C#•3y ago

Since 'string' is a reference type, why doesn't the array update all elements with a modified string

It's more apt to say string is a value type stored on the heap

63 Replies

AngiusOP•3y ago

It is a reference type, but only due to the limitations of item size on the stack It implements pretty much the whole functionality of a value type

Pobiega•3y ago

strings are immutable in C#

triplemocha•3y ago

Interesting. I mainly tested this because later I'm going to be adding class types into an array like this, say 'class Wall'. If I use Fill, I'm concerned the array will point to just one wall instead of the intended several unique walls.

Pobiega•3y ago

correct, it would indeed fill it with the same reference you'll need to loop over the array and assign new Wall() instead

triplemocha•3y ago

I see. It's going to be a 1000x1000 array, but I guess it shouldn't take too long to loop through it and add new.

Pobiega•3y ago

it'll take a little bit, but not THAT long 🙂

triplemocha•3y ago

I tried that, but ran into this issue:

    public void FillClone(T value)
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = new T();  // I really want a clone of 'value', not the default constructor of T.  
        }

    public void FillClone(T value)
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = new T();  // I really want a clone of 'value', not the default constructor of T.  
        }

Pobiega•3y ago

then you might need to implement a clone method for T there is an interface for it that you can restrict T to be ICloneable

triplemocha•3y ago

I just want it restricted in this method.

Pobiega•3y ago

well, where is T declared? on the type that has this method? it will need to be clonable for it to work with this method, so it shouldnt change anything

triplemocha•3y ago

I ran into this problem before and ended up doing a C++ project instead. So, I really want to understand this. Ah, so something like this?

class Wall : ICloneable
{
    public bool isBreakable;

    public Wall()
    {
        isBreakable = true;
    }

    public object Clone()
    {
        return this.MemberwiseClone();
    }
}

class Wall : ICloneable
{
    public bool isBreakable;

    public Wall()
    {
        isBreakable = true;
    }

    public object Clone()
    {
        return this.MemberwiseClone();
    }
}

Pobiega•3y ago

sure as long as Wall doesnt have any reference types at all in it, that will work if you have reference types, they need to be cloned individually. deep cloning can get pretty complicated.

triplemocha•3y ago

There will be reference types in the class.

Pobiega•3y ago

ouchies 🙂 well, assuming you want those cloned too

triplemocha•3y ago

Eh, this is annoying coming from a C++ background.

Pobiega•3y ago

if you actually want them to point to the same object that value.X is, then its fine I dont see how this is different at all from cpp

triplemocha•3y ago

Maybe it's just the way I do it, without using 'new' much.

Pobiega•3y ago

public class MochaWorld
{
    private ITile[] _world = new ITile[500];

    public void Fill<T>(T value) where T : ITile, ICloneable<T>
    {
        for (int i = 0; i < _world.Length; i++)
        {
            _world[i] = value.Clone();
        }
    }
}
class Wall : ICloneable<Wall>, ITile
{
    public bool isBreakable;

    public Wall()
    {
        isBreakable = true;
    }

    public Wall Clone()
    {
        return (Wall)MemberwiseClone();
    }
}

public interface ITile
{
}

public interface ICloneable<T>
{
    T Clone();
}

public class MochaWorld
{
    private ITile[] _world = new ITile[500];

    public void Fill<T>(T value) where T : ITile, ICloneable<T>
    {
        for (int i = 0; i < _world.Length; i++)
        {
            _world[i] = value.Clone();
        }
    }
}
class Wall : ICloneable<Wall>, ITile
{
    public bool isBreakable;

    public Wall()
    {
        isBreakable = true;
    }

    public Wall Clone()
    {
        return (Wall)MemberwiseClone();
    }
}

public interface ITile
{
}

public interface ICloneable<T>
{
    T Clone();
}

something like this?

