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    <p>Here's a different version which stores the Item (not its access) in the Vector. It works by using inheritance, creating a Vector of a base type. That implies an Indefinite_Vector because the size of each individual component is not known in advance.</p> <p>Again, compiled but untested.</p> <pre><code>with Ada.Containers.Indefinite_Vectors; package Boxed_Base is type Base_Item is tagged record null; end record; package Item_Vectors is new Ada.Containers.Indefinite_Vectors (Index_Type =&gt; Natural, Element_Type =&gt; Base_Item'Class); use Item_Vectors; type Vector_Ptr is access Vector; end Boxed_Base; </code></pre> <p>This base type has the property that it can be stored in the vector, and have its storage management handled by Indefinite_Vectors. Now we can inherit from it, with the characteristics we need.</p> <pre><code>with Ada.Strings.Wide_Unbounded; use Ada.Strings.Wide_Unbounded; with Ada.Unchecked_Deallocation; with Boxed_Base; package Boxed_Types is type UInteger_64 is new integer; type Green_Task_Ptr is access UInteger_64; -- these two because original testcase was incomplete type String_Ptr is access Unbounded_Wide_String; type Type_T is (T_Null, T_UInt64, T_Text, T_Bool, T_GTask, T_Vector); type Item (IType : Type_T ) is new Boxed_Base.Base_Item with record case IType is when T_Null =&gt; null; when T_UInt64 =&gt; UInt64 : UInteger_64; when T_Text =&gt; String : String_Ptr; when T_Bool =&gt; Bool : Boolean; when T_GTask =&gt; Green_Task : Green_Task_Ptr; when T_Vector =&gt; Item_Vector : Boxed_Base.Vector_Ptr; end case; end record; end Boxed_Types; </code></pre> <p>One feature of the original design has gone : the default discriminant is not allowed for tagged types : that means that you create an instance with a definite discriminant (and thus a definite size!) and cannot modify it later (just replace the object with a new one).</p> <p>Another feature <em>may</em> be worth mentioning : Indefinite_Vectors may have a performance penalty over their Definite cousins : if so, that is the necessary cost incurred by heterogeneous object sizes and will pop up in some form however you slice the problem.</p> <p>It would also be possible to eliminate the discriminant Type_T by creating different subclasses for each type of Item; maybe a cleaner design but at this stage that is more refactoring than you probably want!</p>
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    1. USBrian Drummond
    1. USBrian Drummond
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    1. COI will test all three suggestions for their performance implications and mark this one as answer because it gives most detailed explanation. All answers were very helpful to me. Thanks a lot!
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      1. USEric '3ToedSloth'
 

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