# Annex K. Language-Defined Attributes

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This annex summarizes the definitions given elsewhere of the language-defined attributes.

- P'Access
- For a prefix P that denotes a subprogram:

- P'Access yields an access value that designates the subprogram denoted by P. The type of P'Access is an access-to-subprogram type (
*S*), as determined by the expected type. See 3.10.2.

- X'Access
- For a prefix X that denotes an aliased view of an object:

- X'Access yields an access value that designates the object denoted by X. The type of X'Access is an access-to-object type, as determined by the expected type. The expected type shall be a general access type. See 3.10.2.

- X'Address
- For a prefix X that denotes an object, program unit, or label:

- Denotes the address of the first of the storage elements allocated to X. For a program unit or label, this value refers to the machine code associated with the corresponding body or statement. The value of this attribute is of type System.Address. See 13.3.

- S'Adjacent
- For every subtype S of a floating point type
*T*:

- S'Adjacent denotes a function with the following specification:

```
function S'Adjacent (X, Towards : T)
return T
```

- If
*Towards*=*X*, the function yields*X*; otherwise, it yields the machine number of the type*T*adjacent to*X*in the direction of*Towards*, if that machine number exists. If the result would be outside the base range of S, Constraint_Error is raised. When*T'*Signed_Zeros is True, a zero result has the sign of*X*. When*Towards*is zero, its sign has no bearing on the result. See A.5.3.

- S'Aft
- For every fixed point subtype S:

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

- X'Alignment
- For a prefix X that denotes a subtype or object:

- The Address of an object that is allocated under control of the implementation is an integral multiple of the Alignment of the object (that is, the Address modulo the Alignment is zero). The offset of a record component is a multiple of the Alignment of the component. For an object that is not allocated under control of the implementation (that is, one that is imported, that is allocated by a user-defined allocator, whose Address has been specified, or is designated by an access value returned by an instance of Unchecked_Conversion), the implementation may assume that the Address is an integral multiple of its Alignment. The implementation shall not assume a stricter alignment.

- The value of this attribute is of type
*universal_integer*, and nonnegative; zero means that the object is not necessarily aligned on a storage element boundary. See 13.3.

- S'Base
- For every scalar subtype S:

- S'Base denotes an unconstrained subtype of the type of S. This unconstrained subtype is called the
*base subtype*of the type. See 3.5.

- S'Bit_Order
- For every specific record subtype S:

- Denotes the bit ordering for the type of S. The value of this attribute is of type System.Bit_Order. See 13.5.3.

- P'Body_Version
- For a prefix P that statically denotes a program unit:

- Yields a value of the predefined type String that identifies the version of the compilation unit that contains the body (but not any subunits) of the program unit. See E.3.

- T'Callable
- For a prefix T that is of a task type (after any implicit dereference):

- Yields the value True when the task denoted by T is
*callable*, and False otherwise; See 9.9.

- E'Caller
- For a prefix E that denotes an entry_declaration:

- Yields a value of the type Task_ID that identifies the task whose call is now being serviced. Use of this attribute is allowed only inside an entry_body or accept_statement corresponding to the entry_declaration denoted by E. See C.7.1.

- S'Ceiling
- For every subtype S of a floating point type
*T*:

- S'Ceiling denotes a function with the following specification:

```
function S'Ceiling (X : T)
return T
```

- The function yields the value
*Ceiling*(*X*), i.e., the smallest (most negative) integral value greater than or equal to*X*. When*X*is zero, the result has the sign of*X*; a zero result otherwise has a negative sign when S'Signed_Zeros is True. See A.5.3.

- S'Class
- For every subtype S of an untagged private type whose full view is tagged:

- Denotes the class-wide subtype corresponding to the full view of S. This attribute is allowed only from the beginning of the private part in which the full view is declared, until the declaration of the full view. After the full view, the Class attribute of the full view can be used. See 7.3.1.

