4.1.1 Indexed Components
[An
indexed_component
denotes either a component of an array or an entry in a family of entries.
{array indexing: See indexed_component}
]
Syntax
Name Resolution Rules
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).
{expected type (indexed_component
expression) [partial]} The expected type
for each
expression
is the corresponding index type.
Static Semantics
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.
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
{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
Examples of indexed
components:
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)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