219 lines
8.5 KiB
C#
219 lines
8.5 KiB
C#
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using System;
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using System.Globalization;
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////TODO: goal should be to end up with this being internal
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////TODO: instead of using string.Intern, put them in a custom table and allow passing them around as indices
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//// (this will probably also be useful for jobs)
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//// when this is implemented, also allow interning directly from Substrings
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namespace UnityEngine.InputSystem.Utilities
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{
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/// <summary>
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/// Wraps around a string to allow for faster case-insensitive string comparisons while
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/// preserving original casing.
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/// </summary>
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/// <remarks>
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/// Unlike <c>string</c>, InternedStrings can be compared with a quick <c>Object.ReferenceEquals</c>
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/// comparison and without actually comparing string contents.
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///
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/// Also, unlike <c>string</c>, the representation of an empty and a <c>null</c> string is identical.
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///
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/// Note that all string comparisons using InternedStrings are both case-insensitive and culture-insensitive.
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///
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/// There is a non-zero cost to creating an InternedString. The first time a new unique InternedString
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/// is encountered, there may also be a GC heap allocation.
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/// </remarks>
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public struct InternedString : IEquatable<InternedString>, IComparable<InternedString>
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{
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private readonly string m_StringOriginalCase;
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private readonly string m_StringLowerCase;
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/// <summary>
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/// Length of the string in characters. Equivalent to <c>string.Length</c>.
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/// </summary>
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/// <value>Length of the string.</value>
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public int length => m_StringLowerCase?.Length ?? 0;
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/// <summary>
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/// Initialize the InternedString with the given string. Except if the string is <c>null</c>
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/// or empty, this requires an internal lookup (this is the reason the conversion from <c>string</c>
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/// to InternedString is not implicit).
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/// </summary>
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/// <param name="text">A string. Can be null.</param>
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/// <remarks>
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/// The InternedString preserves the original casing. Meaning that <see cref="ToString()"/> will
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/// return the string as it was supplied through <paramref name="text"/>. However, comparison
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/// between two InternedStrings is still always just a reference comparisons regardless of case
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/// and culture.
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///
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/// <example>
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/// <code>
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/// var lowerCase = new InternedString("text");
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/// var upperCase = new InternedString("TEXT");
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///
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/// // This is still just a quick reference comparison:
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/// if (lowerCase == upperCase)
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/// Debug.Log("True");
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///
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/// // But this prints the strings in their original casing.
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/// Debug.Log(lowerCase);
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/// Debug.Log(upperCase);
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/// </code>
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/// </example>
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/// </remarks>
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public InternedString(string text)
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{
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if (string.IsNullOrEmpty(text))
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{
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m_StringOriginalCase = null;
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m_StringLowerCase = null;
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}
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else
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{
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////TODO: I think instead of string.Intern() this should use a custom weak-referenced intern table
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//// (this way we can also avoid the garbage from ToLower())
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m_StringOriginalCase = string.Intern(text);
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m_StringLowerCase = string.Intern(text.ToLower(CultureInfo.InvariantCulture));
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}
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}
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/// <summary>
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/// Whether the string is empty, i.e. has a <see cref="length"/> of zero. If so, the
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/// InternedString corresponds to <c>default(InternedString)</c>.
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/// </summary>
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/// <returns>True if the string is empty.</returns>
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public bool IsEmpty()
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{
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return m_StringLowerCase == null;
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}
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/// <summary>
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/// Return a lower-case version of the string.
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/// </summary>
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/// <returns>A lower-case version of the string.</returns>
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/// <remarks>
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/// InternedStrings internally always store a lower-case version which means that this
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/// method does not incur a GC heap allocation cost.
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/// </remarks>
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public string ToLower()
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{
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return m_StringLowerCase;
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}
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/// <summary>
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/// Compare the InternedString to given object.
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/// </summary>
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/// <param name="obj">An object. If it is a <c>string</c>, performs a string comparison. If
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/// it is an InternedString, performs an InternedString-comparison. Otherwise returns false.</param>
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/// <returns>True if the InternedString is equal to <paramref name="obj"/>.</returns>
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public override bool Equals(object obj)
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{
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if (obj is InternedString other)
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return Equals(other);
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if (obj is string str)
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{
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if (m_StringLowerCase == null)
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return string.IsNullOrEmpty(str);
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return string.Equals(m_StringLowerCase, str.ToLower(CultureInfo.InvariantCulture));
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}
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return false;
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}
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/// <summary>
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/// Compare two InternedStrings for equality. They are equal if, ignoring case and culture,
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/// their text is equal.
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/// </summary>
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/// <param name="other">Another InternedString.</param>
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/// <returns>True if the two InternedStrings are equal.</returns>
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/// <remarks>
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/// This operation is cheap and does not involve an actual string comparison. Instead,
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/// a simple <c>Object.ReferenceEquals</c> comparison is performed.
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/// </remarks>
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public bool Equals(InternedString other)
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{
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return ReferenceEquals(m_StringLowerCase, other.m_StringLowerCase);
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}
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public int CompareTo(InternedString other)
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{
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return string.Compare(m_StringLowerCase, other.m_StringLowerCase,
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StringComparison.InvariantCultureIgnoreCase);
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}
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/// <summary>
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/// Compute a hash code for the string. Equivalent to <c>string.GetHashCode</c>.
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/// </summary>
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/// <returns>A hash code.</returns>
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public override int GetHashCode()
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{
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if (m_StringLowerCase == null)
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return 0;
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return m_StringLowerCase.GetHashCode();
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}
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public override string ToString()
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{
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return m_StringOriginalCase ?? string.Empty;
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}
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public static bool operator==(InternedString a, InternedString b)
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{
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return a.Equals(b);
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}
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public static bool operator!=(InternedString a, InternedString b)
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{
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return !a.Equals(b);
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}
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public static bool operator==(InternedString a, string b)
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{
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return string.Compare(a.m_StringLowerCase, b.ToLower(CultureInfo.InvariantCulture),
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StringComparison.InvariantCultureIgnoreCase) == 0;
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}
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public static bool operator!=(InternedString a, string b)
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{
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return string.Compare(a.m_StringLowerCase, b.ToLower(CultureInfo.InvariantCulture),
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StringComparison.InvariantCultureIgnoreCase) != 0;
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}
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public static bool operator==(string a, InternedString b)
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{
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return string.Compare(a.ToLower(CultureInfo.InvariantCulture), b.m_StringLowerCase,
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StringComparison.InvariantCultureIgnoreCase) == 0;
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}
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public static bool operator!=(string a, InternedString b)
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{
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return string.Compare(a.ToLower(CultureInfo.InvariantCulture), b.m_StringLowerCase,
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StringComparison.InvariantCultureIgnoreCase) != 0;
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}
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public static bool operator<(InternedString left, InternedString right)
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{
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return string.Compare(left.m_StringLowerCase, right.m_StringLowerCase,
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StringComparison.InvariantCultureIgnoreCase) < 0;
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}
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public static bool operator>(InternedString left, InternedString right)
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{
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return string.Compare(left.m_StringLowerCase, right.m_StringLowerCase,
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StringComparison.InvariantCultureIgnoreCase) > 0;
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}
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/// <summary>
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/// Convert the given InternedString back to a <c>string</c>. Equivalent to <see cref="ToString()"/>.
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/// </summary>
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/// <param name="str">An InternedString.</param>
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/// <returns>A string.</returns>
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public static implicit operator string(InternedString str)
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{
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return str.ToString();
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}
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}
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}
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