- S'Class
- For every subtype S of a tagged type
*T*(specific or class-wide):

- S'Class denotes a subtype of the class-wide type (called
*T'*Class in this International Standard) for the class rooted at*T*(or if S already denotes a class-wide subtype, then S'Class is the same as S).

- S'Class is unconstrained. However, if S is constrained, then the values of S'Class are only those that when converted to the type
*T*belong to S. See 3.9.

- X'Component_Size
- For a prefix X that denotes an array subtype or array object (after any implicit dereference):

- Denotes the size in bits of components of the type of X. The value of this attribute is of type
*universal_integer*. See 13.3.

- S'Compose
- For every subtype S of a floating point type
*T*:

- S'Compose denotes a function with the following specification:

```
function S'Compose (Fraction : T;
Exponent : universal_integer)
return T
```

- Let
*v*be the value*Fraction*·*T***Machine_Radix**^{}**Exponent**Model_Small, the function yields*-*k*, where*k*is the normalized exponent of*Fraction*. If*v*is a machine number of the type*T*, or if |*v*| >=*T*v*; otherwise, it yields either one of the machine numbers of the type*T*adjacent to*v*. Constraint_Error is optionally raised if*v*is outside the base range of S. A zero result has the sign of*Fraction*when S'Signed_Zeros is True. See A.5.3.

- A'Constrained
- For a prefix A that is of a discriminated type (after any implicit dereference):

- Yields the value True if A denotes a constant, a value, or a constrained variable, and False otherwise. See 3.7.2.

- S'Copy_Sign
- For every subtype S of a floating point type
*T*:

- S'Copy_Sign denotes a function with the following specification:

```
function S'Copy_Sign (Value, Sign : T)
return T
```

- If the value of
*Value*is nonzero, the function yields a result whose magnitude is that of*Value*and whose sign is that of*Sign*; otherwise, it yields the value zero. Constraint_Error is optionally raised if the result is outside the base range of S. A zero result has the sign of*Sign*when S'Signed_Zeros is True. See A.5.3.

- E'Count
- For a prefix E that denotes an entry of a task or protected unit:

- Yields the number of calls presently queued on the entry E of the current instance of the unit. The value of this attribute is of the type
*universal_integer*. See 9.9.

- S'Definite
- For a prefix S that denotes a formal indefinite subtype:

- S'Definite yields True if the actual subtype corresponding to S is definite; otherwise it yields False. The value of this attribute is of the predefined type Boolean. See 12.5.1.

- S'Delta
- For every fixed point subtype S:

- S'Delta denotes the
*delta*of the fixed point subtype S. The value of this attribute is of the type*universal_real*. See 3.5.10.

- S'Denorm
- For every subtype S of a floating point type
*T*:

- Yields the value True if every value expressible in the form
- ±
*mantissa*·*T***Machine_Radix**^{}**T**Machine_Emin - where
*mantissa*is a nonzero*T***Machine_Mantissa-digit fraction in the number base****T**Machine_Radix, the first digit of which is zero, is a machine number (see 3.5.7) of the type*T*; yields the value False otherwise. The value of this attribute is of the predefined type Boolean. See A.5.3.

- S'Digits
- For every decimal fixed point subtype S:

- S'Digits denotes the
*digits*of the decimal fixed point subtype S, which corresponds to the number of decimal digits that are representable in objects of the subtype. The value of this attribute is of the type*universal_integer*. See 3.5.10.

- S'Digits
- For every floating point subtype S:

- S'Digits denotes the requested decimal precision for the subtype S. The value of this attribute is of the type
*universal_integer*. See 3.5.8.

- S'Exponent
- For every subtype S of a floating point type
*T*:

- S'Exponent denotes a function with the following specification:

```
function S'Exponent (X : T)
return universal_integer
```

- The function yields the normalized exponent of
*X*. See A.5.3.

- S'External_Tag
- For every subtype S of a tagged type
*T*(specific or class-wide):

- S'External_Tag denotes an external string representation for S'Tag; it is of the predefined type String. External_Tag may be specified for a specific tagged type via an attribute_definition_clause; the expression of such a clause shall be static. The default external tag representation is implementation defined. See 3.9.2 and 13.13.2. See 13.3.

