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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.
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.
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).
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