Nullable.cs source code in C# .NET

                        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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