triplemocha•3y ago

Yeah, seems understandable and good to study from. Thanks. @Pobiega This comes up often:

class Wall : ICloneable<Wall>

class Wall : ICloneable<Wall>

Error: The non-generic type 'ICloneable' cannot be used with type arguments. Though this compiled fine. I changed Wall to object in Clone();

class Wall : ICloneable 
{
    public bool isBreakable;

    public Wall()
    {
        isBreakable = true;
    }

    public object Clone()
    {
        return (Wall)this.MemberwiseClone();
    }
}

class Wall : ICloneable 
{
    public bool isBreakable;

    public Wall()
    {
        isBreakable = true;
    }

    public object Clone()
    {
        return (Wall)this.MemberwiseClone();
    }
}

Pobiega•3y ago

yeah I introduced my own interface

public interface ICloneable<T>
{
    T Clone();
}

public interface ICloneable<T>
{
    T Clone();
}

since I didn't want to deal with object 😄

triplemocha•3y ago

Ah. I'm also confused with this one:

    public void FillClone<T>(T value) where T : ICloneable<T>
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = value.Clone();
        }

    public void FillClone<T>(T value) where T : ICloneable<T>
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = value.Clone();
        }

FillClone is in Array2D<T>, so adding <T> to FillClone is causing the issue here I think. It says Error: The non-generic type 'ICloneable' cannot be used with type arguments.

Pobiega•3y ago

one sec

public class Array2D<T> where T : ITile, ICloneable<T>
{
    
}

public class Array2D<T> where T : ITile, ICloneable<T>
{
    
}

just change Array2D to be like this then potentially you could remove the ITile restriction, but it will mean you can't say that your backing array is ITile I did it like this because I imagine you might want to store other things than Wall in here 🙂

triplemocha•3y ago

My Mocha World is just walls. All walls. 😆 I do want to keep Array2D generic enough so it's not just for my game project. So, I don't know if I want to say it's always a tile.

Pobiega•3y ago

sure thats fine then it will probably look like

public class Array2D<T> where T : ICloneable<T>
{
    private T[] _world = new T[500];

    public void Fill(T value)
    {
        for (int i = 0; i < _world.Length; i++)
        {
            _world[i] = value.Clone();
        }
    }
}

public class Array2D<T> where T : ICloneable<T>
{
    private T[] _world = new T[500];

    public void Fill(T value)
    {
        for (int i = 0; i < _world.Length; i++)
        {
            _world[i] = value.Clone();
        }
    }
}

triplemocha•3y ago

It worked 🙂 Prior to your last post, I'll look into it.

        map.FillClone(new Wall()); // breakable is true by default
        map.Get(1, 1).isBreakable = false; 
        Console.WriteLine(map.Get(2, 2).isBreakable); // clone outputs true

        map.FillClone(new Wall()); // breakable is true by default
        map.Get(1, 1).isBreakable = false; 
        Console.WriteLine(map.Get(2, 2).isBreakable); // clone outputs true

Yeah, that's what I did to get it to run. I don't know if I need two separate ones, but one just clones it instead of a reference copy.

        public void Fill(T value)
        {
            Array.Fill(m_array, value);
        }

        public void FillClone(T value)  
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = (T)value.Clone();
        }

        public void Fill(T value)
        {
            Array.Fill(m_array, value);
        }

        public void FillClone(T value)  
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = (T)value.Clone();
        }

Oh, I guess there could be a second argument to turn both into one. ("cloneMe")

Pobiega•3y ago

nah this is fine. if this is for some kinda library that you plan on reusing, you want a nice API to work with I'd slap some /// comments on top of each method

triplemocha•3y ago

I saved you from my comments, been removing them. I go a bit crazy with those.

Pobiega•3y ago

😄

triplemocha•3y ago

What I meant was this:

public void Fill(T value, bool clone)
        {
            if (clone)
            {
                for (int i = 0; i < GetSize(); i++)
                    m_array[i] = (T)value.Clone();
            }
            else
            {
                Array.Fill(m_array, value);
            }
        }

public void Fill(T value, bool clone)
        {
            if (clone)
            {
                for (int i = 0; i < GetSize(); i++)
                    m_array[i] = (T)value.Clone();
            }
            else
            {
                Array.Fill(m_array, value);
            }
        }

Pobiega•3y ago

please don't bool parameters like that is kind of an anti-pattern

triplemocha•3y ago

Ah. Okay.

