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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].
Language summary attributes
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
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
C
D – F
- 'Definite
- 'Delta
- 'Denorm
- 'Digits
- 'Emax (Obsolescent)
- 'Enum_Rep (Ada 2022)
- 'Enum_Val (Ada 2022)
- 'Exponent
- 'External_Tag
- 'Epsilon (Obsolescent)
- 'First
- 'First_Bit
- 'Floor
- 'Fore
- 'Fraction
G – L
- 'Has_Same_Storage (Ada 2012)
- 'Identity
- 'Image (Changed in Ada 2022)
- 'Index (Ada 2022)
- 'Input
- 'Large (Obsolescent)
- 'Last
- 'Last_Bit
- 'Leading_Part
- 'Length
M
- 'Machine
- 'Machine_Emax
- 'Machine_Emin
- 'Machine_Mantissa
- 'Machine_Overflows
- 'Machine_Radix
- 'Machine_Rounding (Ada 2005)
- 'Machine_Rounds
- 'Mantissa (Obsolescent)
- 'Max
- 'Max_Alignment_For_Allocation (Ada 2012)
- 'Max_Size_In_Storage_Elements
- 'Min
- 'Mod (Ada 2005)
- 'Model
- 'Model_Emin
- 'Model_Epsilon
- 'Model_Mantissa
- 'Model_Small
- 'Modulus
O – R
- 'Object_Size (Ada 2022)
- 'Old (Ada 2012)
- 'Output
- 'Overlaps_Storage (Ada 2012)
- 'Parallel_Reduce (Ada 2022)
- 'Partition_ID
- 'Pos
- 'Position
- 'Pred
- 'Preelaborate_Initialization (Ada 2022)
- 'Priority (Ada 2005)
- 'Put_Image (Ada 2022)
- 'Range
- 'Read
- 'Reduce (Ada 2022)
- 'Relative_Deadline (Ada 2022)
- 'Remainder
- 'Result (Ada 2012)
- 'Round
- 'Rounding
S
- 'Safe_Emax (Obsolescent)
- 'Safe_First
- 'Safe_Large (Obsolescent)
- 'Safe_Last
- 'Safe_Small (Obsolescent)
- 'Scale
- 'Scaling
- 'Signed_Zeros
- 'Size
- 'Small
- 'Storage_Pool
- 'Storage_Size
- 'Stream_Size (Ada 2005)
- 'Succ
T – V
W – Z
- 'Wide_Image (Changed in Ada 2022)
- 'Wide_Value
- 'Wide_Wide_Image (Ada 2005, changed in Ada 2022)
- 'Wide_Wide_Value (Ada 2005)
- 'Wide_Wide_Width (Ada 2005)
- 'Wide_Width
- 'Width
- 'Write
List of implementation defined attributes
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 attribute1] of the Irvine [ICC compiler.
PowerAda
Implementation-defined attribute of OC Systems' PowerAda.
SPARCompiler
Implementation-defined attribute of Sun's SPARCompiler Ada.
