Question

I’d like to pass a class property (or a getter/setter if need be) reference to a function.

For example I have an array of a class with lots of boolean flags.

class Flags
{
  public bool a;
  public bool b;
  public bool c;
  public string name;

  public Flags(bool a, bool b, bool c, string name)
  {
    this.a = a;
    this.b = b;
    this.c = c;
    this.name = name;
  }
}

I can write a method that returns all instances of Flags for which a chosen flag is true

public Flags[] getAllWhereAisTrue(Flags[] array)
{
  List<Flags> resultList = new List<Flags>();
  for (int i = 0; i < array.Length; i++)
  {
    if (array[i].a == true) // for each Flags for which a is true
    {                       // add it to the results list
      resultList.Add(array[i]);
    }
  }
  return resultList.ToArray(); //return the results list as an array
}

What would I use to allow me to pass a class property as a parameter, so as to save me from having to write this method once for each boolean property of Flags (in this example that’s three times, once for a, b and c)?

I’m trying to avoid giving Flags an array of Booleans in an attempt to keep the resulting code easy to read. I’m writing a library for use by relatively inexperienced coders.

Thank you

(With apologies if this is a dupe of Passing property as parameter in method, I can’t quite tell if it’s the same issue)

Answer 1

You could use a Func<Flags, bool> as parameter:

public Flags[] getAllWhereAisTrue(Flags[] array, Func<Flags, bool> propertySelector)
{
    List<Flags> resultList = new List<Flags>();
    for (int i = 0; i < array.Length; i++)
    {
        if (propertySelector(array[i])) // for each Flags for which a is true
        {                       // add it to the results list
            resultList.Add(array[i]);
        }
    }
    return resultList.ToArray(); //return the results list as an array
}

Then you could use it like this:

var allAFlagsSet = getAllWhereAisTrue(flagsArray, x=> x.a);

But really you should not reinvent this – Linq does this out of the box (notice the similarity):

var allAFlagsSet = flagsArray.Where(x=> x.a).ToArray();

Both solutions would require the a,b,c to be public (should really be a public property in this case)