Ada '83 Language Reference Manual

Copyright 1980, 1982, 1983 owned by the United States Government. Direct reproduction and usage requests to the Ada Information Clearinghouse.

A. Predefined Language Attributes

Style Guide references: 3.2.5 Constants and Named Numbers, 3.4.2 Enumeration Types, 5.3.3 Private Types, 5.5.1 Range Values, 5.5.2 Array Attributes, 6.2.3 Attributes 'Count, 'Callable and 'Terminated, 8.2.4 Subtypes in Generic Specifications

This annex summarizes the definitions given elsewhere of the predefined language attributes.

P'ADDRESS
For a prefix P that denotes an object, a program unit, a label, or an entry:

                  Yields  the  address  of  the  first of the storage units
                  allocated to P.  For a subprogram, package, task unit, or
                  label, this value refers to the machine  code  associated
                  with  the  corresponding body or statement.  For an entry
                  for which an address clause has  been  given,  the  value
                  refers  to  the  corresponding  hardware  interrupt.  The
                  value of this attribute is of the type ADDRESS defined in
                  the package SYSTEM.  (See 13.7.2.)

P'AFT
For a prefix P that denotes a fixed point subtype:

                  Yields the number of  decimal  digits  needed  after  the
                  point  to  accommodate  the  precision  of the subtype P,
                  unless the delta of the subtype P is greater than 0.1, in
                  which case the attribute yields the value one.  (P'AFT is
                  the smallest positive integer N for which (10**N)*P'DELTA
                  is greater than or equal to  one.)   The  value  of  this
                  attribute   is   of  the  type  universal_integer.   (See
                  3.5.10.)

P'BASE
For a prefix P that denotes a type or subtype:

                  This attribute denotes the base type of P.   It  is  only
                  allowed  as  the prefix of the name of another attribute:
                  for example, P'BASE'FIRST.  (See 3.3.3.)

P'CALLABLE
For a prefix P that is appropriate for a task type:

                  Yields the value FALSE when the execution of the  task  P
                  is  either  completed  or terminated, or when the task is
                  abnormal;  yields the value TRUE otherwise.  The value of
                  this attribute is of the predefined type  BOOLEAN.   (See
                  9.9.)

P'CONSTRAINED
For a prefix P that denotes an object of a type with discriminants:

                  Yields  the  value  TRUE  if  a  discriminant  constraint
                  applies to the object P, or if the object is  a  constant
                  (including a formal parameter or generic formal parameter
                  of  mode in);  yields the value FALSE otherwise.  If P is
                  a generic formal parameter of mode in out, or if P  is  a
                  formal  parameter of mode in out or out and the type mark
                  given  in  the  corresponding   parameter   specification
                  denotes  an  unconstrained  type with discriminants, then
                  the value of this attribute is obtained from that of  the
                  corresponding   actual  parameter.   The  value  of  this
                  attribute  is  of  the  predefined  type  BOOLEAN.   (See
                  3.7.4.)

P'CONSTRAINED
For a prefix P that denotes a private type or subtype:

                  Yields  the  value  FALSE  if  P denotes an unconstrained
                  nonformal private type with discriminants;   also  yields
                  the  value  FALSE  if  P denotes a generic formal private   
                  type and the  associated  actual  subtype  is  either  an
                  unconstrained type with discriminants or an unconstrained
                  array  type;  yields the value TRUE otherwise.  The value
                  of this attribute is  of  the  predefined  type  BOOLEAN.
                  (See 7.4.2.)

P'COUNT
For a prefix P that denotes an entry of a task unit:

                  Yields  the number of entry calls presently queued on the
                  entry (if the attribute is  evaluated  within  an  accept
                  statement for the entry P, the count does not include the
                  calling  task).   The  value  of this attribute is of the
                  type universal_integer.  (See 9.9.)

P'DELTA
For a prefix P that denotes a fixed point subtype:

                  Yields the value of the  delta  specified  in  the  fixed
                  accuracy definition for the subtype P.  The value of this
                  attribute  is  of the type universal_real.  (See 3.5.10.)

P'DIGITS
For a prefix P that denotes a floating point subtype:

                  Yields the  number  of  decimal  digits  in  the  decimal
                  mantissa  of  model  numbers  of  the  subtype  P.  (This
                  attribute yields the number D  of  section  3.5.7.)   The
                  value of this attribute is of the type universal_integer.
                  (See 3.5.8.)

