Merge pull request #40350 from 333fred/indexrange

Added System.Index and System.Range

src/Compilers/Core/Portable/InternalUtilities/Index.cs

+// 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.Runtime.CompilerServices;
+
+#nullable enable
+
+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, "Non-negative number required.");
+            }
+
+            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, "Non-negative number required.");
+            }
+
+            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, "Non-negative number required.");
+            }
+
+            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)
+        {
+            int 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();
+        }
+    }
+}

src/Compilers/Core/Portable/InternalUtilities/Range.cs

+// 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.Runtime.CompilerServices;
+using Roslyn.Utilities;
+
+#nullable enable
+
+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>
+    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 Hash.Combine(Start.GetHashCode(), End.GetHashCode());
+        }
+
+        /// <summary>Converts the value of the current Range object to its equivalent string representation.</summary>
+        public override string ToString()
+        {
+            return $"{getFromEndSpecifier(Start)}{toString(Start)}..{getFromEndSpecifier(End)}{toString(End)}";
+
+            static string getFromEndSpecifier(Index index) => index.IsFromEnd ? "^" : string.Empty;
+            static string toString(Index index) => ((uint)index.Value).ToString();
+        }
+
+        /// <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)
+            {
+                throw new ArgumentOutOfRangeException(nameof(length));
+            }
+
+            return (start, end - start);
+        }
+    }
+}