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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
2
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.
6
The type of the slice
is that of the prefix. Its bounds
are those defined by the discrete_range.
Dynamic Semantics
7
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.
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.
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
10
Examples of
slices:
11
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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