C# generic constraints [duplicate]

Answer 1

It is not possible to restrict a generic argument to specific types.

As a workaround, you could provide a method for each type and forward the method calls to a common implementation:

public class Expression {

    public bool EvaluateToBool() {
        return Evaluate();
    }

    public int EvaluateToInt32() {
        return Evaluate();
    }

    private T Evaluate() {
        return default(T);
    }
}

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On the other hand, have you thought about encoding the type the expression evaluates to in the Expression type? E.g.

public abstract class Expression {

    public abstract T Evaluate();
}

public sealed class AddExpression : Expression {

    public AddExpression(Expression left, Expression right) {
        this.Left = left;
        this.Right = right;
    }

    public Expression Left { get; private set; }

    public Expression Right { get; private set; }

    public override int Evaluate() {
        return this.Left.Evaluate() + this.Right.Evaluate();
    }
}