c# - Generic type whose type parameter is an abstract base class -

let's have base class named animal , 2 derived classes named lion , tiger. , i'd have generic type named animallist<animal> contain members of animal. example:

var list = new animallist<animal>();  list.add(new lion()); list.add(new tiger()); 

very straightforward far there's catch...i'd base class animal abstract. is, i don't want allow instance of base class created. however, making base class abstract not surprisingly results in error cs0310 (see complete example below).

i did come solution: make base class non-abstract required , throw exception default (parameterless) constructor:

public animal() {     throw new system.notimplementedexception(); } 

but makes me feel little uneasy. is there better way?

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here's complete example illustrates scenario describe above:

// public class animal {}        // ok public abstract class animal {}  // 'abstract' keyword causes error 'cs0310'  public class lion : animal {} public class tiger : animal {}  public class animallist<t> :     animal     t : animal, new() {     public void add(t animal) {} }  class animallistdemo {     static public void main(string[] args)     {         // following statement causes:         // error cs0310 - 'animal' must non-abstract type         // public parameterless constructor in order use         // parameter 't' in generic type or method 'animallist<t>'          var list = new animallist<animal>();          list.add(new lion());         list.add(new tiger());     } } 

just remove new() constraint. requires provide class can instantiated through new() (which requirement about), abstract class can't this.

from msdn:

the new constraint specifies type argument in generic class declaration must have public parameterless constructor. to use new constraint, type cannot abstract.