- A'First
- For a prefix A that is of an array type (after any implicit dereference), or denotes a constrained array subtype:

- A'First denotes the lower bound of the first index range; its type is the corresponding index type. See 3.6.2.

- S'First
- For every scalar subtype S:

- S'First denotes the lower bound of the range of S. The value of this attribute is of the type of S. See 3.5.

- A'First(N)
- For a prefix A that is of an array type (after any implicit dereference), or denotes a constrained array subtype:

- A'First(N) denotes the lower bound of the N-th index range; its type is the corresponding index type. See 3.6.2.

- R.C'First_Bit
- For a component C of a composite, non-array object R:

- Denotes the offset, from the start of the first of the storage elements occupied by C, of the first bit occupied by C. This offset is measured in bits. The first bit of a storage element is numbered zero. The value of this attribute is of the type
*universal_integer*. See 13.5.2.

- S'Floor
- For every subtype S of a floating point type
*T*:

- S'Floor denotes a function with the following specification:

```
function S'Floor (X : T)
return T
```

- The function yields the value
*Floor*(*X*), i.e., the largest (most positive) integral value less than or equal to*X*. When*X*is zero, the result has the sign of*X*; a zero result otherwise has a positive sign. See A.5.3.

- S'Fore
- For every fixed point subtype S:

- S'Fore yields the minimum number of characters needed before the decimal point for the decimal representation of any value of the subtype S, 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 2.) The value of this attribute is of the type
*universal_integer*. See 3.5.10.

- S'Fraction
- For every subtype S of a floating point type
*T*:

- S'Fraction denotes a function with the following specification:

```
function S'Fraction (X : T)
return T
```

- The function yields the value
*X*·*T'*Machine_Radix^{-k}, where*k*is the normalized exponent of*X*. A zero result, which can only occur when*X*is zero, has the sign of*X*. See A.5.3.

- T'Identity
- For a prefix T that is of a task type (after any implicit dereference):

- Yields a value of the type Task_ID that identifies the task denoted by T. See C.7.1.

- E'Identity
- For a prefix E that denotes an exception:

- E'Identity returns the unique identity of the exception. The type of this attribute is Exception_Id. See 11.4.1.

- S'Image
- For every scalar subtype S:

- S'Image denotes a function with the following specification:

```
function S'Image(Arg : S'Base)
return String
```

- The function returns an image of the value of
*Arg*as a String. See 3.5.

- S'Class'Input
- For every subtype S'Class of a class-wide type
*T'*Class:

- S'Class'Input denotes a function with the following specification:

```
function S'Class'Input( Stream : access Ada.Streams.Root_Stream_Type'Class)
return T'Class
```

- First reads the external tag from
*Stream*and determines the corresponding internal tag (by calling Tags.Internal_Tag(String'Input(*Stream*)) -- see 3.9) and then dispatches to the subprogram denoted by the Input attribute of the specific type identified by the internal tag; returns that result. See 13.13.2.

- S'Input
- For every subtype S of a specific type
*T*:

- S'Input denotes a function with the following specification:

```
function S'Input(
Stream : access Ada.Streams.Root_Stream_Type'Class)
return T
```

- S'Input reads and returns one value from
*Stream*, using any bounds or discriminants written by a corresponding S'Output to determine how much to read. See 13.13.2.

- A'Last
- For a prefix A that is of an array type (after any implicit dereference), or denotes a constrained array subtype:

- A'Last denotes the upper bound of the first index range; its type is the corresponding index type. See 3.6.2.

- S'Last
- For every scalar subtype S:

- S'Last denotes the upper bound of the range of S. The value of this attribute is of the type of S. See 3.5.

- A'Last(N)

- A'Last(N) denotes the upper bound of the N-th index range; its type is the corresponding index type. See 3.6.2.

