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    <p>As far as I know, there are two separate issues here:</p> <h3>Making sure the child class' constructor calls the base class' constructor</h3> <p>You'll have to <em>explicitly</em> call the base class' constructor:</p> <pre><code>constructor TMinMatrix.Create(Rows, Cols: Byte); begin inherited; //... end; </code></pre> <h3>Making sure the child class' constructor overrides the base class' constructor</h3> <p>You'll <em>also</em> have to make the child class' constructor <code>override</code>, and the base class' constructor <code>virtual</code>, to make sure the compiler sees the relation between the two. If you don't do that, the compiler will probably warn you that TMinMatrix's constructor is "hiding" TMatrix's constructor. So, the correct code would be:</p> <pre><code>type TMatrix = class protected //... public constructor Create(Rows, Cols: Byte); virtual; // &lt;-- Added "virtual" here //... type TMinMatrix = class(TMatrix) private //... public constructor Create(Rows, Cols: Byte); override; // &lt;-- Added "override" here constructor CreateCopy(var that: TMinMatrix); destructor Destroy; override; // &lt;-- Also make the destructor "override"! end; </code></pre> <p>Note that you should also make your destructor <code>override</code>.</p> <h3>Introducing a constructor with different parameters</h3> <p>Note that you can only override a constructor with the same parameter list. If a child class needs a constructor with different parameters, and you want to prevent the base class' constructors from being called directly, you should write:</p> <pre><code>type TMyMatrix = class(TMatrix) //... public constructor Create(Rows, Cols, InitialValue: Byte); reintroduce; virtual; //... end implementation constructor TMyMatrix.Create(Rows, Cols, InitialValue: Byte); begin inherited Create(Rows, Cols); // &lt;-- Explicitly give parameters here //... end; </code></pre> <p>I hope this makes things more clear... Good luck!</p>
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    1. PONeed I to put overload or override words after the constructor declaration in derived class?
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    1. COCorrection: Normal constrcutors and not virtual, you don't need to use override on their descendants and you won't get compiler warnings about not doing so. The only (common) case of using virtual contsructors (with override) is for descendants of TComponent.
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    2. COOh, is it? Hm, I must've missed something along the way then... So, for "normal" (non-TComponent) classes, you can leave out the virtual/override stuff and still call inherited, and the whole thing'll still work?
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