c# - In an expression tree, how do I use an expression that requires a comparison to be made with the result, eg. IndexOf?

Question

I know how to do this:

    Expression body = Expression.Call(selector.Body, "Contains", null,
        Expression.Constant("cats", typeof(string)));

Since 'contains' returns true/false it's no problem.

However, how do I do IndexOf and see if the result is greater than 5?

    Expression body = Expression.Call(selector.Body, "IndexOf", null,
        Expression.Constant("cats", typeof(string)));

Answer 1

With Expression.GreaterThan:

Expression body = 
 Expression.GreaterThan(
   Expression.Call(selector.Body, "IndexOf", null, Expression.Constant("cats")),
   Expression.Constant(5)
 );