wabbajack/Wabbajack.Common/ReadOnlyMemorySlice.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;

namespace Wabbajack.Common
{
    public struct ReadOnlyMemorySlice<T> : IEnumerable<T>
    {
        private T[] _arr;
        public int Length { get; private set; }

        public int StartPosition { get; private set; }

        [DebuggerStepThrough]
        public ReadOnlyMemorySlice(T[] arr)
        {
            _arr = arr;
            StartPosition = 0;
            Length = arr.Length;
        }

        [DebuggerStepThrough]
        public ReadOnlyMemorySlice(T[] arr, int startPos, int length)
        {
            _arr = arr;
            StartPosition = startPos;
            Length = length;
        }

        public ReadOnlySpan<T> Span => _arr.AsSpan(StartPosition, Length);

        public T this[int index] => _arr[index + StartPosition];

        [DebuggerStepThrough]
        public ReadOnlyMemorySlice<T> Slice(int start)
        {
            var startPos = StartPosition + start;
            if (startPos < 0) throw new ArgumentOutOfRangeException();
            return new ReadOnlyMemorySlice<T>
            {
                _arr = _arr,
                StartPosition = StartPosition + start,
                Length = Length - start
            };
        }

        [DebuggerStepThrough]
        public ReadOnlyMemorySlice<T> Slice(int start, int length)
        {
            var startPos = StartPosition + start;
            if (startPos < 0) throw new ArgumentOutOfRangeException();
            if (startPos + length > _arr.Length) throw new ArgumentOutOfRangeException();
            return new ReadOnlyMemorySlice<T>
            {
                _arr = _arr,
                StartPosition = StartPosition + start,
                Length = length
            };
        }

        public IEnumerator<T> GetEnumerator()
        {
            for (var i = 0; i < Length; i++) yield return _arr[i + StartPosition];
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

        public static implicit operator ReadOnlySpan<T>(ReadOnlyMemorySlice<T> mem)
        {
            return mem.Span;
        }

        public static implicit operator ReadOnlyMemorySlice<T>?(T[]? mem)
        {
            if (mem == null) return null;
            return new ReadOnlyMemorySlice<T>(mem);
        }

        public static implicit operator ReadOnlyMemorySlice<T>(T[] mem)
        {
            return new ReadOnlyMemorySlice<T>(mem);
        }
    }
}