- R.C'Last_Bit
- For a component C of a composite, non-array object R:

- Denotes the offset, from the start of the first of the storage elements occupied by C, of the last bit occupied by C. This offset is measured in bits. The value of this attribute is of the type
*universal_integer*. See 13.5.2.

- S'Leading_Part
- For every subtype S of a floating point type
*T*:

- S'Leading_Part denotes a function with the following specification:

```
function S'Leading_Part (X : T;
Radix_Digits : universal_integer)
return T
```

- Let
*v*be the value*T'*Machine_Radix^{k-Radix_Digits}, where*k*is the normalized exponent of*X*. The function yields the value

*Floor*(*X*/*v*) ·*v*, when*X*is nonnegative and*Radix_Digits*is positive;

*Ceiling*(*X*/*v*) ·*v*, when*X*is negative and*Radix_Digits*is positive.

- Constraint_Error is raised when
*Radix_Digits*is zero or negative. A zero result, which can only occur when*X*is zero, has the sign of*X*. See A.5.3.

- A'Length

- A'Length denotes the number of values of the first index range (zero for a null range); its type is
*universal_integer*. See 3.6.2.

- A'Length(N)

- A'Length(N) denotes the number of values of the N-th index range (zero for a null range); its type is
*universal_integer*. See 3.6.2.

- S'Machine
- For every subtype S of a floating point type
*T*:

- S'Machine denotes a function with the following specification:

```
function S'Machine (X : T)
return T
```

- If
*X*is a machine number of the type*T*, the function yields*X*; otherwise, it yields the value obtained by rounding or truncating*X*to either one of the adjacent machine numbers of the type*T*. Constraint_Error is raised if rounding or truncating*X*to the precision of the machine numbers results in a value outside the base range of S. A zero result has the sign of*X*when S'Signed_Zeros is True. See A.5.3.

- S'Machine_Emax
- For every subtype S of a floating point type
*T*:

- Yields the largest (most positive) value of
*exponent*such that every value expressible in the canonical form (for the type*T*), having a*mantissa*of*T'*Machine_Mantissa digits, is a machine number (see 3.5.7) of the type*T*. This attribute yields a value of the type*universal_integer*. See A.5.3.

- S'Machine_Emin
- For every subtype S of a floating point type
*T*:

- Yields the smallest (most negative) value of
*exponent*such that every value expressible in the canonical form (for the type*T*), having a*mantissa*of*T'*Machine_Mantissa digits, is a machine number (see 3.5.7) of the type*T*. This attribute yields a value of the type*universal_integer*. See A.5.3.

- S'Machine_Mantissa
- For every subtype S of a floating point type
*T*:

- Yields the largest value of
*p*such that every value expressible in the canonical form (for the type*T*), having a*p*-digit*mantissa*and an*exponent*between*T***Machine_Emin and****T**Machine_Emax, is a machine number (see 3.5.7) of the type*T*. This attribute yields a value of the type*universal_integer*. See A.5.3.

- S'Machine_Overflows
- For every subtype S of a fixed point type
*T*:

- Yields the value True if overflow and divide-by-zero are detected and reported by raising Constraint_Error for every predefined operation that yields a result of the type
*T*; yields the value False otherwise. The value of this attribute is of the predefined type Boolean. See A.5.4.

- S'Machine_Overflows
- For every subtype S of a floating point type
*T*:

- Yields the value True if overflow and divide-by-zero are detected and reported by raising Constraint_Error for every predefined operation that yields a result of the type
*T*; yields the value False otherwise. The value of this attribute is of the predefined type Boolean. See A.5.3.

- S'Machine_Radix
- For every subtype S of a fixed point type
*T*:

- Yields the radix of the hardware representation of the type
*T*. The value of this attribute is of the type*universal_integer*. See A.5.4.

- S'Machine_Radix
- For every subtype S of a floating point type
*T*:

- Yields the radix of the hardware representation of the type
*T*. The value of this attribute is of the type*universal_integer*. See A.5.3.

