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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Buffers;
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using EditorBrowsableAttribute = System.ComponentModel.EditorBrowsableAttribute;
using EditorBrowsableState = System.ComponentModel.EditorBrowsableState;
#if !FEATURE_PORTABLE_SPAN
using Internal.Runtime.CompilerServices;
#endif // FEATURE_PORTABLE_SPAN
namespace System
{
/// <summary>
/// Represents a contiguous region of memory, similar to <see cref="ReadOnlySpan{T}"/>.
/// Unlike <see cref="ReadOnlySpan{T}"/>, it is not a byref-like type.
/// </summary>
[DebuggerDisplay("{DebuggerDisplay,nq}")]
[DebuggerTypeProxy(typeof(MemoryDebugView<>))]
public readonly struct ReadOnlyMemory<T>
{
// NOTE: With the current implementation, Memory<T> and ReadOnlyMemory<T> must have the same layout,
// as code uses Unsafe.As to cast between them.
// The highest order bit of _index is used to discern whether _object is an array/string or an owned memory
// if (_index >> 31) == 1, _object is an OwnedMemory<T>
// else, _object is a T[] or string
private readonly object _object;
private readonly int _index;
private readonly int _length;
internal const int RemoveOwnedFlagBitMask = 0x7FFFFFFF;
/// <summary>
/// Creates a new memory over the entirety of the target array.
/// </summary>
/// <param name="array">The target array.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlyMemory(T[] array)
{
if (array == null)
{
this = default;
return; // returns default
}
_object = array;
_index = 0;
_length = array.Length;
}
/// <summary>
/// Creates a new memory over the portion of the target array beginning
/// at 'start' index and ending at 'end' index (exclusive).
/// </summary>
/// <param name="array">The target array.</param>
/// <param name="start">The index at which to begin the memory.</param>
/// <param name="length">The number of items in the memory.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="System.ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in the range (<0 or >=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlyMemory(T[] array, int start, int length)
{
if (array == null)
{
if (start != 0 || length != 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
this = default;
return; // returns default
}
if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
ThrowHelper.ThrowArgumentOutOfRangeException();
_object = array;
_index = start;
_length = length;
}
/// <summary>Creates a new memory over the existing object, start, and length. No validation is performed.</summary>
/// <param name="obj">The target object.</param>
/// <param name="start">The index at which to begin the memory.</param>
/// <param name="length">The number of items in the memory.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal ReadOnlyMemory(object obj, int start, int length)
{
// No validation performed; caller must provide any necessary validation.
_object = obj;
_index = start;
_length = length;
}
//Debugger Display = {T[length]}
private string DebuggerDisplay => string.Format("{{{0}[{1}]}}", typeof(T).Name, _length);
/// <summary>
/// Defines an implicit conversion of an array to a <see cref="ReadOnlyMemory{T}"/>
/// </summary>
public static implicit operator ReadOnlyMemory<T>(T[] array) => new ReadOnlyMemory<T>(array);
/// <summary>
/// Defines an implicit conversion of a <see cref="ArraySegment{T}"/> to a <see cref="ReadOnlyMemory{T}"/>
/// </summary>
public static implicit operator ReadOnlyMemory<T>(ArraySegment<T> arraySegment) => new ReadOnlyMemory<T>(arraySegment.Array, arraySegment.Offset, arraySegment.Count);
/// <summary>
/// Returns an empty <see cref="ReadOnlyMemory{T}"/>
/// </summary>
public static ReadOnlyMemory<T> Empty => default;
/// <summary>
/// The number of items in the memory.
/// </summary>
public int Length => _length;
/// <summary>
/// Returns true if Length is 0.
/// </summary>
public bool IsEmpty => _length == 0;
/// <summary>
/// Forms a slice out of the given memory, beginning at 'start'.
/// </summary>
/// <param name="start">The index at which to begin this slice.</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> index is not in range (<0 or >=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlyMemory<T> Slice(int start)
{
if ((uint)start > (uint)_length)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
}
return new ReadOnlyMemory<T>(_object, _index + start, _length - start);
}
/// <summary>
/// Forms a slice out of the given memory, beginning at 'start', of given length
/// </summary>
/// <param name="start">The index at which to begin this slice.</param>
/// <param name="length">The desired length for the slice (exclusive).</param>
/// <exception cref="System.ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in range (<0 or >=Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlyMemory<T> Slice(int start, int length)
{
if ((uint)start > (uint)_length || (uint)length > (uint)(_length - start))
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.start);
}
return new ReadOnlyMemory<T>(_object, _index + start, length);
}
/// <summary>
/// Returns a span from the memory.
