Can I use an IEnumerable with different properties for each entry as a method argument?

Question

I'm relatively new to C#. I'm trying to use an IEnumerable collection as an argument to a C# function, but I want to define the properties that I want to return as well.

Suppose I have a car IEnumerable with properties such as color and brand. Each entry has a color and a brand, of course. I'm trying to split the enumerable information on the function below.

Is something like this possible?

public string stringforeach(IEnumerable coll, <<color>>, <<brand>>)
    {
        string write = "";
        int i = 0;
        foreach (var element in coll)
        {

            write += string.Concat(i.ToString() + ";" + element.color+ ";" + element.bramd + "\n");
            i++;
        }

     

        return write;
    }

Answer 1

Use two separate features of C#:

Use generics so that the method can accept collections of a specific type with the compiler knowing about the specific type being used for a specific call of the method.

Use delegates as parameters to be able to pass functions (or lambda expressions) to specify which property of an object to access.

public string StringForeach<T>(IEnumerable<T> coll, Func<T, string> property1, Func<T, string> property2)
{
    string write = "";
    int i = 0;
    foreach (var element in coll)
    {
        write += i + ";" + property1(element) + ";" + property2(element) + "\n";
        i++;
    }

    return write;
}

Given the following Car class

public class Car
{
    public string Color { get; set; }
    public string Brand { get; set; }
}

you can call the method like this:

List<Car> cars = new List<Car>();
cars.Add(new Car { Color = "Red", Brand = "BMW" });
cars.Add(new Car { Color = "Black", Brand = "Mercedes" });

string text = StringForeach<Car>(cars, c => c.Color, c => c.Brand);

---

Some explanations:

public string StringForeach<T>(IEnumerable<T> coll, Func<T, string> property1, Func<T, string> property2)

This declares a generic method which can be called with a specific type T. It accepts three parameters:

• IEnumerable<T> coll: A collection of objects of type T
• Func<T, string> property1: A delegate to a function that accepts an argument of type T and returns a string
• Func<T, string> property2: See above.

When calling the method

string text = StringForeach<Car>(cars, c => c.Color, c => c.Brand);

we specify that we call the method with type T being the concrete type Car.

The lambda expression

c => c.Color

is a short form of writing a function delegate for this function:

string SomeFunc(Car c) 
{
  return c.Color;
}

---

The Bars object from the API implements IEnumerable. In order to convert this into the type IEnumerable<Bar>, you can use this syntax:

IEnumerable bars = MarketData.GetBars();
IEnumerable<Bar> typedBars = bars.Cast<Bar>();

You can then call the method like this:

string text = StringForeach<Bar>(typedBars, c => c.OpenTime, c => c.Low);

---

Because the properties you want to use are not of type string directly, change the syntax like this:

public string StringForeach<T>(IEnumerable<T> coll, Func<T, object> property1, Func<T, object> property2)
{
    string write = "";
    int i = 0;
    foreach (var element in coll)
    {
        write += i + ";" + property1(element) + ";" + property2(element) + "\n";
        i++;
    }

    return write;
}

String conversion happens automatically.