4.1.2 Slices
1
[
{array slice}
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
{expected type (slice
discrete_range) [partial]} 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
{evaluation (slice)
[partial]} For the evaluation of a
slice,
the
prefix and the
discrete_range
are evaluated in an arbitrary order.
{Index_Check
[partial]} {check,
language-defined (Index_Check)} {null
slice} 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 (raised by failure
of run-time check)} 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.
8.a
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
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
Sponsored by Ada-Europe