问题
Possible Duplicate:
ReSharper and var
After I have installed ReSharper it demands(by warnings) that I use var whenever possible, for example
UnhandledExceptionEventArgs ue = (UnhandledExceptionEventArgs) t;
ReSharper wants to turn it into
var ue = (UnhandledExceptionEventArgs) t;
I like the first version better, is there any reason to prefer var? better performance? anything? or is it just a code style?
回答1:
It's really just a coding style. The compiler generates the exact same for both variants.
See also here for the performance question:
- Will using 'var' affect performance?
回答2:
When you say "by warnings" what exactly do you mean? I've usually seen it giving a hint that you may want to use var, but nothing as harsh as a warning.
There's no performance difference with var - the code is compiled to the same IL. The potential benefit is in readability - if you've already made the type of the variable crystal clear on the RHS of the assignment (e.g. via a cast or a constructor call), where's the benefit of also having it on the LHS? It's a personal preference though.
If you don't want R# suggesting the use of var, just change the options. One thing about ReSharper: it's very configurable :)
回答3:
As the others have said, there is no difference in the compiled code (IL) when you use either of the following:
var x1 = new object();
object x2 = new object;
I suppose Resharper warns you because it is [in my opinion] easier to read the first example than the second. Besides, what's the need to repeat the name of the type twice?
Consider the following and you'll get what I mean:
KeyValuePair<string, KeyValuePair<string, int>> y1 = new KeyValuePair<string, KeyValuePair<string, int>>("key", new KeyValuePair<string, int>("subkey", 5));
It's way easier to read this instead:
var y2 = new KeyValuePair<string, KeyValuePair<string, int>>("key", new KeyValuePair<string, int>("subkey", 5));
回答4:
In this case it is just coding style.
Use of var is only necessary when dealing with anonymous types.
In other situations it's a matter of taste.
来源：https://stackoverflow.com/questions/4868477/why-should-i-use-var-instead-of-a-type