- S'Machine_Rounds
- For every subtype S of a fixed point type
*T*:

- Yields the value True if rounding is performed on inexact results of every predefined operation that yields a result of the type
*T*; yields the value False otherwise. The value of this attribute is of the predefined type Boolean. See A.5.4.

- S'Machine_Rounds
- For every subtype S of a floating point type
*T*:

- Yields the value True if rounding is performed on inexact results of every predefined operation that yields a result of the type
*T*; yields the value False otherwise. The value of this attribute is of the predefined type Boolean. See A.5.3.

- S'Max
- For every scalar subtype S:

- S'Max denotes a function with the following specification:

```
function S'Max(Left, Right : S'Base) return S'Base
```

- The function returns the greater of the values of the two parameters. See 3.5.

- S'Max_Size_In_Storage_Elements
- For every subtype S:

- Denotes the maximum value for Size_In_Storage_Elements that will be requested via Allocate for an access type whose designated subtype is S. The value of this attribute is of type
*universal_integer*. See 13.11.1.

- S'Min
- For every scalar subtype S:

- S'Min denotes a function with the following specification:

```
function S'Min(Left, Right : S'Base) return S'Base
```

- The function returns the lesser of the values of the two parameters. See 3.5.

- S'Model
- For every subtype S of a floating point type
*T*:

- S'Model denotes a function with the following specification:

```
function S'Model (X : T) return T
```

- If the Numerics Annex is not supported, the meaning of this attribute is implementation defined; see G.2.2 for the definition that applies to implementations supporting the Numerics Annex. See A.5.3.

- S'Model_Emin
- For every subtype S of a floating point type
*T*:

- If the Numerics Annex is not supported, this attribute yields an implementation defined value that is greater than or equal to the value of
*T'*Machine_Emin. See G.2.2 for further requirements that apply to implementations supporting the Numerics Annex. The value of this attribute is of the type*universal_integer*. See A.5.3.

- S'Model_Epsilon
- For every subtype S of a floating point type
*T*:

- Yields the value
*T***Machine_Radix**^{1 - }**T**Model_Mantissa. The value of this attribute is of the type*universal_real*. See A.5.3.

- S'Model_Mantissa
- For every subtype S of a floating point type
*T*:

- If the Numerics Annex is not supported, this attribute yields an implementation defined value that is greater than or equal to
*Ceiling*(*d*· log(10) / log(*T***Machine_Radix)) + 1, where****d**Machine_Mantissa. See G.2.2 for further requirements that apply to implementations supporting the Numerics Annex. The value of this attribute is of the type*is the requested decimal precision of*T*, and less than or equal to the value of*T*universal_integer*. See A.5.3.

- S'Model_Small
- For every subtype S of a floating point type
*T*:

- Yields the value
*T***Machine_Radix**^{}**T**Model_Emin - 1. The value of this attribute is of the type*universal_real*. See A.5.3.

- S'Modulus
- For every modular subtype S:

- S'Modulus yields the modulus of the type of S, as a value of the type
*universal_integer*. See 3.5.4.

- S'Class'Output
- For every subtype S'Class of a class-wide type
*T'*Class:

- S'Class'Output denotes a procedure with the following specification:

```
procedure S'Class'Output(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T'Class)
```

- First writes the external tag of
*Item*to*Stream*(by calling String'Output(Tags.External_Tag(*Item'*Tag) -- see 3.9) and then dispatches to the subprogram denoted by the Output attribute of the specific type identified by the tag. See 13.13.2.

- S'Output
- For every subtype S of a specific type
*T*:

- S'Output denotes a procedure with the following specification:

```
procedure S'Output(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T)
```

- S'Output writes the value of
*Item*to*Stream*, including any bounds or discriminants. See 13.13.2.

- D'Partition_ID
- For a prefix D that denotes a library-level declaration, excepting a declaration of or within a declared-pure library unit:

- Denotes a value of the type
*universal_integer*that identifies the partition in which D was elaborated. If D denotes the declaration of a remote call interface library unit (see E.2.3) the given partition is the one where the body of D was elaborated. See E.1.

