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@meziantou meziantou/Range.cs
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C# 8: Index and Range
// https://github.com/dotnet/corefx/blob/1597b894a2e9cac668ce6e484506eca778a85197/src/Common/src/CoreLib/System/Index.cs
// https://github.com/dotnet/corefx/blob/1597b894a2e9cac668ce6e484506eca778a85197/src/Common/src/CoreLib/System/Range.cs
using System.Runtime.CompilerServices;
namespace System
{
/// <summary>Represent a type can be used to index a collection either from the start or the end.</summary>
/// <remarks>
/// Index is used by the C# compiler to support the new index syntax
/// <code>
/// int[] someArray = new int[5] { 1, 2, 3, 4, 5 } ;
/// int lastElement = someArray[^1]; // lastElement = 5
/// </code>
/// </remarks>
internal readonly struct Index : IEquatable<Index>
{
private readonly int _value;
/// <summary>Construct an Index using a value and indicating if the index is from the start or from the end.</summary>
/// <param name="value">The index value. it has to be zero or positive number.</param>
/// <param name="fromEnd">Indicating if the index is from the start or from the end.</param>
/// <remarks>
/// If the Index constructed from the end, index value 1 means pointing at the last element and index value 0 means pointing at beyond last element.
/// </remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Index(int value, bool fromEnd = false)
{
if (value < 0)
{
throw new ArgumentOutOfRangeException(nameof(value), "value must be non-negative");
}
if (fromEnd)
_value = ~value;
else
_value = value;
}
// The following private constructors mainly created for perf reason to avoid the checks
private Index(int value)
{
_value = value;
}
/// <summary>Create an Index pointing at first element.</summary>
public static Index Start => new Index(0);
/// <summary>Create an Index pointing at beyond last element.</summary>
public static Index End => new Index(~0);
/// <summary>Create an Index from the start at the position indicated by the value.</summary>
/// <param name="value">The index value from the start.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static Index FromStart(int value)
{
if (value < 0)
{
throw new ArgumentOutOfRangeException(nameof(value), "value must be non-negative");
}
return new Index(value);
}
/// <summary>Create an Index from the end at the position indicated by the value.</summary>
/// <param name="value">The index value from the end.</param>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static Index FromEnd(int value)
{
if (value < 0)
{
throw new ArgumentOutOfRangeException(nameof(value), "value must be non-negative");
}
return new Index(~value);
}
/// <summary>Returns the index value.</summary>
public int Value
{
get
{
if (_value < 0)
{
return ~_value;
}
else
{
return _value;
}
}
}
/// <summary>Indicates whether the index is from the start or the end.</summary>
public bool IsFromEnd => _value < 0;
/// <summary>Calculate the offset from the start using the giving collection length.</summary>
/// <param name="length">The length of the collection that the Index will be used with. length has to be a positive value</param>
/// <remarks>
/// For performance reason, we don't validate the input length parameter and the returned offset value against negative values.
/// we don't validate either the returned offset is greater than the input length.
/// It is expected Index will be used with collections which always have non negative length/count. If the returned offset is negative and
/// then used to index a collection will get out of range exception which will be same affect as the validation.
/// </remarks>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public int GetOffset(int length)
{
var offset = _value;
if (IsFromEnd)
{
// offset = length - (~value)
// offset = length + (~(~value) + 1)
// offset = length + value + 1
offset += length + 1;
}
return offset;
}
/// <summary>Indicates whether the current Index 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) => value is Index && _value == ((Index)value)._value;
/// <summary>Indicates whether the current Index object is equal to another Index object.</summary>
/// <param name="other">An object to compare with this object</param>
public bool Equals(Index other) => _value == other._value;
/// <summary>Returns the hash code for this instance.</summary>
public override int GetHashCode() => _value;
/// <summary>Converts integer number to an Index.</summary>
public static implicit operator Index(int value) => FromStart(value);
/// <summary>Converts the value of the current Index object to its equivalent string representation.</summary>
public override string ToString()
{
if (IsFromEnd)
return "^" + ((uint)Value).ToString();
return ((uint)Value).ToString();
}
}
/// <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>
internal 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) =>
value is Range r &&
r.Start.Equals(Start) &&
r.End.Equals(End);
/// <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 Start.GetHashCode() * 31 + End.GetHashCode();
}
/// <summary>Converts the value of the current Range object to its equivalent string representation.</summary>
public override string ToString()
{
return Start + ".." + End;
}
/// <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;
var startIndex = Start;
if (startIndex.IsFromEnd)
start = length - startIndex.Value;
else
start = startIndex.Value;
int end;
var endIndex = End;
if (endIndex.IsFromEnd)
end = length - endIndex.Value;
else
end = endIndex.Value;
if ((uint)end > (uint)length || (uint)start > (uint)end)
{
throw new ArgumentOutOfRangeException(nameof(length));
}
return (start, end - start);
}
}
}
namespace System.Runtime.CompilerServices
{
internal static class RuntimeHelpers
{
/// <summary>
/// Slices the specified array using the specified range.
/// </summary>
public static T[] GetSubArray<T>(T[] array, Range range)
{
if (array == null)
{
throw new ArgumentNullException(nameof(array));
}
(int offset, int length) = range.GetOffsetAndLength(array.Length);
if (default(T) != null || typeof(T[]) == array.GetType())
{
// We know the type of the array to be exactly T[].
if (length == 0)
{
return Array.Empty<T>();
}
var dest = new T[length];
Array.Copy(array, offset, dest, 0, length);
return dest;
}
else
{
// The array is actually a U[] where U:T.
var dest = (T[])Array.CreateInstance(array.GetType().GetElementType(), length);
Array.Copy(array, offset, dest, 0, length);
return dest;
}
}
}
}
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