C#•2y ago

❔ How can I create a fill method that creates unique elements?

I have the following 2D array method that is for basic types and references.

        /// <summary>
        /// Fills the array with the given value.
        /// </summary>
        /// <param name="value">The value to fill with.</param>
        public void Fill(T value)
        {
            Array.Fill(m_array, value);
        }

        /// <summary>
        /// Fills the array with the given value.
        /// </summary>
        /// <param name="value">The value to fill with.</param>
        public void Fill(T value)
        {
            Array.Fill(m_array, value);
        }

This works when I want basic types and every reference value pointing to the same object. I want to keep this method for those, which is the most common. However, I need a similar one that makes every element unique using new. For example, every Wall object in the array is unique. Each wall has its own properties. I do want the method generic so it allows any object of a class. Here's the idea:

        /// <summary>
        /// Fills the array with unique values.
        /// </summary> 
       public void FillNew(T value)
        { 
            for (int i = 0; i < Size; i++)
                m_array[i] = new T(value); 
        }

        /// <summary>
        /// Fills the array with unique values.
        /// </summary> 
       public void FillNew(T value)
        { 
            for (int i = 0; i < Size; i++)
                m_array[i] = new T(value); 
        }

Again, this is just example code of what I want to see happen, but it has a compile error that T does not have a new() constraint. Is there a good solution to this? For reference, my class is written as this:

    class Array2D<T>
    {
        private T[] m_array;
        private int m_width, m_height;

    class Array2D<T>
    {
        private T[] m_array;
        private int m_width, m_height;

15 Replies

cap5lut•2y ago

i would just give it a a factory method:

public void Fill(Func<T> factory)
{
  for (int i = 0; i < Size; i++)
    m_array[i] = factory.Invoke();
}

public void Fill(Func<T> factory)
{
  for (int i = 0; i < Size; i++)
    m_array[i] = factory.Invoke();
}

triplemochaOP•2y ago

@cap5lut I'm not familiar with factory methods in C#. I used your code, changed Fill to FillNew to separate it for now, and tried FillNew(new A()), and it said it can't convert A to System.Func<A>.

ero•2y ago

(the .Invoke() is a bit more verbose than necessary, factory() will work)

cap5lut•2y ago

u would either have to pass a lambda expression () => new A() or pass a method:

public class Example
{
  A StaticMethod()
  {
    return new A();
  }

  A InstanceMethod()
  {
    return new A();
  }
}

blah.FillNew(Example.StaticMethod);

var o = new Example();
blah.FillNew(o.InstanceMethod);

public class Example
{
  A StaticMethod()
  {
    return new A();
  }

  A InstanceMethod()
  {
    return new A();
  }
}

blah.FillNew(Example.StaticMethod);

var o = new Example();
blah.FillNew(o.InstanceMethod);

tbh i usually dont use the short version because it sorta feels wrong reading that, u could call the parameter create or createInstance and call it the short way, but then the parameter name feels weird. personal opinion ;p

triplemochaOP•2y ago

This compiled: map.FillNew(() => new A()); Not much luck with the InstanceMethod one.

cap5lut•2y ago

can u show how u tried it with the instance method? and the error itself ;p

triplemochaOP•2y ago

class A
{
    public int a;

    public A()
    {
        a = 0;
    }

    public static A InstanceMethod()
    {
        return new A();
    }
}

class A
{
    public int a;

    public A()
    {
        a = 0;
    }

    public static A InstanceMethod()
    {
        return new A();
    }
}

map.FillNew(A.InstanceMethod()); And Cannot convert from 'A' to 'System.Func<A>' Oh, I changed A.InstanceMethod() to A.InstanceMethod and it worked.

cap5lut•2y ago

u r trying to execute the method, not passing the method

triplemochaOP•2y ago

Parenthesis felt natural 🙂 I see.

cap5lut•2y ago

yeah, no ;p also, ur InstanceMethod is a static method, not an instance one ;p instance method -> an instance for the method (this) exists. static method -> is bound to the type itself, an instance does not exist

triplemochaOP•2y ago

The alternative would have been this, which seemed odd to create a new instance.

      A a = new A();
        map.FillNew(a.InstanceMethod);

      A a = new A();
        map.FillNew(a.InstanceMethod);

cap5lut•2y ago

well u could have done something like

public class Factory
{
  public int Min { get; set; }
  public int Max { get; set; }

  public A CreateInstance()
  {
    return new A(Random.Shared.Next(min, max));
  }
}

var factory = new Factory() { Min = 10, Max = 1000 };
blah.FillNew(factory.CreateInstance);

public class Factory
{
  public int Min { get; set; }
  public int Max { get; set; }

  public A CreateInstance()
  {
    return new A(Random.Shared.Next(min, max));
  }
}

var factory = new Factory() { Min = 10, Max = 1000 };
blah.FillNew(factory.CreateInstance);

basically to vary some values, or even give it more complex logic

triplemochaOP•2y ago

I see. I don't think I want a general factory class for every game class though (Wall, Floor, Cat, etc.). That can get big for my game with several CreateInstance's of each class. But at least I know several ways of doing it, and it depends on what I need of course. I'll be using all of these, I'm sure. Thanks for the help!

cap5lut•2y ago

ignore the following if its too overwhelming: u could create a factory method factory class xD

public static class Factory
{
  public static Func<Wall> CreateWallFactory(int minWidth, int maxWidth)
  {
    return () => new Wall(Random.Shared.Next(minWidth, maxWidth));
  }
  // similar for other entities
}

public static class Factory
{
  public static Func<Wall> CreateWallFactory(int minWidth, int maxWidth)
  {
    return () => new Wall(Random.Shared.Next(minWidth, maxWidth));
  }
  // similar for other entities
}

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ How can I create a fill method that creates unique elements?