13.14 Freezing Rules
1
This clause defines a place in the program text where
each declared entity becomes “frozen.” A use of an entity,
such as a reference to it by name, or (for a type) an expression of the
type, causes freezing of the entity in some contexts, as described below.
The Legality Rules forbid certain kinds of uses of an entity in the region
of text where it is frozen.
2
The
freezing
of an entity occurs at one or more places (
freezing points) in
the program text where the representation for the entity has to be fully
determined. Each entity is frozen from its first freezing point to the
end of the program text (given the ordering of compilation units defined
in
10.1.4).
3/1
The end of a
declarative_part,
protected_body, or a declaration of a library
package or generic library package, causes
freezing of each entity
declared within it, except for incomplete types.
A
noninstance body other than a renames-as-body causes freezing of each
entity declared before it within the same
declarative_part.
4/1
A
construct that (explicitly or implicitly) references an entity can cause
the
freezing of the entity, as defined by subsequent paragraphs.
At the place where a construct causes freezing, each
name,
expression,
implicit_dereference, or
range
within the construct causes freezing:
5
- The
occurrence of a generic_instantiation causes
freezing; also, if a parameter of the instantiation is defaulted, the
default_expression or default_name
for that parameter causes freezing.
6
- The
occurrence of an object_declaration that has
no corresponding completion causes freezing.
7
- The declaration
of a record extension causes freezing of the parent subtype.
7.1/2
- The declaration of a record extension,
interface type, task unit, or protected unit causes freezing of any progenitor
types specified in the declaration.
8/1
A static expression causes freezing
where it occurs.
An object name or nonstatic expression
causes freezing where it occurs, unless the name or expression is part
of a
default_expression, a
default_name,
or a per-object expression of a component's
constraint,
in which case, the freezing occurs later as part of another construct.
8.1/1
An implicit call freezes the
same entities that would be frozen by an explicit call. This is true
even if the implicit call is removed via implementation permissions.
8.2/1
If an expression is implicitly
converted to a type or subtype
T, then at the place where the
expression causes freezing,
T is frozen.
9
The following rules
define which entities are frozen at the place where a construct causes
freezing:
10
- At
the place where an expression causes freezing, the type of the expression
is frozen, unless the expression is an enumeration literal used as a
discrete_choice of the array_aggregate
of an enumeration_representation_clause.
11
- At
the place where a name causes freezing, the
entity denoted by the name is frozen, unless
the name is a prefix
of an expanded name; at the place where an object
name causes freezing, the nominal subtype
associated with the name is frozen.
11.1/1
- At
the place where an implicit_dereference causes
freezing, the nominal subtype associated with the implicit_dereference
is frozen.
12
- At
the place where a range causes freezing, the
type of the range is frozen.
13
- At
the place where an allocator causes freezing,
the designated subtype of its type is frozen. If the type of the allocator
is a derived type, then all ancestor types are also frozen.
14
- At
the place where a callable entity is frozen, each subtype of its profile
is frozen. If the callable entity is a member of an entry family, the
index subtype of the family is frozen. At the place
where a function call causes freezing, if a parameter of the call is
defaulted, the default_expression for that
parameter causes freezing.
15
- At
the place where a subtype is frozen, its type is frozen. At
the place where a type is frozen, any expressions or names
within the full type definition cause freezing; the first subtype, and
any component subtypes, index subtypes, and parent subtype of the type
are frozen as well. For a specific
tagged type, the corresponding class-wide type is frozen as well. For
a class-wide type, the corresponding specific type is frozen as well.
15.1/2
- At the
place where a specific tagged type is frozen, the primitive subprograms
of the type are frozen.
Legality Rules
16
The explicit declaration
of a primitive subprogram of a tagged type shall occur before the type
is frozen (see
3.9.2).
17
A type shall be completely
defined before it is frozen (see
3.11.1
and
7.3).
18
The completion of a
deferred constant declaration shall occur before the constant is frozen
(see
7.4).
19/1
An operational or
representation item that directly specifies an aspect of an entity shall
appear before the entity is frozen (see
13.1).
Dynamic Semantics
20/2
The tag (see
3.9) of a
tagged type T is created at the point where T is frozen.
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