apewer-dotnet/Apewer/Class.cs

using System;

/// <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 Class&lt;T&gt; 到 Boolean 的隐式转换，判断 Class&lt;T&gt; 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 Class&lt;T&gt; 到 T 的隐式转换。</summary>
    // public static implicit operator T(Class<T> instance) => instance == null ? default : instance.Value;

    // /// <summary>从 T 到 Class&lt;T&gt; 的隐式转换。</summary>
    // public static implicit operator Class<T>(T value) => new Class<T>(value);

    #endregion

}