4.1.1 Indexed Components
1
[An
indexed_component
denotes either a component of an array or an entry in a family of entries.
{array indexing: See indexed_component}
]
Syntax
2
indexed_component ::= prefix(
expression {,
expression})
Name Resolution Rules
3
The prefix of an indexed_component
with a given number of expressions shall resolve
to denote an array (after any implicit dereference) with the corresponding
number of index positions, or shall resolve to denote an entry family
of a task or protected object (in which case there shall be only one
expression).
4
{expected type (indexed_component
expression) [partial]} The expected type
for each
expression is the corresponding index
type.
Static Semantics
5
When the
prefix denotes
an array, the
indexed_component denotes the
component of the array with the specified index value(s).
{nominal
subtype (associated with an indexed_component) [partial]}
The nominal subtype of the
indexed_component
is the component subtype of the array type.
5.a/2
This paragraph
was deleted.Ramification: {
AI95-00363-01}
In the case of an array whose components are aliased,
and of an unconstrained discriminated subtype, the components are constrained
even though their nominal subtype is unconstrained. (This is because
all aliased discriminated objects are constrained. See 3.10.2.)
In all other cases, an array component is constrained if and only if
its nominal subtype is constrained.
6
When the prefix denotes
an entry family, the indexed_component denotes
the individual entry of the entry family with the specified index value.
Dynamic Semantics
7
{evaluation (indexed_component)
[partial]} For the evaluation of an
indexed_component,
the
prefix and the
expressions
are evaluated in an arbitrary order. The value of each
expression
is converted to the corresponding index type.
{implicit
subtype conversion (array index) [partial]} {Index_Check
[partial]} {check,
language-defined (Index_Check)} A check
is made that each index value belongs to the corresponding index range
of the array or entry family denoted by the
prefix.
{Constraint_Error (raised by failure
of run-time check)} Constraint_Error is
raised if this check fails.
Examples
8
Examples of indexed
components:
9
My_Schedule(Sat) --
a component of a one-dimensional array (see 3.6.1)
Page(10) --
a component of a one-dimensional array (see 3.6)
Board(M, J + 1) --
a component of a two-dimensional array (see 3.6.1)
Page(10)(20) --
a component of a component (see 3.6)
Request(Medium) --
an entry in a family of entries (see 9.1)
Next_Frame(L)(M, N) --
a component of a function call (see 6.1)10
1 Notes on the examples: Distinct
notations are used for components of multidimensional arrays (such as
Board) and arrays of arrays (such as Page). The components of an array
of arrays are arrays and can therefore be indexed. Thus Page(10)(20)
denotes the 20th component of Page(10). In the last example Next_Frame(L)
is a function call returning an access value that designates a two-dimensional
array.
Sponsored by Ada-Europe