- S'Pos
- For every discrete subtype S:

- S'Pos denotes a function with the following specification:

```
function S'Pos(Arg : S'Base)
return universal_integer
```

- This function returns the position number of the value of
*Arg*, as a value of type*universal_integer*. See 3.5.5.

- R.C'Position
- For a component C of a composite, non-array object R:

- Denotes the same value as R.C'Address - R'Address. The value of this attribute is of the type
*universal_integer*. See 13.5.2.

- S'Pred
- For every scalar subtype S:

- S'Pred denotes a function with the following specification:

```
function S'Pred(Arg : S'Base)
return S'Base
```

- For an enumeration type, the function returns the value whose position number is one less than that of the value of
*Arg*; Constraint_Error is raised if there is no such value of the type. For an integer type, the function returns the result of subtracting one from the value of*Arg*. For a fixed point type, the function returns the result of subtracting*small*from the value of*Arg*. For a floating point type, the function returns the machine number (as defined in 3.5.7) immediately below the value of*Arg*; Constraint_Error is raised if there is no such machine number. See 3.5.

- A'Range

- A'Range is equivalent to the range A'First .. A'Last, except that the prefix A is only evaluated once. See 3.6.2.

- S'Range
- For every scalar subtype S:

- S'Range is equivalent to the range S'First .. S'Last. See 3.5.

- A'Range(N)

- A'Range(N) is equivalent to the range A'First(N) .. A'Last(N), except that the prefix A is only evaluated once. See 3.6.2.

- S'Class'Read
- For every subtype S'Class of a class-wide type
*T'*Class:

- S'Class'Read denotes a procedure with the following specification:

```
procedure S'Class'Read(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : out T'Class)
```

- Dispatches to the subprogram denoted by the Read attribute of the specific type identified by the tag of Item. See 13.13.2.

- S'Read
- For every subtype S of a specific type
*T*:

- S'Read denotes a procedure with the following specification:

```
procedure S'Read(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : out T)
```

- S'Read reads the value of
*Item*from*Stream*. See 13.13.2.

- S'Remainder
- For every subtype S of a floating point type
*T*:

- S'Remainder denotes a function with the following specification:

```
function S'Remainder (X, Y : T)
return T
```

- For nonzero
*Y*, let*v*be the value*X*-*n*·*Y*, where*n*is the integer nearest to the exact value of*X*/*Y*; if |*n*-*X*/*Y*| = 1/2, then*n*is chosen to be even. If*v*is a machine number of the type*T*, the function yields*v*; otherwise, it yields zero. Constraint_Error is raised if*Y*is zero. A zero result has the sign of*X*when S'Signed_Zeros is True. See A.5.3.

- S'Round
- For every decimal fixed point subtype S:

- S'Round denotes a function with the following specification:

```
function S'Round(X : universal_real)
return S'Base
```

- The function returns the value obtained by rounding X (away from 0, if X is midway between two values of the type of S). See 3.5.10.

- S'Rounding
- For every subtype S of a floating point type
*T*:

- S'Rounding denotes a function with the following specification:

```
function S'Rounding (X : T)
return T
```

- The function yields the integral value nearest to
*X*, rounding away from zero if*X*lies exactly halfway between two integers. A zero result has the sign of*X*when S'Signed_Zeros is True. See A.5.3.

- S'Safe_First
- For every subtype S of a floating point type
*T*:

- Yields the lower bound of the safe range (see 3.5.7) of the type
*T*. If the Numerics Annex is not supported, the value of this attribute is implementation defined; see G.2.2 for the definition that applies to implementations supporting the Numerics Annex. The value of this attribute is of the type*universal_real*. See A.5.3.

- S'Safe_Last
- For every subtype S of a floating point type
*T*:

- Yields the upper bound of the safe range (see 3.5.7) of the type
*T*. If the Numerics Annex is not supported, the value of this attribute is implementation defined; see G.2.2 for the definition that applies to implementations supporting the Numerics Annex. The value of this attribute is of the type*universal_real*. See A.5.3.

