How can I create an expression that either throws an exception or returns a value based on a condition?

Question

I'm struggling to build an expression that if the condition is true throws an exception and if it's false that it should return a value but I'm always getting the ArgumentException:

var expr =
    Expression.Condition(
        Expression.Equal(Expression.Constant(0), Expression.Constant(0)),
        Expression.Throw(Expression.Constant(new DivideByZeroException())),
        Expression.Constant(1));
var lambda = Expression.Lambda<Func<int>>(expr);
var result = lambda.Compile()();

If I put Expression.Empty() as the third argument of the Condition it then runs but I don't get the desired result if the condition is false.

Answer 1

This does it.

var expr =
    Expression.Block(
        Expression.IfThen(
            Expression.Equal(Expression.Constant(1), Expression.Constant(1)),
            Expression.Throw(
                Expression.New(typeof(DivideByZeroException))
            )
        ),
        Expression.Constant(1)
    );
var lambda = Expression.Lambda<Func<int>>(expr);
var result = lambda.Compile()();

Conditional is more similar to the ternary operator. So what you were writing was more equivalent to in C#:

return (0 == 0) ? throw new DivideByZeroException() : 1;

I changed your constant exception to a dynamically created one, I'm assuming that is preferred.