Code:
/ DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / Nullable.cs / 1 / Nullable.cs
// ==++== // // Copyright (c) Microsoft Corporation. All rights reserved. // // ==--== using System; namespace System { using System.Globalization; using System.Reflection; using System.Collections.Generic; using System.Runtime.CompilerServices; using System.Security; // Warning, don't put System.Runtime.Serialization.On*Serializ*Attribute // on this class without first fixing ObjectClone::InvokeVtsCallbacks // Also, because we have special type system support that says a a boxed Nullable// can be used where a boxed is use, Nullable can not implement any intefaces // at all (since T may not). Do NOT add any interfaces to Nullable! // [TypeDependencyAttribute("System.Collections.Generic.NullableComparer`1")] [TypeDependencyAttribute("System.Collections.Generic.NullableEqualityComparer`1")] [Serializable()] public struct Nullable where T : struct { private bool hasValue; internal T value; public Nullable(T value) { this.value = value; this.hasValue = true; } public bool HasValue { get { return hasValue; } } public T Value { get { if (!HasValue) { ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_NoValue); } return value; } } public T GetValueOrDefault() { return value; } public T GetValueOrDefault(T defaultValue) { return HasValue ? value : defaultValue; } public override bool Equals(object other) { if (!HasValue) return other == null; if (other == null) return false; return value.Equals(other); } public override int GetHashCode() { return HasValue ? value.GetHashCode() : 0; } public override string ToString() { return HasValue ? value.ToString() : ""; } public static implicit operator Nullable (T value) { return new Nullable (value); } public static explicit operator T(Nullable value) { return value.Value; } // The following already obsoleted methods were removed: // public int CompareTo(object other) // public int CompareTo(Nullable other) // public bool Equals(Nullable other) // public static Nullable FromObject(object value) // public object ToObject() // public string ToString(string format) // public string ToString(IFormatProvider provider) // public string ToString(string format, IFormatProvider provider) // The following newly obsoleted methods were removed: // string IFormattable.ToString(string format, IFormatProvider provider) // int IComparable.CompareTo(object other) // int IComparable >.CompareTo(Nullable other) // bool IEquatable >.Equals(Nullable other) } [System.Runtime.InteropServices.ComVisible(true)] public static class Nullable { [System.Runtime.InteropServices.ComVisible(true)] public static int Compare (Nullable n1, Nullable n2) where T : struct { if (n1.HasValue) { if (n2.HasValue) return Comparer .Default.Compare(n1.value, n2.value); return 1; } if (n2.HasValue) return -1; return 0; } [System.Runtime.InteropServices.ComVisible(true)] public static bool Equals (Nullable n1, Nullable n2) where T : struct { if (n1.HasValue) { if (n2.HasValue) return EqualityComparer .Default.Equals(n1.value, n2.value); return false; } if (n2.HasValue) return false; return true; } // If the type provided is not a Nullable Type, return null. // Otherwise, returns the underlying type of the Nullable type public static Type GetUnderlyingType(Type nullableType) { if( nullableType == null) { throw new ArgumentNullException("nullableType"); } Type result = null; if( nullableType.IsGenericType && !nullableType.IsGenericTypeDefinition) { // instantiated generic type only Type genericType = nullableType.GetGenericTypeDefinition(); if( genericType == typeof(Nullable<>)) { result = nullableType.GetGenericArguments()[0]; } } return result; } // The following already obsoleted methods were removed: // public static bool HasValue (Nullable value) // public static T GetValueOrDefault (Nullable value) // public static T GetValueOrDefault (Nullable value, T valueWhenNull) // The following newly obsoleted methods were removed: // public static Nullable FromObject (object value) // public static object ToObject (Nullable value) // public static object Wrap(object value, Type type) // public static object Unwrap(object value) } }
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