- Unchecked storage deallocation of an object designated by a value of an
access type is achieved by a call to an instance of the generic procedure
- The following language-defined generic library procedure exists:
type Object(<>) is limited private;
type Name is access Object;
procedure Ada.Unchecked_Deallocation(X : in out Name);
pragma Convention(Intrinsic, Ada.Unchecked_Deallocation);
- Given an instance of Unchecked_Deallocation declared as follows:
procedure Free is
- Procedure Free has the following effect:
- After executing Free(X), the value of X is null.
- Free(X), when X is already equal to null, has no effect.
- Free(X), when X is not equal to null first performs finalization, as
described in 7.6. It then deallocates the storage
occupied by the object designated by X. If the storage pool is a user-defined
object, then the storage is deallocated by calling Deallocate, passing
access_to_variable_subtype_name'Storage_Pool as the Pool parameter. Storage_Address
is the value returned in the Storage_Address parameter of the corresponding
Allocate call. Size_In_Storage_Elements and Alignment are the same values
passed to the corresponding Allocate call. There is one exception: if
the object being freed contains tasks, the object might not be deallocated.
- After Free(X), the object designated by X, and any subcomponents
thereof, no longer exist; their storage can be reused for other purposes.
Bounded (Run-Time) Errors
- It is a bounded error to free a discriminated, unterminated task object.
The possible consequences are:
- Program_Error or Tasking_Error is raised at the point of the
- Program_Error or Tasking_Error is raised in the task the next
time it references any of the discriminants.
- In the first two cases, the storage for the discriminants (and for any
enclosing object if it is designated by an access discriminant of the task)
is not reclaimed prior to task termination.
- Evaluating a name that denotes a nonexistent object is erroneous. The
execution of a call to an instance of Unchecked_Deallocation is erroneous if
the object was created other than by an allocator for an access type whose
pool is Name'Storage_Pool.
- For a standard storage pool, Free should actually reclaim the storage.
(26) The rules here that refer to Free apply to any instance of
(27) Unchecked_Deallocation cannot be instantiated for an access-to- constant
type. This is implied by the rules of 12.5.4.
-- Email comments, additions, corrections, gripes, kudos, etc. to:
Magnus Kempe -- Magnus.Kempe@di.epfl.ch
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