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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.
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.Marshalling;
using System.Runtime.Versioning;
using EditorBrowsableAttribute = System.ComponentModel.EditorBrowsableAttribute;
using EditorBrowsableState = System.ComponentModel.EditorBrowsableState;
#pragma warning disable 0809 // Obsolete member 'Span<T>.Equals(object)' overrides non-obsolete member 'object.Equals(object)'
#pragma warning disable 8500 // address / sizeof of managed types
namespace System
{
/// <summary>
/// ReadOnlySpan represents a contiguous region of arbitrary memory. Unlike arrays, it can point to either managed
/// or native memory, or to memory allocated on the stack. It is type-safe and memory-safe.
/// </summary>
[DebuggerTypeProxy(typeof(SpanDebugView<>))]
[DebuggerDisplay("{ToString(),raw}")]
[NonVersionable]
#pragma warning disable SYSLIB1056 // Specified native type is invalid
[NativeMarshalling(typeof(ReadOnlySpanMarshaller<,>))]
#pragma warning restore SYSLIB1056 // Specified native type is invalid
[Intrinsic]
public readonly ref struct ReadOnlySpan<T>
{
/// <summary>A byref or a native ptr.</summary>
internal readonly ref T _reference;
/// <summary>The number of elements this ReadOnlySpan contains.</summary>
private readonly int _length;
/// <summary>
/// Creates a new read-only span 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>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlySpan(T[]? array)
{
if (array == null)
{
this = default;
return; // returns default
}
_reference = ref MemoryMarshal.GetArrayDataReference(array);
_length = array.Length;
}
/// <summary>
/// Creates a new read-only span 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 read-only span.</param>
/// <param name="length">The number of items in the read-only span.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in the range (<0 or >Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlySpan(T[]? array, int start, int length)
{
if (array == null)
{
if (start != 0 || length != 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
this = default;
return; // returns default
}
#if TARGET_64BIT
// See comment in Span<T>.Slice for how this works.
if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)array.Length)
ThrowHelper.ThrowArgumentOutOfRangeException();
#else
if ((uint)start > (uint)array.Length || (uint)length > (uint)(array.Length - start))
ThrowHelper.ThrowArgumentOutOfRangeException();
#endif
_reference = ref Unsafe.Add(ref MemoryMarshal.GetArrayDataReference(array), (nint)(uint)start /* force zero-extension */);
_length = length;
}
/// <summary>
/// Creates a new read-only span over the target unmanaged buffer. Clearly this
/// is quite dangerous, because we are creating arbitrarily typed T's
/// out of a void*-typed block of memory. And the length is not checked.
/// But if this creation is correct, then all subsequent uses are correct.
/// </summary>
/// <param name="pointer">An unmanaged pointer to memory.</param>
/// <param name="length">The number of <typeparamref name="T"/> elements the memory contains.</param>
/// <exception cref="ArgumentException">
/// Thrown when <typeparamref name="T"/> is reference type or contains pointers and hence cannot be stored in unmanaged memory.
/// </exception>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="length"/> is negative.
/// </exception>
[CLSCompliant(false)]
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public unsafe ReadOnlySpan(void* pointer, int length)
{
if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(T));
if (length < 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
_reference = ref *(T*)pointer;
_length = length;
}
/// <summary>Creates a new <see cref="ReadOnlySpan{T}"/> of length 1 around the specified reference.</summary>
/// <param name="reference">A reference to data.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlySpan(ref readonly T reference)
{
_reference = ref Unsafe.AsRef(in reference);
_length = 1;
}
// Constructor for internal use only. It is not safe to expose publicly, and is instead exposed via the unsafe MemoryMarshal.CreateReadOnlySpan.
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal ReadOnlySpan(ref T reference, int length)
{
Debug.Assert(length >= 0);
_reference = ref reference;
_length = length;
}
/// <summary>
/// Returns the specified element of the read-only span.
/// </summary>
/// <param name="index"></param>
/// <returns></returns>
/// <exception cref="IndexOutOfRangeException">
/// Thrown when index less than 0 or index greater than or equal to Length
/// </exception>
public ref readonly T this[int index]
{
[Intrinsic]
[MethodImpl(MethodImplOptions.AggressiveInlining)]
[NonVersionable]
get
{
if ((uint)index >= (uint)_length)
ThrowHelper.ThrowIndexOutOfRangeException();
return ref Unsafe.Add(ref _reference, (nint)(uint)index /* force zero-extension */);
}
}
/// <summary>
/// The number of items in the read-only span.
