我已经阅读了大量关于c# v4附带的新关键字的文章,但我无法区分“dynamic”和“var”之间的区别。
这篇文章让我思考了一下,但我还是看不出有什么不同。
你是否只能将“var”用作局部变量,但同时用作局部变量和全局变量?
你能显示一些代码没有动态关键字,然后显示相同的代码与动态关键字吗?
我已经阅读了大量关于c# v4附带的新关键字的文章,但我无法区分“dynamic”和“var”之间的区别。
这篇文章让我思考了一下,但我还是看不出有什么不同。
你是否只能将“var”用作局部变量,但同时用作局部变量和全局变量?
你能显示一些代码没有动态关键字,然后显示相同的代码与动态关键字吗?
当前回答
Do not confuse dynamic and var. Declaring a local variable using var is just a syntactical shortcut that has the compiler infer the specific data type from an expression. The var keyword can be used only for declaring local variables inside a method while the dynamic keyword can be used for local variables, fields, and arguments. You cannot cast an expression to var, but you can cast an expression to dynamic. You must explicitly initialize a variable declared using var while you do not have to initialize a variable declared with dynamic.
其他回答
Var只是普通类型声明的简写,让编译器猜测正确的类型。
Dynamic是一种新的(静态)类型,其中所有检查都在运行时完成,而不是由编译器完成。
一个很大的不同——你可以有一个动态返回类型。
dynamic Foo(int x)
{
dynamic result;
if (x < 5)
result = x;
else
result = x.ToString();
return result;
}
用var声明的变量是隐式的,但是是静态类型的。使用dynamic声明的变量是动态类型的。CLR添加此功能是为了支持Ruby和Python等动态语言。
我应该补充一点,这意味着动态声明在运行时解析,var声明在编译时解析。
Do not confuse dynamic and var. Declaring a local variable using var is just a syntactical shortcut that has the compiler infer the specific data type from an expression. The var keyword can be used only for declaring local variables inside a method while the dynamic keyword can be used for local variables, fields, and arguments. You cannot cast an expression to var, but you can cast an expression to dynamic. You must explicitly initialize a variable declared using var while you do not have to initialize a variable declared with dynamic.
下面是一个简单的例子,演示了动态(4.0)和Var之间的差异
dynamic di = 20;
dynamic ds = "sadlfk";
var vi = 10;
var vsTemp= "sdklf";
Console.WriteLine(di.GetType().ToString()); //Prints System.Int32
Console.WriteLine(ds.GetType().ToString()); //Prints System.String
Console.WriteLine(vi.GetType().ToString()); //Prints System.Int32
Console.WriteLine(vsTemp.GetType().ToString()); //Prints System.String
**ds = 12;** //ds is treated as string until this stmt now assigning integer.
Console.WriteLine(ds.GetType().ToString()); **//Prints System.Int32**
**vs = 12**; //*Gives compile time error* - Here is the difference between Var and Dynamic. var is compile time bound variable.
湿婆Mamidi