A – D
- 'Abort_Signal (GNAT)
- 'Address_Size (GNAT)
- 'Architecture (ICC)
- 'Asm_Input (GNAT)
- 'Asm_Output (GNAT)
- 'AST_Entry (GNAT, HP Ada)
- 'Atomic_Always_Lock_Free (GNAT)
- 'Bit (GNAT, HP Ada)
- 'Bit_Position (GNAT)
- 'CG_Mode (ICC)
- 'Code_Address (GNAT)
- 'Compiler_Key (SPARCompiler)
- 'Compiler_Version (GNAT, SPARCompiler)
- 'Constrained (GNAT)
- 'Declared (ICC)
- 'Default_Bit_Order (GNAT)
- 'Default_Scalar_Storage_Order (GNAT)
- 'Deref (GNAT)
- 'Descriptor_Size (GNAT)
- 'Dope_Address (SPARCompiler)
- 'Dope_Size (SPARCompiler)
E – H
- 'Elaborated (GNAT)
- 'Elab_Body (GNAT)
- 'Elab_Spec (GNAT)
- 'Elab_Subp_Body (GNAT)
- 'Emax (GNAT)
- 'Enabled (GNAT)
- 'Entry_Number (SPARCompiler)
- 'Enum_Rep (GNAT)
- 'Enum_Val (GNAT)
- 'Epsilon (GNAT)
- 'Exception_Address (ICC)
- 'Extended_Aft (PowerAda)
- 'Extended_Base (PowerAda)
- 'Extended_Digits (PowerAda)
- 'Extended_Fore (PowerAda)
- 'Extended_Image (PowerAda)
- 'Extended_Value (PowerAda)
- 'Extended_Width (PowerAda)
- 'Extended_Wide_Image (PowerAda)
- 'Extended_Wide_Value (PowerAda)
- 'Extended_Wide_Width (PowerAda)
- 'Fast_Math (GNAT)
- 'Finalization_Size (GNAT)
- 'Fixed_Value (GNAT)
- 'From_Any (GNAT)
- 'Has_Access_Values (GNAT)
- 'Has_Discriminants (GNAT)
- 'Has_Tagged_Values (GNAT)
- 'High_Word (ICC)
- 'Homogeneous (SPARCompiler)
I – N
- 'Img (GNAT)
- 'Initialized (GNAT)
- 'Integer_Value (GNAT)
- 'Invalid_Value (GNAT)
- 'Linear_Address (ICC)
- 'Large (GNAT)
- 'Library_Level (GNAT)
- 'Low_Word (ICC)
- 'Loop_Entry (GNAT)
- 'Machine_Size (GNAT, HP Ada)
- 'Mantissa (GNAT)
- 'Max_Integer_Size (GNAT)
- 'Max_Interrupt_Priority (GNAT)
- 'Max_Priority (GNAT)
- 'Maximum_Alignment (GNAT)
- 'Mechanism_Code (GNAT)
- 'Null_Parameter (GNAT, HP Ada)
O – T
- 'Object_Size (GNAT)
- 'Old (GNAT)
- 'Passed_By_Reference (GNAT)
- 'Pool_Address (GNAT)
- 'Range_Length (GNAT)
- 'Ref (SPARCompiler)
- 'Restriction_Set (GNAT)
- 'Result (GNAT)
- 'Round (GNAT)
- 'Safe_Emax (GNAT)
- 'Safe_Large (GNAT)
- 'Safe_Small (GNAT)
- 'Scalar_Storage_Order (GNAT)
- 'Simple_Storage_Pool (GNAT)
- 'Small (GNAT)
- 'Small_Denominator (GNAT)
- 'Small_Numerator (GNAT)
- 'Storage_Unit (GNAT)
- 'Stub_Type (GNAT)
- 'System_Allocator_Alignment (GNAT)
- 'Target (ICC)
- 'Target_Name (GNAT)
- 'Task_ID (SPARCompiler)
- 'Tick (GNAT)
- 'To_Address (GNAT)
- 'To_Any (GNAT)
- 'Type_Class (GNAT, HP Ada)
- 'TypeCode (GNAT)
- 'Type_Key (SPARCompiler)
U – Z
- 'UET_Address (GNAT)
- 'Unconstrained_Array (GNAT)
- 'Universal_Literal_String (GNAT)
- 'Unrestricted_Access (GNAT, ICC)
- 'Update (GNAT)
- 'VADS_Size (GNAT)
- 'Valid_Value (GNAT)
- 'Valid_Scalars (GNAT)
- 'Value_Size (GNAT)
- 'Wchar_T_Size (GNAT)
- 'Word_Size (GNAT)
See also
Wikibook
Ada 83
Ada 95
Ada 2005
Ada 2012
- 4.1.4: Attributes [Annotated]
- Annex K: (informative) Language-Defined Aspects and Attributes [Annotated]
Ada 2022
- 4.1.4: Attributes [Annotated]
- Annex K: (informative) Language-Defined Aspects and Attributes [Annotated]
References
- ↑ "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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