P'EMAX
For a prefix P that denotes a floating point subtype:

                  Yields the largest exponent value in the binary canonical
                  form  of model numbers of the subtype P.  (This attribute
                  yields the product 4*B of section 3.5.7.)  The  value  of
                  this  attribute  is  of the type universal_integer.  (See
                  3.5.8.)

P'EPSILON
For a prefix P that denotes a floating point subtype:

                  Yields the absolute value of the difference  between  the
                  model number 1.0 and the next model number above, for the
                  subtype  P.   The  value of this attribute is of the type
                  universal_real.  (See 3.5.8.)

P'FIRST
For a prefix P that denotes a scalar type, or a subtype of a scalar type:

                  Yields the lower bound of P.  The value of this attribute
                  has the same type as P.  (See 3.5.)

P'FIRST
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                  Yields  the  lower  bound  of the first index range.  The
                  value of this attribute has the same type as  this  lower
                  bound.  (See 3.6.2 and 3.8.2.)

P'FIRST(N)
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                  Yields  the  lower  bound  of  the N-th index range.  The
                  value of this attribute has the same type as  this  lower
                  bound.   The  argument  N  must be a static expression of
                  type universal_integer.  The value of N must be  positive
                  (nonzero)  and  no greater than the dimensionality of the
                  array.  (See 3.6.2 and 3.8.2.)

P'FIRST_BIT
For a prefix P that denotes a component of a record object:

                  Yields  the  offset,  from  the start of the first of the
                  storage units occupied by the component, of the first bit
                  occupied by the component.  This offset  is  measured  in
                  bits.   The  value  of  this  attribute  is  of  the type
                  universal_integer.  (See 13.7.2.)

P'FORE
For a prefix P that denotes a fixed point subtype:

                  Yields the minimum number of characters  needed  for  the
                  integer  part  of the decimal representation of any value
                  of the subtype P, assuming that the  representation  does
                  not  include  an  exponent,  but includes a one-character
                  prefix that is either a minus sign  or  a  space.   (This
                  minimum  number  does  not  include  superfluous zeros or
                  underlines, and is at least  two.)   The  value  of  this
                  attribute   is   of  the  type  universal_integer.   (See
                  3.5.10.)

P'IMAGE
For a prefix P that denotes a discrete type or subtype:

                  This  attribute  is  a  function with a single parameter.
                  The actual parameter X must be a value of the  base  type
                  of  P.   The  result  type is the predefined type STRING.
                  The result is the image of the value of  X,  that  is,  a
                  sequence  of characters representing the value in display
                  form.  The image of an integer value is the corresponding
                  decimal  literal;   without  underlines,  leading  zeros,
                  exponent,  or  trailing spaces;  but with a one character
                  prefix that is either a minus sign or a space. 

                  The  image  of  an  enumeration  value  is   either   the
                  corresponding   identifier   in   upper   case   or   the
                  corresponding  character  literal  (including   the   two
                  apostrophes);   neither  leading  nor trailing spaces are
                  included.  The image of a character other than a  graphic
                  character is implementation-defined.  (See 3.5.5.)

P'LARGE
For a prefix P that denotes a real subtype:

                  The attribute yields the largest positive model number of
                  the  subtype  P.   The  value of this attribute is of the  
                  type universal_real.  (See 3.5.8 and 3.5.10.)

P'LAST
For a prefix P that denotes a scalar type, or a subtype of a scalar type:

                  Yields the upper bound of P.  The value of this attribute
                  has the same type as P.  (See 3.5.)

P'LAST
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                  Yields  the  upper  bound  of the first index range.  The
                  value of this attribute has the same type as  this  upper
                  bound.  (See 3.6.2 and 3.8.2.)

P'LAST(N)
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                  Yields  the  upper  bound  of  the N-th index range.  The
                  value of this attribute has the same type as  this  upper
                  bound.   The  argument  N  must be a static expression of
                  type universal_integer.  The value of N must be  positive
                  (nonzero)  and  no greater than the dimensionality of the
                  array.  (See 3.6.2 and 3.8.2.)

P'LAST_BIT
For a prefix P that denotes a component of a record object:

                  Yields  the  offset,  from the start of the first of  the
                  storage units occupied by the component, of the last  bit
                  occupied by the component.  This  offset  is  measured in
                  bits.   The  value  of  this  attribute  is  of  the type
                  universal_integer.  (See 13.7.2.)

P'LENGTH
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                  Yields the number of values of the first index range
                  (zero  for  a  null  range).   The  value  of   this
                  attribute  is  of  the type universal_integer.  (See
                  3.6.2.)

