c# - 在 C# : PostSharp or T4 templates? 中生成不可变值对象

Question

我厌倦了样板式不可变值对象代码。 PostSharp 或 T4 模板是否允许我进行以下转换？

输入:

public struct Name
{
    public string FirstName;
    public string LastName;
}

输出:

public struct Name : IEquatable<Name>
{
    private readonly string firstName;
    private readonly string lastName;

    public string FirstName { get { return this.firstName; } }
    public string LastName { get { return this.lastName; } }

    public Name(string firstName, string lastName)
    {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public bool Equals(Name other)
    {
        return this.FirstName == other.FirstName && this.LastName == other.LastName;
    }
    public override bool Equals(object obj)
    {
        return obj is Name && this.Equals((Name)obj);
    }
    public override int GetHashCode()
    {
        unchecked
        {
            int hash = 17;
            if (this.FirstName != null)
            {
                hash = hash * 29 + this.FirstName.GetHashCode();
            }
            if (this.LastName != null)
            {
                hash = hash * 29 + this.LastName.GetHashCode();
            }
            return hash;
        }
    }

    public static bool operator==(Name a, Name b)
    {
        return a.Equals(b);
    }
    public static bool operator !=(Name a, Name b)
    {
        return !(a == b);
    }
}

显然 PostSharp 需要一个 [MakeImmutable] 注释，这很好。我想要根据原始类型生成 class 或 struct 的选项。另请注意，GetHashCode 必须省略对值类型成员的 null 检查。

我相当确定这两种技术都具有这种能力，但我自己只是 PostSharp 方面/T4 模板的使用者，我不知道哪种技术更好或更容易完成这项任务。无论您给出哪个答案，我都会花一两天的时间学习足够的知识来完成这项工作:)。

Answer 1

我做了一些东西来满足你最近的要求(使用 T4 模板)，所以这是绝对可能的:

https://github.com/xaviergonz/T4Immutable

例如，给定这个:

[ImmutableClass(Options = ImmutableClassOptions.IncludeOperatorEquals)]
class Person {
  private const int AgeDefaultValue = 18;

  public string FirstName { get; }
  public string LastName { get; }
  public int Age { get; }

  [ComputedProperty]
  public string FullName {
    get {
      return FirstName + " " + LastName;
    }
  }
}

它会在单独的部分类文件中自动为您生成以下内容:

• 一个构造函数，例如 public Person(string firstName, stringlastName, int age = 18) 将初始化值。
• Equals(object other) 和 Equals(Person other) 的有效实现。它还会为您添加 IEquatable 接口(interface)。在职的operator== 和 operator!= 的实现
• GetHashCode() 的有效实现更好的 ToString() 输出如“Person { FirstName=John, LastName=Doe, Age=21 }”
• Person With(...) 方法，可用于生成具有 0 个或多个属性更改的新不可变克隆(例如 var janeDoe = johnDoe.With(firstName: "Jane", age: 20)

所以它会生成这个(排除一些冗余属性):

using System;

partial class Person : IEquatable<Person> {
  public Person(string firstName, string lastName, int age = 18) {
    this.FirstName = firstName;
    this.LastName = lastName;
    this.Age = age;
    _ImmutableHashCode = new { this.FirstName, this.LastName, this.Age }.GetHashCode();
  }

  private bool ImmutableEquals(Person obj) {
    if (ReferenceEquals(this, obj)) return true;
    if (ReferenceEquals(obj, null)) return false;
    return T4Immutable.Helpers.AreEqual(this.FirstName, obj.FirstName) && T4Immutable.Helpers.AreEqual(this.LastName, obj.LastName) && T4Immutable.Helpers.AreEqual(this.Age, obj.Age);
  }

  public override bool Equals(object obj) {
    return ImmutableEquals(obj as Person);
  }

  public bool Equals(Person obj) {
    return ImmutableEquals(obj);
  }

  public static bool operator ==(Person a, Person b) {
    return T4Immutable.Helpers.AreEqual(a, b);
  }

  public static bool operator !=(Person a, Person b) {
    return !T4Immutable.Helpers.AreEqual(a, b);
  }

  private readonly int _ImmutableHashCode;

  private int ImmutableGetHashCode() {
    return _ImmutableHashCode;
  }

  public override int GetHashCode() {
    return ImmutableGetHashCode();
  }

  private string ImmutableToString() {
    var sb = new System.Text.StringBuilder();
    sb.Append(nameof(Person) + " { ");

    var values = new string[] {
      nameof(this.FirstName) + "=" + T4Immutable.Helpers.ToString(this.FirstName),
      nameof(this.LastName) + "=" + T4Immutable.Helpers.ToString(this.LastName),
      nameof(this.Age) + "=" + T4Immutable.Helpers.ToString(this.Age),
    };

    sb.Append(string.Join(", ", values) + " }");
    return sb.ToString();
  }

  public override string ToString() {
    return ImmutableToString();
  }

  private Person ImmutableWith(T4Immutable.WithParam<string> firstName = default(T4Immutable.WithParam<string>), T4Immutable.WithParam<string> lastName = default(T4Immutable.WithParam<string>), T4Immutable.WithParam<int> age = default(T4Immutable.WithParam<int>)) {
    return new Person(
      !firstName.HasValue ? this.FirstName : firstName.Value,
      !lastName.HasValue ? this.LastName : lastName.Value,
      !age.HasValue ? this.Age : age.Value
    );
  }

  public Person With(T4Immutable.WithParam<string> firstName = default(T4Immutable.WithParam<string>), T4Immutable.WithParam<string> lastName = default(T4Immutable.WithParam<string>), T4Immutable.WithParam<int> age = default(T4Immutable.WithParam<int>)) {
    return ImmutableWith(firstName, lastName, age);
  }

}

项目页面中还介绍了一些其他功能。