/// </summary>
public ReadOnlySpan<T> Span
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get
{
if (_index < 0)
{
return ((OwnedMemory<T>)_object).Span.Slice(_index & RemoveOwnedFlagBitMask, _length);
}
else if (typeof(T) == typeof(char) && _object is string s)
{
#if FEATURE_PORTABLE_SPAN
return new ReadOnlySpan<T>(Unsafe.As<Pinnable<T>>(s), MemoryExtensions.StringAdjustment, s.Length).Slice(_index, _length);
#else
return new ReadOnlySpan<T>(ref Unsafe.As<char, T>(ref s.GetRawStringData()), s.Length).Slice(_index, _length);
#endif // FEATURE_PORTABLE_SPAN
}
else if (_object != null)
{
return new ReadOnlySpan<T>((T[])_object, _index, _length);
}
else
{
return default;
}
}
}
/// <summary>
/// Copies the contents of the read-only memory into the destination. If the source
/// and destination overlap, this method behaves as if the original values are in
/// a temporary location before the destination is overwritten.
///
/// <param name="destination">The Memory to copy items into.</param>
/// <exception cref="System.ArgumentException">
/// Thrown when the destination is shorter than the source.
/// </exception>
/// </summary>
public void CopyTo(Memory<T> destination) => Span.CopyTo(destination.Span);
/// <summary>
/// Copies the contents of the readonly-only memory into the destination. If the source
/// and destination overlap, this method behaves as if the original values are in
/// a temporary location before the destination is overwritten.
///
/// <returns>If the destination is shorter than the source, this method
/// return false and no data is written to the destination.</returns>
/// </summary>
/// <param name="destination">The span to copy items into.</param>
public bool TryCopyTo(Memory<T> destination) => Span.TryCopyTo(destination.Span);
/// <summary>Creates a handle for the memory.</summary>
/// <param name="pin">
/// If pin is true, the GC will not move the array until the returned <see cref="MemoryHandle"/>
/// is disposed, enabling the memory's address can be taken and used.
/// </param>
public unsafe MemoryHandle Retain(bool pin = false)
{
MemoryHandle memoryHandle = default;
if (pin)
{
if (_index < 0)
{
memoryHandle = ((OwnedMemory<T>)_object).Pin((_index & RemoveOwnedFlagBitMask) * Unsafe.SizeOf<T>());
}
else if (typeof(T) == typeof(char) && _object is string s)
{
GCHandle handle = GCHandle.Alloc(s, GCHandleType.Pinned);
#if FEATURE_PORTABLE_SPAN
void* pointer = Unsafe.Add<T>((void*)handle.AddrOfPinnedObject(), _index);
#else
void* pointer = Unsafe.Add<T>(Unsafe.AsPointer(ref s.GetRawStringData()), _index);
#endif // FEATURE_PORTABLE_SPAN
memoryHandle = new MemoryHandle(null, pointer, handle);
}
else if (_object is T[] array)
{
var handle = GCHandle.Alloc(array, GCHandleType.Pinned);
#if FEATURE_PORTABLE_SPAN
void* pointer = Unsafe.Add<T>((void*)handle.AddrOfPinnedObject(), _index);
#else
void* pointer = Unsafe.Add<T>(Unsafe.AsPointer(ref array.GetRawSzArrayData()), _index);
#endif // FEATURE_PORTABLE_SPAN
memoryHandle = new MemoryHandle(null, pointer, handle);
}
}
else
{
if (_index < 0)
{
((OwnedMemory<T>)_object).Retain();
memoryHandle = new MemoryHandle((OwnedMemory<T>)_object);
}
}
return memoryHandle;
}
/// <summary>
/// Copies the contents from the memory into a new array. This heap
/// allocates, so should generally be avoided, however it is sometimes
/// necessary to bridge the gap with APIs written in terms of arrays.
/// </summary>
public T[] ToArray() => Span.ToArray();
/// <summary>Determines whether the specified object is equal to the current object.</summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public override bool Equals(object obj)
{
if (obj is ReadOnlyMemory<T> readOnlyMemory)
{
return Equals(readOnlyMemory);
}
else if (obj is Memory<T> memory)
{
return Equals(memory);
}
else
{
return false;
}
}
/// <summary>
/// Returns true if the memory points to the same array and has the same length. Note that
/// this does *not* check to see if the *contents* are equal.
/// </summary>
public bool Equals(ReadOnlyMemory<T> other)
{
return
_object == other._object &&
_index == other._index &&
_length == other._length;
}
/// <summary>Returns the hash code for this <see cref="ReadOnlyMemory{T}"/></summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public override int GetHashCode()
{
return _object != null ? CombineHashCodes(_object.GetHashCode(), _index.GetHashCode(), _length.GetHashCode()) : 0;
}
private static int CombineHashCodes(int left, int right)
{
return ((left << 5) + left) ^ right;
}
private static int CombineHashCodes(int h1, int h2, int h3)
{
return CombineHashCodes(CombineHashCodes(h1, h2), h3);
}
/// <summary>Gets the state of the memory as individual fields.</summary>
/// <param name="start">The offset.</param>
/// <param name="length">The count.</param>
/// <returns>The object.</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal object GetObjectStartLength(out int start, out int length)
{
start = _index;
length = _length;
return _object;
}
}
}
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