Question

I’ve got the following method:

public static List<string> GetArgsListStartsWith(string filter, bool invertSelection, bool lowercaseArgs)
{
    return GetArgumentsList(lowercaseArgs)
          .Where(x => !invertSelection && x.StartsWith(filter)).ToList();
}

And then I call it like this GetArgsListStartsWith("/", true, false)

That would translate to: get a list of all arguments that do not start with “/”.
The problem is that the list doesn’t get populated, even if all arguments do not start with “/”.

If I call GetArgsListStartsWith("/", false, false) which translates to: get a list of all arguments which start with “/”, the list does get populated with the arguments that start with “/”.

I suspect that !invertSelection && x.StartsWith(filter) doesn’t return true when invertSelection is set to true and x.StartsWith(filter) returns false, but I do not understand why. Does anyone see something I don’t?

Answer 1

As other answers have said, your condition will only ever return true when invertSelection is false.

The simplest way of conditionally inverting a result is to use the XOR operator:

.Where(x => x.StartsWith(filter) ^ invertSelection)

I prefer this over lc’s solution as it only specifies the StartsWith once.