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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>
/// Span 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(SpanMarshaller<,>))]
#pragma warning restore SYSLIB1056 // Specified native type is invalid
[Intrinsic]
public readonly ref struct Span<T>
{
/// <summary>A byref or a native ptr.</summary>
internal readonly ref T _reference;
/// <summary>The number of elements this Span contains.</summary>
private readonly int _length;
/// <summary>
/// Creates a new 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>
/// <exception cref="ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Span(T[]? array)
{
if (array == null)
{
this = default;
return; // returns default
}
if (!typeof(T).IsValueType && array.GetType() != typeof(T[]))
ThrowHelper.ThrowArrayTypeMismatchException();
_reference = ref MemoryMarshal.GetArrayDataReference(array);
_length = array.Length;
}
/// <summary>
/// Creates a new 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 span.</param>
/// <param name="length">The number of items in the span.</param>
/// <remarks>Returns default when <paramref name="array"/> is null.</remarks>
/// <exception cref="ArrayTypeMismatchException">Thrown when <paramref name="array"/> is covariant and array's type is not exactly T[].</exception>
/// <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 Span(T[]? array, int start, int length)
{
if (array == null)
{
if (start != 0 || length != 0)
ThrowHelper.ThrowArgumentOutOfRangeException();
this = default;
return; // returns default
}
if (!typeof(T).IsValueType && array.GetType() != typeof(T[]))
ThrowHelper.ThrowArrayTypeMismatchException();
#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 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 Span(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="Span{T}"/> of length 1 around the specified reference.</summary>
/// <param name="reference">A reference to data.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Span(ref T reference)
{
_reference = ref reference;
_length = 1;
}
// Constructor for internal use only. It is not safe to expose publicly, and is instead exposed via the unsafe MemoryMarshal.CreateSpan.
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal Span(ref T reference, int length)
{
Debug.Assert(length >= 0);
_reference = ref reference;
_length = length;
}
/// <summary>
/// Returns a reference to specified element of the 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 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 span.
/// </summary>
public int Length
{
[Intrinsic]
[NonVersionable]
get => _length;
}
/// <summary>
/// Gets a value indicating whether this <see cref="Span{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 !=(Span<T> left, Span<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 Span 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 Span 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="Span{T}"/>
/// </summary>
public static implicit operator Span<T>(T[]? array) => new Span<T>(array);
/// <summary>
/// Defines an implicit conversion of a <see cref="ArraySegment{T}"/> to a <see cref="Span{T}"/>
/// </summary>
public static implicit operator Span<T>(ArraySegment<T> segment) =>
new Span<T>(segment.Array, segment.Offset, segment.Count);
/// <summary>
/// Returns an empty <see cref="Span{T}"/>
/// </summary>
public static Span<T> Empty => default;
/// <summary>Gets an enumerator for this span.</summary>
public Enumerator GetEnumerator() => new Enumerator(this);
/// <summary>Enumerates the elements of a <see cref="Span{T}"/>.</summary>
public ref struct Enumerator
{
/// <summary>The span being enumerated.</summary>
private readonly Span<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(Span<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 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 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>
/// Clears the contents of this span.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public unsafe void Clear()
{
if (RuntimeHelpers.IsReferenceOrContainsReferences<T>())
{
SpanHelpers.ClearWithReferences(ref Unsafe.As<T, IntPtr>(ref _reference), (uint)_length * (nuint)(sizeof(T) / sizeof(nuint)));
}
else
{
SpanHelpers.ClearWithoutReferences(ref Unsafe.As<T, byte>(ref _reference), (uint)_length * (nuint)sizeof(T));
}
}
/// <summary>
/// Fills the contents of this span with the given value.
/// </summary>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public unsafe void Fill(T value)
{
SpanHelpers.Fill(ref _reference, (uint)_length, value);
}
/// <summary>
/// Copies the contents of this 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 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>
/// <returns>If the destination span is shorter than the source span, this method
/// return false and no data is written to the destination.</returns>
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 ==(Span<T> left, Span<T> right) =>
left._length == right._length &&
Unsafe.AreSame(ref left._reference, ref right._reference);
/// <summary>
/// Defines an implicit conversion of a <see cref="Span{T}"/> to a <see cref="ReadOnlySpan{T}"/>
/// </summary>
public static implicit operator ReadOnlySpan<T>(Span<T> span) =>
new ReadOnlySpan<T>(ref span._reference, span._length);
/// <summary>
/// For <see cref="Span{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.Span<{typeof(T).Name}>[{_length}]";
}
/// <summary>
/// Forms a slice out of the given 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 Span<T> Slice(int start)
{
if ((uint)start > (uint)_length)
ThrowHelper.ThrowArgumentOutOfRangeException();
return new Span<T>(ref Unsafe.Add(ref _reference, (nint)(uint)start /* force zero-extension */), _length - start);
}
/// <summary>
/// Forms a slice out of the given 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 Span<T> Slice(int start, int length)
{
#if TARGET_64BIT
// Since start and length are both 32-bit, their sum can be computed across a 64-bit domain
// without loss of fidelity. The cast to uint before the cast to ulong ensures that the
// extension from 32- to 64-bit is zero-extending rather than sign-extending. The end result
// of this is that if either input is negative or if the input sum overflows past Int32.MaxValue,
// that information is captured correctly in the comparison against the backing _length field.
// We don't use this same mechanism in a 32-bit process due to the overhead of 64-bit arithmetic.
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 Span<T>(ref Unsafe.Add(ref _reference, (nint)(uint)start /* force zero-extension */), length);
}
/// <summary>
/// Copies the contents of this 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>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
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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