apewer-dotnet/Apewer/Class.cs

using System;

namespace Apewer
{

    /// <summary>装箱类。</summary>
    public sealed class Class<T> : IComparable, IComparable<T>, IComparable<Class<T>>
    {

        private bool _hashcode = false;
        private bool _equals = false;

        /// <summary>装箱对象。</summary>
        public T Value { get; set; }

        /// <summary></summary>
        public bool IsNull { get { return Value == null; } }

        /// <summary></summary>
        public bool HasValue { get { return Value != null; } }

        /// <summary>创建默认值。</summary>
        public Class(T value = default, bool tryEquals = true, bool tryHashCode = true)
        {
            Value = value;
            _hashcode = tryHashCode;
            _equals = tryEquals;
        }

        #region Override

        /// <summary></summary>
        public override int GetHashCode()
        {
            if (_hashcode && Value != null)
            {
                return Value.GetHashCode();
            }
            return base.GetHashCode();
        }

        /// <summary></summary>
        public override bool Equals(object obj)
        {
            if (_equals)
            {
                var right = obj as Class<T>;
                if (right == null) return false;

                if (Value == null && right.Value == null) return true;
                if (Value == null && right.Value != null) return false;
                if (Value != null && right.Value == null) return false;
                return Value.Equals(right.Value);
            }
            return base.Equals(obj);
        }

        /// <summary></summary>
        public override string ToString()
        {
            if (Value == null) return "";
            return Value.ToString();
        }

        #endregion

        #region IComparable

        /// <summary></summary>
        /// <exception cref="MissingMemberException"></exception>
        /// <exception cref="NotSupportedException"></exception>
        public int CompareTo(object obj)
        {
            if (obj != null && obj is T) return CompareTo((T)obj);
            if (obj != null && obj is Class<T>) return CompareTo(obj as Class<T>);

            if (Value == null) throw new MissingMemberException(typeof(T).FullName, nameof(Value));
            if (!(Value is IComparable)) throw new NotSupportedException();
            return ((IComparable)Value).CompareTo(obj);
        }

        /// <summary></summary>
        /// <exception cref="MissingMemberException"></exception>
        /// <exception cref="NotSupportedException"></exception>
        public int CompareTo(T other)
        {
            if (Value == null) throw new MissingMemberException(typeof(T).FullName, nameof(Value));
            if (!(Value is IComparable)) throw new NotSupportedException();
            return ((IComparable<T>)Value).CompareTo(other);
        }

        /// <summary></summary>
        /// <exception cref="MissingMemberException"></exception>
        /// <exception cref="NotSupportedException"></exception>
        public int CompareTo(Class<T> other)
        {
            if (Value == null) throw new MissingMemberException(typeof(T).FullName, nameof(Value));
            if (other == null || !other.HasValue) return 1;

            if (Value is IComparable) return ((IComparable)Value).CompareTo(other.Value);
            if (Value is IComparable<T>) return ((IComparable<T>)Value).CompareTo(other.Value);

            throw new NotSupportedException();
        }

        #endregion

        #region 运算符。

        /// <summary>从 <see cref="Class{T}"/> 到 Boolean 的隐式转换，判断 <see cref="Class{T}"/> 包含值。</summary>
        /// <remarks>当 T 是 Boolean 时，获取 Value。<br />当 T 是 String 时，判断 Value 不为 NULL 且不为空。</remarks>
        public static implicit operator bool(Class<T> instance)
        {
            if (instance == null) return false;

            var boolean = instance as Class<bool>;
            if (boolean != null) return boolean.Value;

            var text = instance as Class<string>;
            if (text != null) return !string.IsNullOrEmpty(text.Value);

            return instance.HasValue;
        }

        /// <summary>从 <see cref="Class{T}"/> 到 T 的隐式转换。</summary>
        public static implicit operator T(Class<T> instance)
        {
            if (instance == null) return default(T);

            if (typeof(T).Equals(typeof(bool))) return instance.Value;
            return instance.Value;
        }

        /// <summary>从 T 到 <see cref="Class{T}"/> 的隐式转换。</summary>
        public static implicit operator Class<T>(T value) => new Class<T>(value);

        #endregion

    }

}