namespace System
{
    using System.Runtime.CompilerServices;
    using System.Runtime.InteropServices;

    [Serializable, StructLayout(LayoutKind.Sequential), TypeDependency("System.Collections.Generic.NullableComparer`1"), TypeDependency("System.Collections.Generic.NullableEqualityComparer`1")]
    public struct Nullable<T> where T: struct
    {
        private bool hasValue;
        internal T value;
        public Nullable(T value)
        {
            this.value = value;
            this.hasValue = true;
        }

        public bool HasValue
        {
            get
            {
                return this.hasValue;
            }
        }
        public T Value
        {
            get
            {
                if (!this.HasValue)
                {
                    ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_NoValue);
                }
                return this.value;
            }
        }
        public T GetValueOrDefault()
        {
            return this.value;
        }

        public T GetValueOrDefault(T defaultValue)
        {
            if (!this.HasValue)
            {
                return defaultValue;
            }
            return this.value;
        }

        public override bool Equals(object other)
        {
            if (!this.HasValue)
            {
                return (other == null);
            }
            if (other == null)
            {
                return false;
            }
            return this.value.Equals(other);
        }

        public override int GetHashCode()
        {
            if (!this.HasValue)
            {
                return 0;
            }
            return this.value.GetHashCode();
        }

        public override string ToString()
        {
            if (!this.HasValue)
            {
                return "";
            }
            return this.value.ToString();
        }

        public static implicit operator T?(T value)
        {
            return new T?(value);
        }

        public static explicit operator T(T? value)
        {
            return value.Value;
        }
    }
}