/// </summary>
public int Length
{
[Intrinsic]
[NonVersionable]
get => _length;
}
/// <summary>
/// Gets a value indicating whether this <see cref="ReadOnlySpan{T}"/> is empty.
/// </summary>
/// <value><see langword="true"/> if this span is empty; otherwise, <see langword="false"/>.</value>
public bool IsEmpty
{
[NonVersionable]
get => _length == 0;
}
/// <summary>
/// Returns false if left and right point at the same memory and have the same length. Note that
/// this does *not* check to see if the *contents* are equal.
/// </summary>
public static bool operator !=(ReadOnlySpan<T> left, ReadOnlySpan<T> right) => !(left == right);
/// <summary>
/// This method is not supported as spans cannot be boxed. To compare two spans, use operator==.
/// </summary>
/// <exception cref="NotSupportedException">
/// Always thrown by this method.
/// </exception>
[Obsolete("Equals() on ReadOnlySpan will always throw an exception. Use the equality operator instead.")]
[EditorBrowsable(EditorBrowsableState.Never)]
public override bool Equals(object? obj) =>
throw new NotSupportedException(SR.NotSupported_CannotCallEqualsOnSpan);
/// <summary>
/// This method is not supported as spans cannot be boxed.
/// </summary>
/// <exception cref="NotSupportedException">
/// Always thrown by this method.
/// </exception>
[Obsolete("GetHashCode() on ReadOnlySpan will always throw an exception.")]
[EditorBrowsable(EditorBrowsableState.Never)]
public override int GetHashCode() =>
throw new NotSupportedException(SR.NotSupported_CannotCallGetHashCodeOnSpan);
/// <summary>
/// Defines an implicit conversion of an array to a <see cref="ReadOnlySpan{T}"/>
/// </summary>
public static implicit operator ReadOnlySpan<T>(T[]? array) => new ReadOnlySpan<T>(array);
/// <summary>
/// Defines an implicit conversion of a <see cref="ArraySegment{T}"/> to a <see cref="ReadOnlySpan{T}"/>
/// </summary>
public static implicit operator ReadOnlySpan<T>(ArraySegment<T> segment)
=> new ReadOnlySpan<T>(segment.Array, segment.Offset, segment.Count);
/// <summary>
/// Returns a 0-length read-only span whose base is the null pointer.
/// </summary>
public static ReadOnlySpan<T> Empty => default;
/// <summary>
/// Casts a read-only span of <typeparamref name="TDerived"/> to a read-only span of <typeparamref name="T"/>.
/// </summary>
/// <typeparam name="TDerived">The element type of the source read-only span, which must be derived from <typeparamref name="T"/>.</typeparam>
/// <param name="items">The source read-only span. No copy is made.</param>
/// <returns>A read-only span with elements cast to the new type.</returns>
/// <remarks>This method uses a covariant cast, producing a read-only span that shares the same memory as the source. The relationships expressed in the type constraints ensure that the cast is a safe operation.</remarks>
public static ReadOnlySpan<T> CastUp<TDerived>(ReadOnlySpan<TDerived> items) where TDerived : class?, T
{
return new ReadOnlySpan<T>(ref Unsafe.As<TDerived, T>(ref items._reference), items.Length);
}
/// <summary>Gets an enumerator for this span.</summary>
public Enumerator GetEnumerator() => new Enumerator(this);
/// <summary>Enumerates the elements of a <see cref="ReadOnlySpan{T}"/>.</summary>
public ref struct Enumerator
{
/// <summary>The span being enumerated.</summary>
private readonly ReadOnlySpan<T> _span;
/// <summary>The next index to yield.</summary>
private int _index;
/// <summary>Initialize the enumerator.</summary>
/// <param name="span">The span to enumerate.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Enumerator(ReadOnlySpan<T> span)
{
_span = span;
_index = -1;
}
/// <summary>Advances the enumerator to the next element of the span.</summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public bool MoveNext()
{
int index = _index + 1;
if (index < _span.Length)
{
_index = index;
return true;
}
return false;
}
/// <summary>Gets the element at the current position of the enumerator.</summary>
public ref readonly T Current
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get => ref _span[_index];
}
}
/// <summary>
/// Returns a reference to the 0th element of the Span. If the Span is empty, returns null reference.
