A.18.25 The Generic Package Containers.Bounded_Multiway_Trees
The language-defined generic package Containers.Bounded_Multiway_Trees
provides a private type Tree and a set of operations. It provides the
same operations as the package Containers.Multiway_Trees (see
A.18.10),
with the difference that the maximum storage is bounded.
Static Semantics
The declaration of
the generic library package Containers.Bounded_Multiway_Trees has the
same contents and semantics as Containers.Multiway_Trees except:
The aspect Preelaborate is replaced with aspect
Pure. Aspect Global is deleted.
The type Tree is
declared with a discriminant that specifies the capacity (maximum number
of elements) as follows:
type Tree (Capacity : Count_Type) is tagged private...
Preelaborable_Initialization =>
Element_Type'Preelaborable_Initialization
The type Tree needs finalization if and only if
type Element_Type needs finalization.
The function Empty
is replaced by:
function Empty (Capacity : Count_Type := implementation-defined)
return Tree
with Post =>
Empty'Result.Capacity = Capacity and then
not Tampering_With_Elements_Prohibited (Empty'Result) and then
not Tampering_With_Cursors_Prohibited (Empty'Result) and then
Node_Count (Empty'Result) = 1;
For procedures Insert_Child, Prepend_Child, and
Append_Child, the initial subexpression of the precondition is replaced
with:
with Pre => (not Tampering_With_Cursors_Prohibited (Container)
or else raise Program_Error) and then
(Node_Count (Container) - 1 <= Container.Capacity - Count
or else raise Capacity_Error)
In procedure Assign, the precondition is altered
to:
Pre => (not Tampering_With_Cursors_Prohibited (Target)
or else raise Program_Error) and then
(Node_Count (Source) - 1 <= Target.Capacity
or else raise Capacity_Error),
Function Copy is
declared as follows:
function Copy (Source : Tree; Capacity : Count_Type := 0)
return Tree
with Pre => Capacity = 0 or else Capacity >= Node_Count (Source) - 1
or else raise Capacity_Error,
Post =>
Node_Count (Copy'Result) = Node_Count (Source) and then
not Tampering_With_Elements_Prohibited (Copy'Result) and then
not Tampering_With_Cursors_Prohibited (Copy'Result) and then
Copy'Result.Capacity = (if Capacity = 0 then
Node_Count (Source) - 1 else Capacity);
Returns a list whose elements have the same values
as the elements of Source.
In the four-parameter
procedure Copy_Subtree, the last or else of the precondition is
replaced by:
(not Is_Root (Source)
or else raise Constraint_Error) and then
(Node_Count (Target) - 1 + Subtree_Node_Count (Source) <=
Target.Capacity
or else raise Capacity_Error),
In the five-parameter
procedure Copy_Subtree, the last or else of the precondition is
replaced by:
(not Is_Root (Source, Subtree)
or else raise Constraint_Error) and then
(Node_Count (Target) - 1 +
Subtree_Node_Count (Source, Subtree) <= Target.Capacity
or else raise Capacity_Error),
In Copy_Local_Subtree,
the last or else of the precondition is replaced by:
(not Is_Root (Source, Subtree)
or else raise Constraint_Error) and then
(Node_Count (Target) - 1 +
Subtree_Node_Count (Target, Source) <= Target.Capacity
or else raise Capacity_Error),
In the five-parameter procedure Splice_Subtree,
the penultimate or else of the precondition is replaced by:
(Has_Element (Source, Position)
or else raise Program_Error) and then
(Target'Has_Same_Storage (Source) or else
Node_Count (Target) - 1 +
Subtree_Node_Count (Source, Position) <= Target.Capacity
or else raise Capacity_Error) and then
In the five-parameter procedure Splice_Children,
the penultimate elsif of the precondition is replaced by:
(Before = No_Element or else
Parent (Target, Before) /= Target_Parent
or else raise Constraint_Error) and then
(Target'Has_Same_Storage (Source) or else
Node_Count (Target) - 1 +
Child_Count (Source, Source_Parent) <= Target.Capacity
or else raise Capacity_Error) and then
Bounded (Run-Time) Errors
It is a bounded error to assign
from a bounded tree object while tampering with elements or cursors of
that object is prohibited. Either Program_Error is raised by the assignment,
execution proceeds with the target object prohibiting tampering with
elements or cursors, or execution proceeds normally.
Erroneous Execution
When a bounded tree object
T is finalized,
if tampering with cursors is prohibited for
T other than due to
an assignment from another tree, then execution is erroneous.
Implementation Requirements
For each instance of
Containers.Multiway_Trees and each instance of Containers.Bounded_Multiway_Trees,
if the two instances meet the following conditions, then the output generated
by the Tree'Output or Tree'Write subprograms of either instance shall
be readable by the Tree'Input or Tree'Read of the other instance, respectively:
the Element_Type parameters of the two instances
are statically matching subtypes of the same type; and
the output generated by Element_Type'Output or
Element_Type'Write is readable by Element_Type'Input or Element_Type'Read,
respectively (where Element_Type denotes the type of the two actual Element_Type
parameters).
Implementation Advice
Bounded tree objects should be implemented without
implicit pointers or dynamic allocation.
The implementation advice for procedure Move to minimize
copying does not apply.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
