C＃成员变量初始化;最佳实践？ [英] C# member variable initialization; best practice?

问题描述

是更好来初始化声明类成员变量

Is it better to initialize class member variables on declaration

private List<Thing> _things = new List<Thing>();
private int _arb = 99;

或默认的构造函数？

private List<Thing> _things;
private int _arb;

public TheClass()
{
  _things = new List<Thing>();
  _arb = 99;
}

这纯粹是一种风格问题还是有性能折衷，一种方式或其他？

Is it simply a matter of style or are there performance trade-offs, one way or the other?

推荐答案

在性能方面，没有真正的区别;字段初始被实现为构造逻辑。唯一的区别是，字段初始发生之前任何基地/本构造函数。

In terms of performance, there is no real difference; field initializers are implemented as constructor logic. The only difference is that field initializers happen before any "base"/"this" constructor.

构造方法可以自动实现属性可以使用（字段初始不能） - 即

The constructor approach can be used with auto-implemented properties (field initializers cannot) - i.e.

[DefaultValue("")]
public string Foo {get;set;}
public Bar() { // ctor
  Foo = "";
}

除此之外，我倾向于preFER领域的初始化程序语法;我发现它让事情本地化 - 即

Other than that, I tend to prefer the field initializer syntax; I find it keeps things localized - i.e.

private readonly List<SomeClass> items = new List<SomeClass>();
public List<SomeClass> Items {get {return items;}}

我没有去打猎向上和向下找到它被分配...

I don't have to go hunting up and down to find where it is assigned...

最明显的例外是您需要执行复杂的逻辑或处理构造函数的参数 - 在这种情况下，基于构造函数初始化是要走的路。同样，如果你有多个构造函数，这将是preferable的领域总是设置相同的方式 - 所以你可能有这样构造函数：

The obvious exception is where you need to perform complex logic or deal with constructor parameters - in which case constructor-based initialization is the way to go. Likewise, if you have multiple constructors, it would be preferable for the fields to always get set the same way - so you might have ctors like:

public Bar() : this("") {}
public Bar(string foo) {Foo = foo;}

编辑：作为一个方面的评论，请注意，在上面，如果有其他字段（未显示）与现场初始化，那么他们只能直接调用基地（构造函数初始化.. 。） - 即公开栏（串富）构造函数。其他构造确实的不的运行字段初始，因为它知道他们所做的此（...）男星。

edit: as a side comment, note that in the above, if there are other fields (not shown) with field initializers, then they are only directly initialized in the constructors that call base(...) - i.e. the public Bar(string foo) ctor. The other constructor does not run field initializers, since it knows they are done by the this(...) ctor.

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