这个不可变结构应该是一个可变类吗？

Question

我向同事程序员展示了这个结构,他们认为它应该是一个可变类.他们觉得没有空引用和根据需要改变对象的能力是不方便的.我真的想知道是否有任何其他原因使这个变成一个可变类.

[Serializable]
public struct PhoneNumber : IEquatable<PhoneNumber>
{
    private const int AreaCodeShift = 54;
    private const int CentralOfficeCodeShift = 44;
    private const int SubscriberNumberShift = 30;
    private const int CentralOfficeCodeMask = 0x000003FF;
    private const int SubscriberNumberMask = 0x00003FFF;
    private const int ExtensionMask = 0x3FFFFFFF;


    private readonly ulong value;


    public int AreaCode
    {
        get { return UnmaskAreaCode(value); }
    }

    public int CentralOfficeCode
    {
        get { return UnmaskCentralOfficeCode(value); }
    }

    public int SubscriberNumber
    {
        get { return UnmaskSubscriberNumber(value); }
    }

    public int Extension
    {
        get { return UnmaskExtension(value); }
    }


    public PhoneNumber(ulong value)
        : this(UnmaskAreaCode(value), UnmaskCentralOfficeCode(value), UnmaskSubscriberNumber(value), UnmaskExtension(value), true)
    {

    }

    public PhoneNumber(int areaCode, int centralOfficeCode, int subscriberNumber)
        : this(areaCode, centralOfficeCode, subscriberNumber, 0, true)
    {

    }

    public PhoneNumber(int areaCode, int centralOfficeCode, int subscriberNumber, int extension)
        : this(areaCode, centralOfficeCode, subscriberNumber, extension, true)
    {

    }

    private PhoneNumber(int areaCode, int centralOfficeCode, int subscriberNumber, int extension, bool throwException)
    {
        value = 0;

        if (areaCode < 200 || areaCode > 989)
        {
            if (!throwException) return;
            throw new ArgumentOutOfRangeException("areaCode", areaCode, @"The area code portion must fall between 200 and 989.");
        }
        else if (centralOfficeCode < 200 || centralOfficeCode > 999)
        {
            if (!throwException) return;
            throw new ArgumentOutOfRangeException("centralOfficeCode", centralOfficeCode, @"The central office code portion must fall between 200 and 999.");
        }
        else if (subscriberNumber < 0 || subscriberNumber > 9999)
        {
            if (!throwException) return;
            throw new ArgumentOutOfRangeException("subscriberNumber", subscriberNumber, @"The subscriber number portion must fall between 0 and 9999.");
        }
        else if (extension < 0 || extension > 1073741824)
        {
            if (!throwException) return;
            throw new ArgumentOutOfRangeException("extension", extension, @"The extension portion must fall between 0 and 1073741824.");
        }
        else if (areaCode.ToString()[1] == '9')
        {
            if (!throwException) return;
            throw new ArgumentOutOfRangeException("areaCode", areaCode, @"The second digit of the area code cannot be greater than 8.");
        }
        else
        {
            value |= ((ulong)(uint)areaCode << AreaCodeShift);
            value |= ((ulong)(uint)centralOfficeCode << CentralOfficeCodeShift);
            value |= ((ulong)(uint)subscriberNumber << SubscriberNumberShift);
            value |= ((ulong)(uint)extension);
        }
    }


    public override bool Equals(object obj)
    {
        return obj != null && obj.GetType() == typeof(PhoneNumber) && Equals((PhoneNumber)obj);
    }

    public bool Equals(PhoneNumber other)
    {
        return this.value == other.value;
    }

    public override int GetHashCode()
    {
        return value.GetHashCode();
    }

    public override string ToString()
    {
        return ToString(PhoneNumberFormat.Separated);
    }

    public string ToString(PhoneNumberFormat format)
    {
        switch (format)
        {
            case PhoneNumberFormat.Plain:
                return string.Format(@"{0:D3}{1:D3}{2:D4}{3:#}", AreaCode, CentralOfficeCode, SubscriberNumber, Extension).Trim();
            case PhoneNumberFormat.Separated:
                return string.Format(@"{0:D3}-{1:D3}-{2:D4} {3:#}", AreaCode, CentralOfficeCode, SubscriberNumber, Extension).Trim();
            default:
                throw new ArgumentOutOfRangeException("format");
        }
    }

    public ulong ToUInt64()
    {
        return value;
    }


    public static PhoneNumber Parse(string value)
    {
        var result = default(PhoneNumber);
        if (!TryParse(value, out result))
        {
            throw new FormatException(string.Format(@"The string ""{0}"" could not be parsed as a phone number.", value));
        }
        return result;
    }

    public static bool TryParse(string value, out PhoneNumber result)
    {
        result = default(PhoneNumber);

        if (string.IsNullOrEmpty(value))
        {
            return false;
        }

        var index = 0;
        var numericPieces = new char[value.Length];

        foreach (var c in value)
        {
            if (char.IsNumber(c))
            {
                numericPieces[index++] = c;
            }
        }

        if (index < 9)
        {
            return false;
        }

        var numericString = new string(numericPieces);
        var areaCode = int.Parse(numericString.Substring(0, 3));
        var centralOfficeCode = int.Parse(numericString.Substring(3, 3));
        var subscriberNumber = int.Parse(numericString.Substring(6, 4));
        var extension = 0;

        if (numericString.Length > 10)
        {
            extension = int.Parse(numericString.Substring(10));
        }

        result = new PhoneNumber(
            areaCode,
            centralOfficeCode,
            subscriberNumber,
            extension,
            false
        );

        return result.value != 0;
    }

    public static bool operator ==(PhoneNumber left, PhoneNumber right)
    {
        return left.Equals(right);
    }

    public static bool operator !=(PhoneNumber left, PhoneNumber right)
    {
        return !left.Equals(right);
    }

    private static int UnmaskAreaCode(ulong value)
    {
        return (int)(value >> AreaCodeShift);
    }

    private static int UnmaskCentralOfficeCode(ulong value)
    {
        return (int)((value >> CentralOfficeCodeShift) & CentralOfficeCodeMask);
    }

    private static int UnmaskSubscriberNumber(ulong value)
    {
        return (int)((value >> SubscriberNumberShift) & SubscriberNumberMask);
    }

    private static int UnmaskExtension(ulong value)
    {
        return (int)(value & ExtensionMask);
    }
}

public enum PhoneNumberFormat
{
    Plain,
    Separated
}

Answer 1

操纵电话号码的程序是过程的模型.

因此,在进程中使不可变的东西在代码中不可变.在过程中使可变的东西在代码中变得可变.

例如,一个过程可能包括一个人.一个人有一个名字.一个人可以在保留自己身份的同时更改姓名.因此,person对象的名称应该是可变的.

一个人有一个电话号码.一个人可以在保留身份的同时更改他们的电话号码.因此,一个人的电话号码应该是可变的.

电话号码具有区号.电话号码不能更改其区号并保留其身份; 您更改区号,现在有一个不同的电话号码.因此,电话号码的区号应该是不可变的.

Answer 2

我认为保持它是一个不可变的结构是很好的 - 但我个人只是为每个逻辑字段使用单独的变量,除非你一次在内存中有大量的这些变量.如果您坚持使用最合适的类型(例如ushort3-4位数),那么它应该不会那么昂贵 - 并且代码将更加清晰.