Pobiega•3y ago

https://martinfowler.com/bliki/FlagArgument.html

triplemocha•3y ago

public void Fill(T value, bool clone, bool cloneButLast, bool cloneButFirst, bool pleaseClone)

Pobiega•3y ago

triplemocha•3y ago

Say later my Wall class has an Items container. It holds item ids. List<int> m_items = new List<int>();
Does that need any special treatement for cloning the wall, too?

Pobiega•3y ago

if you want each of those walls to have a unique list, then yes

triplemocha•3y ago

Each will need a unique list.

Pobiega•3y ago

MemberwiseClone() returns a shallow copy so you'll need to do something like...

triplemocha•3y ago

class Wall : ICloneable 
{
    public bool m_isBreakable;
    public List<int> m_Items = new List<int>();

    public Wall()
    {
        m_isBreakable = true;
    }

    public object Clone()
    {
        return this.MemberwiseClone();
    }
}

class Wall : ICloneable 
{
    public bool m_isBreakable;
    public List<int> m_Items = new List<int>();

    public Wall()
    {
        m_isBreakable = true;
    }

    public object Clone()
    {
        return this.MemberwiseClone();
    }
}

Something like this.

Pobiega•3y ago

class Wall : ICloneable 
{
    public bool m_isBreakable;
    public List<int> m_Items = new List<int>();

    public Wall()
    {
        m_isBreakable = true;
    }

    public object Clone()
    {
        var copy = (Wall)MemberwiseClone();
        copy.m_Items = new();
        return copy;
    }
}

class Wall : ICloneable 
{
    public bool m_isBreakable;
    public List<int> m_Items = new List<int>();

    public Wall()
    {
        m_isBreakable = true;
    }

    public object Clone()
    {
        var copy = (Wall)MemberwiseClone();
        copy.m_Items = new();
        return copy;
    }
}

would work, but would also not let you actually copy the list, a clone would always have an empty list welcome to the weird world of "deep cloning" you see, the problem just grows for each level of reference types you have since its a list of ints, its not too bad here

public object Clone()
{
    var copy = (Wall)MemberwiseClone();
    copy.m_Items = new();
    copy.m_Items.AddRange(m_Items);

    return copy;
}

public object Clone()
{
    var copy = (Wall)MemberwiseClone();
    copy.m_Items = new();
    copy.m_Items.AddRange(m_Items);

    return copy;
}

triplemocha•3y ago

I see, that's not too bad.

Pobiega•3y ago

yeah, but if it was a list of Item... you'd have to deepclone those too and it just keeps going

triplemocha•3y ago

I plan for Items to be a static class, which holds a list of type Item. To create a new item, it will be int myNewItemID = Items::create("genericItemLoadTag"); This saves the actual object into Items::m_items. But it returns the generated id. So, I guess in this case it'd need to store a clone of it. Most generated objects are stored in a lookup map table and is referenced by id. Luckily there's nothing further to clone with Item. I keep the data simple in it. For C#, a thought is maybe Items could be struct so it's a value type. @Pobiega Would changing all of this to struct be a good idea? I realized in C++ I was doing bitwise copies.

Pobiega•3y ago

¯\_(ツ)_/¯ this is out of my area of expertise

triplemocha•3y ago

Never used structs?

Pobiega•3y ago

not never, but very rarely I'm an enterprise web developer 😛 but sure, a record struct seems like a good idea give that a spin

triplemocha•3y ago

Ah okay. In Unity they use structs for vectors, because the garbage collector is just for classes. So bitwise copies are usually faster. I did hear in C# MS doesn't recommend structs for anything over 16kb, which seems silly. I think it's just for performance reasons. Structs are like ints, they are value types that store data like classes do, but each have their pros/cons. Anyway, I was thinking that could be an option for my Items class and forget about any deep cloning concerns.