- S'Scale
- For every decimal fixed point subtype S:

- S'Scale denotes the
*scale*of the subtype S, defined as the value N such that S'Delta = 10.0**(-N). The scale indicates the position of the point relative to the rightmost significant digits of values of subtype S. The value of this attribute is of the type*universal_integer*. See 3.5.10.

- S'Scaling
- For every subtype S of a floating point type
*T*:

- S'Scaling denotes a function with the following specification:

```
function S'Scaling (X : T;
Adjustment : universal_integer)
return T
```

- Let
*v*be the value*X*·*T***Machine_Radix**^{}**Adjustment**Model_Small, the function yields*. If*v*is a machine number of the type*T*, or if |*v*| >=*T*v*; otherwise, it yields either one of the machine numbers of the type*T*adjacent to*v*. Constraint_Error is optionally raised if*v*is outside the base range of S. A zero result has the sign of*X*when S'Signed_Zeros is True. See A.5.3.

- S'Signed_Zeros
- For every subtype S of a floating point type
*T*:

- Yields the value True if the hardware representation for the type
*T*has the capability of representing both positively and negatively signed zeros, these being generated and used by the predefined operations of the type*T*as specified in IEC 559:1989; yields the value False otherwise. The value of this attribute is of the predefined type Boolean. See A.5.3.

- S'Size
- For every subtype S:

- If S is definite, denotes the size (in bits) that the implementation would choose for the following objects of subtype S:

- A record component of subtype S when the record type is packed.

- The formal parameter of an instance of Unchecked_Conversion that converts from subtype S to some other subtype.

- If S is indefinite, the meaning is implementation defined. The value of this attribute is of the type
*universal_integer*. See 13.3.

- X'Size
- For a prefix X that denotes an object:

- Denotes the size in bits of the representation of the object. The value of this attribute is of the type
*universal_integer*. See 13.3.

- S'Small
- For every fixed point subtype S:

- S'Small denotes the
*small*of the type of S. The value of this attribute is of the type*universal_real*. See 3.5.10.

- S'Storage_Pool
- For every access subtype S:

- Denotes the storage pool of the type of S. The type of this attribute is Root_Storage_Pool'Class. See 13.11.

- S'Storage_Size
- For every access subtype S:

- Yields the result of calling Storage_Size(S'Storage_Pool), which is intended to be a measure of the number of storage elements reserved for the pool. The type of this attribute is
*universal_integer*. See 13.11.

- T'Storage_Size
- For a prefix T that denotes a task object (after any implicit dereference):

- Denotes the number of storage elements reserved for the task. The value of this attribute is of the type
*universal_integer*. The Storage_Size includes the size of the task's stack, if any. The language does not specify whether or not it includes other storage associated with the task (such as the*task control block*used by some implementations.) See 13.3.

- S'Succ
- For every scalar subtype S:

- S'Succ denotes a function with the following specification:

```
function S'Succ(Arg : S'Base)
return S'Base
```

- For an enumeration type, the function returns the value whose position number is one more than that of the value of
*Arg*; Constraint_Error is raised if there is no such value of the type. For an integer type, the function returns the result of adding one to the value of*Arg*. For a fixed point type, the function returns the result of adding*small*to the value of*Arg*. For a floating point type, the function returns the machine number (as defined in 3.5.7) immediately above the value of*Arg*; Constraint_Error is raised if there is no such machine number. See 3.5.

- X'Tag
- For a prefix X that is of a class-wide tagged type (after any implicit dereference):

- X'Tag denotes the tag of X. The value of this attribute is of type Tag. See 3.9.

- S'Tag
- For every subtype S of a tagged type
*T*(specific or class-wide):

- S'Tag denotes the tag of the type
*T*(or if*T*is class-wide, the tag of the root type of the corresponding class). The value of this attribute is of type Tag. See 3.9.

