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@tarekgh @stephentoub @jkotas
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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.Diagnostics;
using System.Runtime.CompilerServices;
namespace System
{
/// <summary>Represent a range has start and end indexes.</summary>
/// <remarks>
/// Range is used by the C# compiler to support the range syntax.
/// <code>
/// int[] someArray = new int[5] { 1, 2, 3, 4, 5 };
/// int[] subArray1 = someArray[0..2]; // { 1, 2 }
/// int[] subArray2 = someArray[1..^0]; // { 2, 3, 4, 5 }
/// </code>
/// </remarks>
public readonly struct Range : IEquatable<Range>
{
/// <summary>Represent the inclusive start index of the Range.</summary>
public Index Start { get; }
/// <summary>Represent the exclusive end index of the Range.</summary>
public Index End { get; }
/// <summary>Construct a Range object using the start and end indexes.</summary>
/// <param name="start">Represent the inclusive start index of the range.</param>
/// <param name="end">Represent the exclusive end index of the range.</param>
public Range(Index start, Index end)
{
Start = start;
End = end;
}
/// <summary>Indicates whether the current Range object is equal to another object of the same type.</summary>
/// <param name="value">An object to compare with this object</param>
public override bool Equals(object? value)
{
if (value is Range)
{
Range r = (Range)value;
return r.Start.Equals(Start) && r.End.Equals(End);
}
return false;
}
/// <summary>Indicates whether the current Range object is equal to another Range object.</summary>
/// <param name="other">An object to compare with this object</param>
public bool Equals(Range other) => other.Start.Equals(Start) && other.End.Equals(End);
/// <summary>Returns the hash code for this instance.</summary>
public override int GetHashCode()
{
return HashCode.Combine(Start.GetHashCode(), End.GetHashCode());
}
/// <summary>Converts the value of the current Range object to its equivalent string representation.</summary>
public override string ToString()
{
Span<char> span = stackalloc char[2 + (2 * 11)]; // 2 for "..", then for each index 1 for '^' and 10 for longest possible uint
int charsWritten;
int pos = 0;
if (Start.IsFromEnd)
{
span[0] = '^';
pos = 1;
}
bool formatted = ((uint)Start.Value).TryFormat(span.Slice(pos), out charsWritten);
Debug.Assert(formatted);
pos += charsWritten;
span[pos++] = '.';
span[pos++] = '.';
if (End.IsFromEnd)
{
span[pos++] = '^';
}
formatted = ((uint)End.Value).TryFormat(span.Slice(pos), out charsWritten);
Debug.Assert(formatted);
pos += charsWritten;
return new string(span.Slice(0, pos));
}
/// <summary>Create a Range object starting from start index to the end of the collection.</summary>
public static Range StartAt(Index start) => new Range(start, Index.End);
/// <summary>Create a Range object starting from first element in the collection to the end Index.</summary>
public static Range EndAt(Index end) => new Range(Index.Start, end);
/// <summary>Create a Range object starting from first element to the end.</summary>
public static Range All => new Range(Index.Start, Index.End);
/// <summary>Calculate the start offset and length of range object using a collection length.</summary>
/// <param name="length">The length of the collection that the range will be used with. length has to be a positive value.</param>
/// <remarks>
/// For performance reason, we don't validate the input length parameter against negative values.
/// It is expected Range will be used with collections which always have non negative length/count.
/// We validate the range is inside the length scope though.
/// </remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public (int Offset, int Length) GetOffsetAndLength(int length)
{
int start;
Index startIndex = Start;
if (startIndex.IsFromEnd)
start = length - startIndex.Value;
else
start = startIndex.Value;
int end;
Index endIndex = End;
if (endIndex.IsFromEnd)
end = length - endIndex.Value;
else
end = endIndex.Value;
if ((uint)end > (uint)length || (uint)start > (uint)end)
{
ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.length);
}
return (start, end - start);
}
}
}
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