C# Member Variables: Field Initialization vs. Constructor Initialization—Which is Best?

C# member variable initialization: best practice

When declaring member variables in C#, there are two main initialization methods: direct assignment at declaration or initialization in the default constructor. This article explores the pros and cons of each approach and discusses the performance implications.

Field initialization and constructor initialization

Field initialization means directly assigning values ​​to member variables when declaring them. For example:

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

On the other hand, constructor initialization refers to assigning values ​​to member variables in the default constructor. For example:

private List<object> _things;
private int _arb;

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

Performance Considerations

In terms of performance, there is no significant difference between field initialization and constructor initialization. Both methods essentially implement the initialization logic in the constructor. The only slight difference is that field initializers occur before any "base" or "this" constructor calls.

Auto-implemented properties

When using automatically implemented properties, the constructor approach becomes more appropriate. Auto-implemented properties do not allow field initialization, so they must be initialized in the constructor. For example:

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

Preferences and Style

In addition to the above considerations, the choice between field initialization and constructor initialization largely depends on personal preference and coding style. However, there are some general guidelines:

• Field initialization: If the initialization is simple and does not require complex logic, field initialization can be used first to keep the code organized and localized.
• Constructor initialization: Constructor initialization is more appropriate if the initialization requires complex logic or involves constructor parameters.

Conclusion

The best practice for initializing member variables in C# depends on the specific needs of your code. While there is no difference in performance, field initialization localizes the initialization logic, while constructor initialization allows for more complex scenarios. By considering the pros and cons of each method, developers can choose the method that works best for their code.

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