- T'Terminated
- For a prefix T that is of a task type (after any implicit dereference):

- Yields the value True if the task denoted by T is terminated, and False otherwise. The value of this attribute is of the predefined type Boolean. See 9.9.

- S'Truncation
- For every subtype S of a floating point type
*T*:

- S'Truncation denotes a function with the following specification:

```
function S'Truncation (X : T)
return T
```

- The function yields the value
*Ceiling*(*X*) when*X*is negative, and*Floor*(*X*) otherwise. A zero result has the sign of*X*when S'Signed_Zeros is True. See A.5.3.

- S'Unbiased_Rounding
- For every subtype S of a floating point type
*T*:

- S'Unbiased_Rounding denotes a function with the following specification:

```
function S'Unbiased_Rounding (X : T)
return T
```

- The function yields the integral value nearest to
*X*, rounding toward the even integer if*X*lies exactly halfway between two integers. A zero result has the sign of*X*when S'Signed_Zeros is True. See A.5.3.

- X'Unchecked_Access
- For a prefix X that denotes an aliased view of an object:

- All rules and semantics that apply to X'Access (see 3.10.2) apply also to X'Unchecked_Access, except that, for the purposes of accessibility rules and checks, it is as if X were declared immediately within a library package. See 13.10.

- S'Val
- For every discrete subtype S:

- S'Val denotes a function with the following specification:

```
function S'Val(Arg : universal_integer)
return S'Base
```

- This function returns a value of the type of S whose position number equals the value of
*Arg*. See 3.5.5.

- X'Valid
- For a prefix X that denotes a scalar object (after any implicit dereference):

- Yields True if and only if the object denoted by X is normal and has a valid representation. The value of this attribute is of the predefined type Boolean. See 13.9.2.

- S'Value
- For every scalar subtype S:

- S'Value denotes a function with the following specification:

```
function S'Value(Arg : String)
return S'Base
```

- This function returns a value given an image of the value as a String, ignoring any leading or trailing spaces. See 3.5.

- P'Version
- For a prefix P that statically denotes a program unit:

- Yields a value of the predefined type String that identifies the version of the compilation unit that contains the declaration of the program unit. See E.3.

- S'Wide_Image
- For every scalar subtype S:

- S'Wide_Image denotes a function with the following specification:

```
function S'Wide_Image(Arg : S'Base)
return Wide_String
```

- The function returns an
*image*of the value of*Arg*, that is, a sequence of characters representing the value in display form. See 3.5.

- S'Wide_Value
- For every scalar subtype S:

- S'Wide_Value denotes a function with the following specification:

```
function S'Wide_Value(Arg : Wide_String)
return S'Base
```

- This function returns a value given an image of the value as a Wide_String, ignoring any leading or trailing spaces. See 3.5.

- S'Wide_Width
- For every scalar subtype S:

- S'Wide_Width denotes the maximum length of a Wide_String returned by S'Wide_Image over all values of the subtype S. It denotes zero for a subtype that has a null range. Its type is
*universal_integer*. See 3.5.

- S'Width
- For every scalar subtype S:

- S'Width denotes the maximum length of a String returned by S'Image over all values of the subtype S. It denotes zero for a subtype that has a null range. Its type is
*universal_integer*. See 3.5.

- S'Class'Write
- For every subtype S'Class of a class-wide type
*T'*Class:

- S'Class'Write denotes a procedure with the following specification:

```
procedure S'Class'Write(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T'Class)
```

- Dispatches to the subprogram denoted by the Write attribute of the specific type identified by the tag of Item. See 13.13.2.

- S'Write
- For every subtype S of a specific type
*T*:

- S'Write denotes a procedure with the following specification:

```
procedure S'Write(
Stream : access Ada.Streams.Root_Stream_Type'Class;
Item : in T)
```

- S'Write writes the value of
*Item*to*Stream*. See 13.13.2.

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Copyright © 2000 The MITRE Corporation, Inc.
Ada Reference Manual