P'LENGTH(N)
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                       Yields the number of values of the N-th index  range
                       (zero   for  a  null  range).   The  value  of  this
                       attribute is of  the  type  universal_integer.   The
                       argument  N  must  be  a  static  expression of type
                       universal_integer.  The value of N must be  positive
                       (nonzero)  and no greater than the dimensionality of
                       the array.  (See 3.6.2 and 3.8.2.)

P'MACHINE_EMAX
For a prefix P that denotes a floating point type or subtype:

                       Yields the largest value of exponent for the machine
                       representation of the base type of P.  The value  of
                       this  attribute  is  of  the type universal_integer.
                       (See 13.7.3.)

P'MACHINE_EMIN
For a prefix P that denotes a floating point type or subtype:

                       Yields  the  smallest  (most  negative)   value   of
                       exponent  for the machine representation of the base
                       type of P.  The value of this attribute  is  of  the
                       type universal_integer.  (See 13.7.3.)

P'MACHINE_MANTISSA
For a prefix P that denotes a floating point type or subtype:

                       Yields  the number of digits in the mantissa for the
                       machine representation of the base type  of  P  (the
                       digits  are  extended  digits  in  the  range  0  to
                       P'MACHINE_RADIX - 1).  The value of  this  attribute
                       is of the type universal_integer.  (See 13.7.3.)

P'MACHINE_OVERFLOWS
For a prefix P that denotes a real type or subtype:

                       Yields  the value TRUE if every predefined operation
                       on values of the base type of P  either  provides  a
                       correct    result,    or    raises   the   exception
                       NUMERIC_ERROR in overflow  situations;   yields  the
                       value  FALSE otherwise.  The value of this attribute
                       is of the predefined type BOOLEAN.  (See 13.7.3.)

P'MACHINE_RADIX
For a prefix P that denotes a floating point type or subtype:

                       Yields the value of the radix used  by  the  machine
                       representation  of the base type of P.  The value of
                       this attribute is  of  the  type  universal_integer.
                       (See 13.7.3.)

P'MACHINE_ROUNDS
For a prefix P that denotes a real type or subtype:

                       Yields the value TRUE if every predefined arithmetic
                       operation  on  values  of  the base type of P either
                       returns  an  exact  result  or  performs   rounding;
                       yields the value FALSE otherwise.  The value of this
                       attribute  is  of the predefined type BOOLEAN.  (See
                       13.7.3.)

P'MANTISSA
For a prefix P that denotes a real subtype:

                       Yields the number of binary  digits  in  the  binary
                       mantissa  of  model numbers of the subtype P.  (This
                       attribute yields the number B of section 3.5.7 for a
                       floating point type, or of section 3.5.9 for a fixed
                       point type.)  The value of this attribute is of  the
                       type universal_integer.  (See 3.5.8 and 3.5.10.)

P'POS
For a prefix P that denotes a discrete type or subtype:

                       This   attribute   is   a  function  with  a  single
                       parameter.  The actual parameter X must be  a  value
                       of  the base type of P.  The result type is the type
                       universal_integer.   The  result  is  the   position  
                       number  of  the value of the actual parameter.  (See
                       3.5.5.)

P'POSITION
For a prefix P that denotes a component of a record object:

                       Yields  the  offset,  from  the  start  of the first
                       storage unit occupied by the record, of the first of
                       the storage units occupied by the  component.   This
                       offset  is  measured in storage units.  The value of
                       this attribute is  of  the  type  universal_integer.
                       (See 13.7.2.)

P'PRED
For a prefix P that denotes a discrete type or subtype:

                       This   attribute   is   a  function  with  a  single
                       parameter.  The actual parameter X must be  a  value
                       of  the base type of P.  The result type is the base
                       type of P.  The result is the value  whose  position
                       number  is  one  less than that of X.  The exception
                       CONSTRAINT_ERROR is raised if X equals P'BASE'FIRST.
                       (See 3.5.5.)

P'RANGE
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                       Yields the first index range  of  P,  that  is,  the
                       range P'FIRST .. P'LAST.  (See 3.6.2.)

P'RANGE(N)
For a prefix P that is appropriate for an array type, or that denotes a constrained array subtype:

                       Yields the N-th index range of P, that is, the range
                       P'FIRST(N) .. P'LAST(N).  (See 3.6.2.)

P'SAFE_EMAX
For a prefix P that denotes a floating point type or subtype:

                       Yields the largest  exponent  value  in  the  binary
                       canonical  form  of safe numbers of the base type of
                       P.  (This attribute yields the number E  of  section
                       3.5.7.)   The value of this attribute is of the type
                       universal_integer.  (See 3.5.8.)

