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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;
namespace System
{
using System.Globalization;
using System.Reflection;
using System.Collections.Generic;
using System.Runtime;
using System.Runtime.CompilerServices;
using System.Security;
using System.Diagnostics.Contracts;
// 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<T>
// can be used where a boxed<T> is use, Nullable<T> can not implement any intefaces
// at all (since T may not). Do NOT add any interfaces to Nullable!
//
[Serializable]
[System.Runtime.Versioning.NonVersionable] // This only applies to field layout
public struct Nullable<T> where T : struct
{
private bool hasValue;
internal T value;
[System.Runtime.Versioning.NonVersionable]
public Nullable(T value) {
this.value = value;
this.hasValue = true;
}
public bool HasValue {
[System.Runtime.Versioning.NonVersionable]
get {
return hasValue;
}
}
public T Value {
get {
if (!hasValue) {
ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_NoValue);
}
return value;
}
}
[System.Runtime.Versioning.NonVersionable]
public T GetValueOrDefault() {
return value;
}
[System.Runtime.Versioning.NonVersionable]
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() : "";
}
[System.Runtime.Versioning.NonVersionable]
public static implicit operator Nullable<T>(T value) {
return new Nullable<T>(value);
}
[System.Runtime.Versioning.NonVersionable]
public static explicit operator T(Nullable<T> value) {
return value.Value;
}
// The following already obsoleted methods were removed:
// public int CompareTo(object other)
// public int CompareTo(Nullable<T> other)
// public bool Equals(Nullable<T> other)
// public static Nullable<T> 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<Nullable<T>>.CompareTo(Nullable<T> other)
// bool IEquatable<Nullable<T>>.Equals(Nullable<T> other)
}
[System.Runtime.InteropServices.ComVisible(true)]
public static class Nullable
{
[System.Runtime.InteropServices.ComVisible(true)]
public static int Compare<T>(Nullable<T> n1, Nullable<T> n2) where T : struct
{
if (n1.HasValue) {
if (n2.HasValue) return Comparer<T>.Default.Compare(n1.value, n2.value);
return 1;
}
if (n2.HasValue) return -1;
return 0;
}
[System.Runtime.InteropServices.ComVisible(true)]
public static bool Equals<T>(Nullable<T> n1, Nullable<T> n2) where T : struct
{
if (n1.HasValue) {
if (n2.HasValue) return EqualityComparer<T>.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((object)nullableType == null) {
throw new ArgumentNullException("nullableType");
}
Contract.EndContractBlock();
Type result = null;
if( nullableType.IsGenericType && !nullableType.IsGenericTypeDefinition) {
// instantiated generic type only
Type genericType = nullableType.GetGenericTypeDefinition();
if( Object.ReferenceEquals(genericType, typeof(Nullable<>))) {
result = nullableType.GetGenericArguments()[0];
}
}
return result;
}
// The following already obsoleted methods were removed:
// public static bool HasValue<T>(Nullable<T> value)
// public static T GetValueOrDefault<T>(Nullable<T> value)
// public static T GetValueOrDefault<T>(Nullable<T> value, T valueWhenNull)
// The following newly obsoleted methods were removed:
// public static Nullable<T> FromObject<T>(object value)
// public static object ToObject<T>(Nullable<T> value)
// public static object Wrap(object value, Type type)
// public static object Unwrap(object value)
}
}
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