7.3.3 Default Initial Conditions
This aspect shall be specified by an
expression,
called a
default initial condition expression. Default_Initial_Condition
may be specified on a
private_type_declaration,
a
private_extension_declaration,
a
formal_private_type_definition,
or a
formal_derived_type_definition.
Aspect Description for Default_Initial_Condition:
A condition that must hold true after the default initialization
of an object.
Glossary entry: A property that holds
for every default-initialized object of a given type.
Name Resolution Rules
{
AI12-0265-1}
The expected type for a default initial condition expression is any boolean
type.
Legality Rules
{
AI12-0265-1}
The Default_Initial_Condition aspect shall not be specified for a type
whose partial view has unknown discriminants[, whether explicitly declared
or inherited].
Static Semantics
{
AI12-0265-1}
If the Default_Initial_Condition aspect is specified for a type T, then
the default initial condition expression applies to T and to all descendants
of T.
Dynamic Semantics
{
AI12-0265-1}
If one or more default initial condition expressions apply to a type
T, then a default initial condition check is performed after successful
initialization of an object of type T by default (see
3.3.1).
In the case of a controlled type, the check is performed after the call
to the type's Initialize procedure (see
7.6).
{
AI12-0265-1}
If performing checks is required by the Default_Initial_Condition assertion
policy (see
11.4.2) in effect at the point
of the corresponding
aspect_specification
applicable to a given type, then the respective default initial condition
expression is considered enabled.
{
AI12-0265-1}
The default initial condition check consists of the evaluation of each
enabled default initial condition expression that applies to T. These
evaluations, if there are more than one, are performed in an arbitrary
order. If any of these evaluate to False, Assertions.Assertion_Error
is raised at the point of the object initialization.
{
AI12-0272-1}
[For a generic formal type T, default initial condition checks performed
are as determined by the actual type, along with any default initial
condition of the formal type itself.]
Proof: This follows from the general
dynamic semantics rules given above, but we mention it explicitly so
that there can be no doubt that it is intended.
Implementation Permissions
{
AI12-0332-1}
Implementations may extend the syntax or semantics of the Default_Initial_Condition
aspect in an implementation-defined manner.
Implementation defined: Any extensions
of the Default_Initial_Condition aspect.
Reason: This is intended to allow preexisting
usages from SPARK 2014 to remain acceptable in conforming implementations,
as well as to provide future flexibility. Note the word “extend”
in this permission; we expect that any aspect usage that conforms with
the (other) rules of this clause will be accepted by any Ada implementation,
regardless of any implementation-defined extensions.
14 {
AI12-0312-1}
For an example of the use of this aspect, see the Vector container definition
in
A.18.2.
Extensions to Ada 2012
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe