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4.1.2 Slices

1
[ A slice denotes a one-dimensional array formed by a sequence of consecutive components of a one-dimensional array. A slice of a variable is a variable; a slice of a constant is a constant;] a slice of a value is a value. 

Syntax

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slice ::= prefix(discrete_range)

Name Resolution Rules

3
The prefix of a slice shall resolve to denote a one-dimensional array (after any implicit dereference).
4
The expected type for the discrete_range of a slice is the index type of the array type. 

Static Semantics

5
A slice denotes a one-dimensional array formed by the sequence of consecutive components of the array denoted by the prefix, corresponding to the range of values of the index given by the discrete_range.
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The type of the slice is that of the prefix. Its bounds are those defined by the discrete_range.

Dynamic Semantics

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For the evaluation of a slice, the prefix and the discrete_range are evaluated in an arbitrary order. If the slice is not a null slice (a slice where the discrete_range is a null range), then a check is made that the bounds of the discrete_range belong to the index range of the array denoted by the prefix. Constraint_Error is raised if this check fails.
NOTES
8
2  A slice is not permitted as the prefix of an Access attribute_reference, even if the components or the array as a whole are aliased. See 3.10.2.
8.a
Proof: Slices are not aliased, by 3.10, “Access Types”. 
8.b
Reason: This is to ease implementation of general-access-to-array. If slices were aliased, implementations would need to store array dope with the access values, which is not always desirable given access-to-incomplete types completed in a package body.
9
3  For a one-dimensional array A, the slice A(N .. N) denotes an array that has only one component; its type is the type of A. On the other hand, A(N) denotes a component of the array A and has the corresponding component type. 

Examples

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Examples of slices:
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  Stars(1 .. 15)        --  a slice of 15 characters          (see 3.6.3)
  Page(10 .. 10 + Size) --  a slice of 1 + Size components    (see 3.6)
  Page(L)(A .. B)       --  a slice of the array Page(L)      (see 3.6)
  Stars(1 .. 0)         --  a null slice                      (see 3.6.3)
  My_Schedule(Weekday)  --  bounds given by subtype           (see 3.6.1 and 3.5.1)
  Stars(5 .. 15)(K)     --  same as Stars(K)                  (see 3.6.3)
                        --  provided that K is in 5 .. 15
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