总结一下const和readonly有这么几条区别:
- const和readonly的值一旦初始化则都不再可以改写;
- const只能在声明时初始化;readonly既可以在声明时初始化也可以在构造器中初始化;
- const隐含static,不可以再写static const;readonly则不默认static,如需要可以写static readonly;
- const是编译期静态解析的常量(因此其表达式必须在编译时就可以求值);readonly则是运行期动态解析的量;
- const既可用来修饰类中的成员,也可修饰函数体内的局部变量;radonly只可以用于修饰类中的成员
在许多教程中常看到列出了两者之间的区别
const
(1)在编译期间解析常量
(2)必须在申明时就初始化
(3)即可用来修饰类中的成员,也可用来修饰函数中的局部变量
static readonly
(1)在运行期间解析常量
(2)即可在申明时初始化,也可在构造器中初始化
(3)只可用来修饰类中的成员
从上面的区别看似乎也很明白,可是在实际的使用中还是不太好把握。在c#中有两种不同的常量:
静态常量(compile-time constants) 和动态常量(runtime constants),他们之间有不同的特性,错误的使用不仅会损失效率,
还可能造成错误。相比之下,静态常量在速度上会稍快写,但是灵活性却比动态常量差。
从我个人对他们的使用中总结出有如下三点需要注意:
(1)当使用new来初始化一个常量,不管他是值类型,还是引用类型都只能使用static readonly
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(2) 比较编译时和运行时他们之间的区别
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static readonly A=B*20;
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static readonly B=10;
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//在编译的时候B并没有被编译为10,A也没有被编译为200
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const A=B*20
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const B=10
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//显然在编译的时候,就把B编译为10,A编译为200了,而不是在运行时计算B*20
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(3)在不同的项目中使用const和static readonly的区别
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