Pobiega•3y ago

well, List is a reference type, whatever you do so you'll still need the explicit list cloning behaviour

triplemocha•3y ago

Yeah, that can get confusing with classes and structs all working together. I heard that before generics existed, structs would get casted to classes 😆 @Pobiega Is there a solution to this? Before we had class Array2D<T> where T : ICloneable but that worked for Wall. If I change the type to int it starts complaining about ICloneable.

Pobiega•3y ago

hm.. one way would be to make FillClone an extensionmethod, but then the _world array needs to be public

triplemocha•3y ago

It seems like this should work:

class Array2D<T> where T : INumber<T>, ICloneable

class Array2D<T> where T : INumber<T>, ICloneable

If it's a number or cloneable. In my perfect world, I guess.

Pobiega•3y ago

thats not how constraints work they are not "or", they are "and"

triplemocha•3y ago

That worked...

    class Array2DExt<T> : Array2D<T> where T : ICloneable
    {
        /// <summary>
        /// Fills the array with a given value.
        /// </summary>
        /// <param name="value">The value used to fill the array.</param>
        public void FillClone(T value)
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = (T)value.Clone();
        }
    }

    class Array2DExt<T> : Array2D<T> where T : ICloneable
    {
        /// <summary>
        /// Fills the array with a given value.
        /// </summary>
        /// <param name="value">The value used to fill the array.</param>
        public void FillClone(T value)
        {
            for (int i = 0; i < GetSize(); i++)
                m_array[i] = (T)value.Clone();
        }
    }

Pobiega•3y ago

that... works. its a bit awkward I guess

triplemocha•3y ago

I thought that was a method extension hah. It's been a while. I guess that's more inheritance.

Pobiega•3y ago

thats exactly what it is extension method would be to make the class static, and move the T to FillClone and pass a this Array2D<T> self argument as the first thing

static class Array2DExt
{
    /// <summary>
    /// Fills the array with a given value.
    /// </summary>
    /// <param name="value">The value used to fill the array.</param>
    public static void FillClone<T>(this Array2D<T> self, T value) where T : ICloneable
    {
        for (int i = 0; i < self.GetSize(); i++)
            self.array[i] = (T)value.Clone();
    }
}

static class Array2DExt
{
    /// <summary>
    /// Fills the array with a given value.
    /// </summary>
    /// <param name="value">The value used to fill the array.</param>
    public static void FillClone<T>(this Array2D<T> self, T value) where T : ICloneable
    {
        for (int i = 0; i < self.GetSize(); i++)
            self.array[i] = (T)value.Clone();
    }
}

as I said, the problem is the visibility of m_array

triplemocha•3y ago

That worked. I used Array2DExt.FillClone<Wall>(map, new Wall());

Pobiega•3y ago

right, thats not how you call an extension method 😄 you'd call it like map.FillClone(new Wall());

triplemocha•3y ago

Well, thanks. A bit of a pain but at least it's a sharpppp pain. Ah Umm... it can't find FillClone. Assuming it's like

        Array2D<Wall> map = new  Array2D<Wall>();

        map.Init(10, 10); 
        map.FillClone(new Wall());

        Array2D<Wall> map = new  Array2D<Wall>();

        map.Init(10, 10); 
        map.FillClone(new Wall());

Ah, forgot the 'this' in FillClone<T>() It works... like an extended method of Map.

Pobiega•3y ago

thats why they are called extension methods 🙂

triplemocha•3y ago

I never did one of those before. Horray.

Pobiega•3y ago

its just a static method, but it "behaves" as if it was a real part of the class its very idiomatic in modern c# to the point where we often add extension methods for our own types

triplemocha•3y ago

Well, thanks for the help. I think I won't be running away this time, now that I got a better understanding of "the clone wars."

Gaming

Programming

Since 'string' is a reference type, why doesn't the array update all elements with a modified string

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