ListProvider.cs

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using System.Collections;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq.Expressions;
 
namespace System.Dynamic.Utils;
 
internal abstract class ListProvider<T> : IList<T>, ICollection<T>, IEnumerable<T>, IEnumerable where T : class
{
    protected abstract T First { get; }
 
    protected abstract int ElementCount { get; }
 
    public T this[int index]
    {
        get
        {
            if (index == 0)
            {
                return First;
            }
            return GetElement(index);
        }
        [ExcludeFromCodeCoverage(Justification = "Unreachable")]
        set
        {
            throw ContractUtils.Unreachable;
        }
    }
 
    public int Count => ElementCount;
 
    [ExcludeFromCodeCoverage(Justification = "Unreachable")]
    public bool IsReadOnly => true;
 
    protected abstract T GetElement(int index);
 
    public int IndexOf(T item)
    {
        if (First == item)
        {
            return 0;
        }
        int i = 1;
        for (int elementCount = ElementCount; i < elementCount; i++)
        {
            if (GetElement(i) == item)
            {
                return i;
            }
        }
        return -1;
    }
 
    [ExcludeFromCodeCoverage(Justification = "Unreachable")]
    public void Insert(int index, T item)
    {
        throw ContractUtils.Unreachable;
    }
 
    [ExcludeFromCodeCoverage(Justification = "Unreachable")]
    public void RemoveAt(int index)
    {
        throw ContractUtils.Unreachable;
    }
 
    [ExcludeFromCodeCoverage(Justification = "Unreachable")]
    public void Add(T item)
    {
        throw ContractUtils.Unreachable;
    }
 
    [ExcludeFromCodeCoverage(Justification = "Unreachable")]
    public void Clear()
    {
        throw ContractUtils.Unreachable;
    }
 
    public bool Contains(T item)
    {
        return IndexOf(item) != -1;
    }
 
    public void CopyTo(T[] array, int index)
    {
        ContractUtils.RequiresNotNull(array, "array");
        if (index < 0)
        {
            throw Error.ArgumentOutOfRange("index");
        }
        int elementCount = ElementCount;
        if (index + elementCount > array.Length)
        {
            throw new ArgumentException();
        }
        array[index++] = First;
        for (int i = 1; i < elementCount; i++)
        {
            array[index++] = GetElement(i);
        }
    }
 
    [ExcludeFromCodeCoverage(Justification = "Unreachable")]
    public bool Remove(T item)
    {
        throw ContractUtils.Unreachable;
    }
 
    public IEnumerator<T> GetEnumerator()
    {
        yield return First;
        int i = 1;
        for (int j = ElementCount; i < j; i++)
        {
            yield return GetElement(i);
        }
    }
 
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }
}