12.5.3 Formal Array Types
1/2
{
AI95-00442-01}
[The
category class
determined for a formal array type is the
category class
of all array types.]
1.a/2
Proof: {
AI95-00442-01}
This rule follows from the rule in 12.5
that says that the category is determined by the one given in the name
of the syntax production. The effect of the rule is repeated here to
give a capsule summary of what this subclause is about.
Syntax
2
formal_array_type_definition ::= array_type_definition
Legality Rules
3
The only form of discrete_subtype_definition
that is allowed within the declaration of a generic formal (constrained)
array subtype is a subtype_mark.
3.a
Reason: The reason is the same as for
forbidding
constraints in
subtype_indications
(see
12.1).
4
For a formal array
subtype, the actual subtype shall satisfy the following conditions:
5
- The formal array type and the actual
array type shall have the same dimensionality; the formal subtype and
the actual subtype shall be either both constrained or both unconstrained.
6
- For each index position, the index
types shall be the same, and the index subtypes (if unconstrained), or
the index ranges (if constrained), shall statically match (see 4.9.1).
{statically matching (required) [partial]}
7
- The component subtypes of the formal
and actual array types shall statically match. {statically
matching (required) [partial]}
8
- If the formal type has aliased components,
then so shall the actual.
8.a
Ramification: On the other hand, if the
formal's components are not aliased, then the actual's components can
be either aliased or not.
Examples
9
Example of formal
array types:
10
-- given the generic package
11
generic
type Item is private;
type Index is (<>);
type Vector is array (Index range <>) of Item;
type Table is array (Index) of Item;
package P is
...
end P;
12
-- and the types
13
type Mix is array (Color range <>) of Boolean;
type Option is array (Color) of Boolean;
14
-- then Mix can match Vector and Option can match Table
15
package R is new P(Item => Boolean, Index => Color,
Vector => Mix, Table => Option);
16
-- Note that Mix cannot match Table and Option cannot match Vector
Incompatibilities With Ada 83
16.a
{
incompatibilities with Ada 83}
The
check for matching of component subtypes and index subtypes or index
ranges is changed from a run-time check to a compile-time check. The
Ada 83 rule that “If the component type is not a scalar type, then
the component subtypes shall be either both constrained or both unconstrained”
is removed, since it is subsumed by static matching. Likewise, the rules
requiring that component types be the same is subsumed.
Wording Changes from Ada 95
16.b/2
{
AI95-00442-01}
We change to “determines a category”
as that is the new terminology (it avoids confusion, since not all interesting
properties form a class).
Sponsored by Ada-Europe