是否可以创建构造函数-扩展-方法? 如何创建？

是否可以添加构造函数扩展方法？

示例用例

我想添加一个 List < T > 构造函数，从给定的部分填充缓冲区中接收特定数量的字节(不需要复制相关字节等等的开销) :

...
public static List<T>(this List<T> l, T[] a, int n)
{
for (int i = 0; i < n; i++)
l.Add(a[i]);
}
...

所以用法是:

List<byte> some_list = new List<byte>(my_byte_array,number_of_bytes);

我已经添加了一个 AddRange 扩展方法:

public static void AddRange<T>(this List<T> l, T[] a, int n)
{
for (int i = 0; i < n; i++)
l.Add(a[i]);
}

我也想作为一个构造函数来做。这可能吗? 如果可能-怎么做？

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In a word - no. Take a look at this for some explanation.

They were cut from the C# 3 feature list, then they were cut from the C# 4 feature list, and we can only hope that they could make the C# 5 features, but I'm not very optimistic.

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最佳答案

No, but if you changed your AddRange signature to return the list instance, then you could at least do

var list = new List<int>().AddRange(array, n);

which imho is probably clearer than overloading the constructor anyway.

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SWeko's answer is basically correct, though of course the article he links to is about extension properties rather than extension constructors.

We also did a rough design for extension constructors at the same time as we did extension properties; they would be a nice syntactic sugar for the factory pattern. However, they never got past the design stage; the feature, though nice, is not really necessary and does not enable any awesome new scenarios.

If you have a really awesome problem that extension constructors would solve, I'd be happy to hear more details. The more real-world feedback we get, the better we are able to evaluate the relative merits of the hundreds of different feature suggestions we get every year.

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I know this is a bump, just wanted to point out you can inherit the List class and do something like this:

class List<T> : System.Collections.Generic.List<T>
{
public List(T[] a, int n)
: base()
{
AddRange(a, n);
}
}
小开

Yes-ish but no?

MyClass{
public MyClass(params){ //do stuff };
public MyClass MyConstructorAddOn(moreParams){ //do more stuff; return this;}
}

then call this way:

MyClass(params).MyConstructorAddOn(moreParams);

It works a bit like an extension method. Although NOT a constructor, it can be used as a daisy chain on a constructor to do more stuff outside of the constructor immediately. I believe this is called fluent interfaces.


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