Question

我想写一个会创建另一个类的不可变副本的类，而我这样做的方式要求副本在构造函数中获取日期和原始实例。我知道你不能创建一个指定参数的构造函数约束，但有没有办法使用代码契约解决它？

public class Copier<o, c>
    where o : class, INotifyPropertyChanged
    where c : class, c // ideally new(datetime, o)
{
    private Dictionary<DateTime, c> copies;

    public Copier(o original)
    {
        this.copies = new Dictionary<DateTime, c>();
        original.PropertyChanged += 
            this.propertyChangedHandler(object sender, PropertyChangedEventArgs args);
    }

    private void propertyChangedHandler(object sender, PropertyChangedEventArgs args)
    {
        var original = sender as o;
        var now = DateTime.Now;
        this.copies.Add(now, new c(now, original)); // error here
    }
}

复制clases是由我创建的，从原件继承，覆盖所有属性为readonly并从构造函数中复制原始值。

注意：有一项要求（由我强加）无法修改原始对象。

Answer 1

根据建议，传递创建委托：

public class Copier<o, c>
    where o : class, INotifyPropertyChanged
    where c : class, c // ideally new(datetime, o)
{
private Dictionary<DateTime, c> copies;
private Func<o, DateTime, c> copyFunc;

public Copier(o original, Func<o, DateTime, c> copyFunc)
{
    this.copyFunc = copyFunc;
    this.copies = new Dictionary<DateTime, c>();
    original.PropertyChanged += 
        this.propertyChangedHandler(object sender, PropertyChangedEventArgs args);
}

private void propertyChangedHandler(object sender, PropertyChangedEventArgs args)
{
    var original = sender as o;
    var now = DateTime.Now;
    this.copies.Add(copyFunc(now, original)); 
}

}

我可以使用代码契约来解决无法具有泛型构造函数约束的问题吗？

1 个答案: