When Should You—and Shouldn't You—Use `var` for Type Inference in C#?

The best practice of using types in infer of keywords

in the c# var C# 3.0 introduced

Keywords to allow types to infer the type of variables, thereby simplifying the code and improving readability. However, excessive use of may also cause type safety problems.

var var Improper use

Using var will reduce the readability and maintenance of the code in the following circumstances, increase the potential errors:

var The reasonable use of

foreach (var item in someList) { // 'item' 的类型不明确
    // ...
}
var something = someObject.SomeProperty; // 'something' 的类型不明确
var something = someMethod(); // 'something' 的类型不明确

In the following circumstances, using can improve the readability of the code without affecting type security: var

linq query and

var

var l = new List<string>(); //  `l` 的类型一目了然
var s = new SomeClass(); // `s` 的类型一目了然

The use of

in the Linq query is more subtle: var Although the compiler can infer the type of

, its type information is not intuitive compared to direct declaration variable types.

var linq to objects and

var results = from r in dataContext.SomeTable
              select r; // `results` 的具体类型并非完全清晰

results Using

more cautious in Linq to Objects:

var This is similar to , and there are hidden dangers of types of security. When calling the heavy load method, it is easy to pass in the type of non -matching type, resulting in runtime errors.

and type security var

var results = from item in someList
              where item != 3
              select item;

Although maintains the strong type of C#, the hidden type information may cause problems, especially when the method is overloaded, the compiler may not be able to detect the type not matching during compilation.

foreach (var item in someList) Conclusion

Keywords can improve the readability and simplicity of the code under appropriate circumstances, but it needs to be used with caution. When the type is not clear, the risk may be increased, and the use of var should be avoided. For Linq queries and Linq To Objects, the importance of weighing readability and type security needs to be weighing. Use to make the code clearer and more concise, while maintaining the robustness and maintenance of the program.

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