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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 pragma Preelaborate is replaced with pragma Pure.
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;
The type Tree needs finalization if and only if type Element_Type needs finalization.
The allocation of internal storage includes a check that the capacity is not exceeded, and Capacity_Error is raised if this check fails.
In procedure Assign, if Source length is greater than Target capacity, then Capacity_Error is propagated.
Function Copy is declared as follows: 
  function Copy (Source : Tree; Capacity : Count_Type := 0)
     return Tree;
If Capacity is 0, then the tree capacity is the count of Source; if Capacity is equal to or greater than Source.Count, the tree capacity equals the value of the Capacity parameter; otherwise, the operation propagates Capacity_Error.
In the five-parameter procedure Splice_Subtree, if Source is not the same object as Target, and if the sum of Target.Count and Subtree_Node_Count (Position) is greater than Target.Capacity, then Splice_Subtree propagates Capacity_Error.
In the five-parameter procedure Splice_Children, if Source is not the same object as Target, and if the sum of Target.Count and Subtree_Node_Count (Source_Parent)-1 is greater than Target.Capacity, then Splice_Children propagates Capacity_Error. 

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. 

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