Ada 2012 attribute.
Ada 2022
This is a new Ada 2022 attribute.
Obsolescent
This is a deprecated attribute and should not be used in new code.

A – B

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C

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D – F

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G – L

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M

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O – R

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S

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T – V

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W – Z

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List of implementation defined attributes

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The following attributes are not available in all Ada compilers, only in those that had implemented them.

Currently, there are only listed the implementation-defined attributes of a few compilers. You can help Wikibooks adding specific attributes of other compilers:

GNAT
Implementation-defined attribute of the GNAT compiler from AdaCore/FSF.
HP Ada
Implementation-defined attribute of the HP Ada compiler (formerly known as "DEC Ada").
ICC
Implementation-defined attribute[1] of the Irvine ICC compiler.
PowerAda
Implementation-defined attribute of OC Systems' PowerAda.
SPARCompiler
Implementation-defined attribute of Sun's SPARCompiler Ada.

A – D

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E – H

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I – N

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O – T

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U – Z

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See also

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Wikibook

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Ada Reference Manual

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Ada 83

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Ada 95

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Ada 2005

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Ada 2012

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Ada 2022

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References

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  1. ↑ "4.2 ICC-Defined Attributes", ICC Ada Implementation Reference — ICC Ada Version 8.2.5 for i960MC Targets, document version 2.11.4 [1]
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