P'SAFE_LARGE
For a prefix P that denotes a real type or subtype:

                       Yields  the largest positive safe number of the base
                       type of P.  The value of this attribute  is  of  the
                       type universal_real.  (See 3.5.8 and 3.5.10.)

P'SAFE_SMALL
For a prefix P that denotes a real type or subtype:

                       Yields  the  smallest positive (nonzero) safe number
                       of the base type of P.  The value of this  attribute
                       is  of  the  type  universal_real.   (See  3.5.8 and
                       3.5.10.)

P'SIZE
For a prefix P that denotes an object:

                       Yields the number of  bits  allocated  to  hold  the
                       object.   The value of this attribute is of the type
                       universal_integer.  (See 13.7.2.)

P'SIZE
For a prefix P that denotes any type or subtype:

                       Yields the minimum number of bits that is needed  by
                       the  implementation  to  hold any possible object of
                       the type or subtype P.  The value of this  attribute 
                       is of the type universal_integer.  (See 13.7.2.)

P'SMALL
For a prefix P that denotes a real subtype:

                       Yields  the smallest positive (nonzero) model number
                       of the subtype P.  The value of this attribute is of
                       the type universal_real.  (See 3.5.8 and 3.5.10.)

P'STORAGE_SIZE
For a prefix P that denotes an access type or subtype:

                       Yields  the  total  number of storage units reserved
                       for the collection associated with the base type  of
                       P.   The  value  of  this  attribute  is of the type
                       universal_integer.  (See 13.7.2.)

P'STORAGE_SIZE
For a prefix P that denotes a task type or a task object:

                       Yields the number of storage units reserved for each
                       activation  of  a  task  of  the  type  P or for the
                       activation of the task object P.  The value of  this
                       attribute  is  of  the type universal_integer.  (See
                       13.7.2.)

P'SUCC
For a prefix P that denotes a discrete type or subtype:

                       This   attribute   is   a  function  with  a  single
                       parameter.  The actual parameter X must be  a  value
                       of  the base type of P.  The result type is the base  
                       type of P.  The result is the value  whose  position
                       number    is  one  greater  than  that  of  X.   The
                       exception CONSTRAINT_ERROR is  raised  if  X  equals
                       P'BASE'LAST.  (See 3.5.5.)

P'TERMINATED
For a prefix P that is appropriate for a task type:

                       Yields  the  value TRUE if the task P is terminated;
                       yields the value FALSE otherwise.  The value of this
                       attribute is of the predefined type  BOOLEAN.   (See
                       9.9.)

P'VAL
For a prefix P that denotes a discrete type or subtype:

                       This  attribute  is a special function with a single
                       parameter X which can be of any integer  type.   The
                       result  type  is  the base type of P.  The result is
                       the   value   whose   position   number    is    the
                       universal_integer  value  corresponding  to  X.  The
                       exception  CONSTRAINT_ERROR   is   raised   if   the
                       universal_integer value corresponding to X is not in
                       the range P'POS(P'BASE'FIRST) .. P'POS(P'BASE'LAST).
                       (See 3.5.5.)

P'VALUE
For a prefix P that denotes a discrete type or subtype:

                       This   attribute   is   a  function  with  a  single
                       parameter.  The actual parameter X must be  a  value
                       of  the  predefined type STRING.  The result type is
                       the base type of P.  Any leading  and  any  trailing
                       spaces   of   the   sequence   of   characters  that
                       corresponds to X  are ignored.    

                       For  an  enumeration  type,  if  the   sequence   of
                       characters  has the syntax of an enumeration literal
                       and if this literal exists for the base type  of  P,
                       the  result  is the corresponding enumeration value.
                       For an integer type, if the sequence  of  characters
                       has  the  syntax  of  an  integer  literal,  with an
                       optional single leading character that is a plus  or
                       minus sign, and if there is a corresponding value in
                       the  base  type  of P, the result is this value.  In
                       any other case, the  exception  CONSTRAINT_ERROR  is
                       raised.  (See 3.5.5.)

P'WIDTH
For a prefix P that denotes a discrete subtype:

                       Yields  the  maximum image length over all values of
                       the  subtype  P  (the  image  is  the  sequence   of
                       characters  returned  by  the attribute IMAGE).  The
                       value   of   this   attribute   is   of   the   type
                       universal_integer.  (See 3.5.5.)

Address any questions or comments to adainfo@sw-eng.falls-church.va.us.