/// It can be used for pinning and is required to support the use of span within a fixed statement.
/// </summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public ref readonly T GetPinnableReference()
{
// Ensure that the native code has just one forward branch that is predicted-not-taken.
ref T ret = ref Unsafe.NullRef<T>();
if (_length != 0) ret = ref _reference;
return ref ret;
}
/// <summary>
/// Copies the contents of this read-only span into destination span. If the source
/// and destinations overlap, this method behaves as if the original values in
/// a temporary location before the destination is overwritten.
/// </summary>
/// <param name="destination">The span to copy items into.</param>
/// <exception cref="ArgumentException">
/// Thrown when the destination Span is shorter than the source Span.
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public void CopyTo(Span<T> destination)
{
// Using "if (!TryCopyTo(...))" results in two branches: one for the length
// check, and one for the result of TryCopyTo. Since these checks are equivalent,
// we can optimize by performing the check once ourselves then calling Memmove directly.
if ((uint)_length <= (uint)destination.Length)
{
Buffer.Memmove(ref destination._reference, ref _reference, (uint)_length);
}
else
{
ThrowHelper.ThrowArgumentException_DestinationTooShort();
}
}
/// <summary>
/// Copies the contents of this read-only span into destination span. If the source
/// and destinations overlap, this method behaves as if the original values in
/// a temporary location before the destination is overwritten.
/// </summary>
/// <returns>If the destination span is shorter than the source span, this method
/// return false and no data is written to the destination.</returns>
/// <param name="destination">The span to copy items into.</param>
public bool TryCopyTo(Span<T> destination)
{
bool retVal = false;
if ((uint)_length <= (uint)destination.Length)
{
Buffer.Memmove(ref destination._reference, ref _reference, (uint)_length);
retVal = true;
}
return retVal;
}
/// <summary>
/// Returns true if left and right point at the same memory and have the same length. Note that
/// this does *not* check to see if the *contents* are equal.
/// </summary>
public static bool operator ==(ReadOnlySpan<T> left, ReadOnlySpan<T> right) =>
left._length == right._length &&
Unsafe.AreSame(ref left._reference, ref right._reference);
/// <summary>
/// For <see cref="ReadOnlySpan{Char}"/>, returns a new instance of string that represents the characters pointed to by the span.
/// Otherwise, returns a <see cref="string"/> with the name of the type and the number of elements.
/// </summary>
public override string ToString()
{
if (typeof(T) == typeof(char))
{
return new string(new ReadOnlySpan<char>(ref Unsafe.As<T, char>(ref _reference), _length));
}
return $"System.ReadOnlySpan<{typeof(T).Name}>[{_length}]";
}
/// <summary>
/// Forms a slice out of the given read-only span, beginning at 'start'.
/// </summary>
/// <param name="start">The index at which to begin this slice.</param>
/// <exception cref="ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> index is not in range (<0 or >Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlySpan<T> Slice(int start)
{
if ((uint)start > (uint)_length)
ThrowHelper.ThrowArgumentOutOfRangeException();
return new ReadOnlySpan<T>(ref Unsafe.Add(ref _reference, (nint)(uint)start /* force zero-extension */), _length - start);
}
/// <summary>
/// Forms a slice out of the given read-only span, 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="ArgumentOutOfRangeException">
/// Thrown when the specified <paramref name="start"/> or end index is not in range (<0 or >Length).
/// </exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public ReadOnlySpan<T> Slice(int start, int length)
{
#if TARGET_64BIT
// See comment in Span<T>.Slice for how this works.
if ((ulong)(uint)start + (ulong)(uint)length > (ulong)(uint)_length)
ThrowHelper.ThrowArgumentOutOfRangeException();
#else
if ((uint)start > (uint)_length || (uint)length > (uint)(_length - start))
ThrowHelper.ThrowArgumentOutOfRangeException();
#endif
return new ReadOnlySpan<T>(ref Unsafe.Add(ref _reference, (nint)(uint)start /* force zero-extension */), length);
}
/// <summary>
/// Copies the contents of this read-only span 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()
{
if (_length == 0)
return Array.Empty<T>();
var destination = new T[_length];
Buffer.Memmove(ref MemoryMarshal.GetArrayDataReference(destination), ref _reference, (uint)_length);
return destination;
}
}
}
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