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Calling overriden method from base class constructor
f#

How to call an overriden method from base class constructor?

Following code raises "The initialization of an object or value resulted in an object or value being accessed recursively before it was fully initialized." in DerivedClass GetString

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type BaseClass = class

    abstract member GetString : unit -> string


    default this.GetString() =


        "base"

    new () as this = {} then


        let str = this.GetString()


        ()        


end

type DerivedClass() = class 


    inherit BaseClass()


    override this.GetString() =


        "overriden" // - Exception here 


end

let _ = new DerivedClass()
.

I don't think you can do this (and I think you don't want to do this). C# might allow it maybe, but it is kind of nonsense to do (and FxCop surely will complain too).

What is the real/actual scenario, or are you just curious?

By on 6/9/2010 9:47 AM ()

Thanks for reply. Yes C# allows that. The example could be a class which doing some initialization in base constructor and calls some virtual Init method. Something like

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type ClassA = class 


    abstract member Init : unit -> unit

    default this.Init() = 

        // some initialization

        ()


    new () as this = {} then

        this.Init()


end

type ClassB() = class 

    inherit ClassA()


    override this.Init() =

        base.Init()

        // some initialization

        ()


end

C#

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    public class ClassA

    {

        protected virtual void Init()

        {

        }


        public ClassA()

        {

            Init();

        }

    }


    public class ClassB : ClassA

    {

        protected override void Init()

        {

            base.Init();

        }

    }
By on 6/9/2010 10:16 AM ()

Get rid of the virtual Init method, and put the code in the base and derived constructors. Calling virtual methods from constructors is a dubious feature at best. Assuredly, the base class constructor ought not depend on derived initialization happening before some of its own.

By on 6/9/2010 11:56 AM ()

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