Visual Studio will automatically create using statements for you whenever you create a new page or project. Some of these you will never use.
Visual Studio has the useful feature to "remove unused usings".
I wonder if there is any negative effect on program performance if the using statements which are never accessed, remain mentioned at the top of the file.
An unused using has no impact to the runtime performance of your application.
It can affect the performance of the IDE and the overall compilation phase. The reason why is that it creates an additional namespace in which name resolution must occur. However these tend to be minor and shouldn't have a noticeable impact on your IDE experience for most scenarios.
It can also affect the performance of evaluating expressions in the debugger for the same reasons.
No, it's just a compile-time/coding style thing. .NET binaries use fully qualified names under the hood.
The following link A good read on why to remove unused references explains how it be useful to remove unused references from the application.
Below are the some excerpts from the link:
By removing any unused references in your application, you are
preventing the CLR from loading the unused referenced modules at
runtime. Which means that you will reduce the startup time of your
application, because it takes time to load each module and avoids
having the compiler load metadata that will never be used. You may
find that depending on the size of each library, your startup time
is noticeably reduced. This isn't to say that your application will
be faster once loaded, but it can be pretty handy to know that your
startup time might get reduced.
Another benefit of removing any unused references is that you will
reduce the risk of conflicts with namespaces. For example, if you
have both System.Drawing and System.Web.UI.WebControls referenced,
you might find that you get conflicts when trying to reference the
Image class. If you have using directives in your class that match
these references, the compiler can't tell which of the ones to use.
If you regularly use autocomplete when developing, removing unused
namespaces will reduce the number of autocompletion values in your
text editor as you type.
No effect on execution speed, but there may be some slight effect on compilation speed/intellisense as there are more potential namespaces to search for the proper class. I wouldn't worry too much about it, but you can use the Organize Usings menu item to remove and sort the using statements.
Code that does not execute does not affect the performance of a program.
No, there are several process involved when compiling a program. When the compiler start looking for references (classes, methods) it will use only the ones used on the code. The using directive only tells the compiler where to look. A lot of unused using statement could maybe have a performance issue but just at compile time. At runtime, all the outside code is properly linked or included as part of the binary.
Related
This question already has answers here:
Why remove unused using directives in C#?
(10 answers)
Closed 9 years ago.
Lately my coworker has been on something of a jihad against line counts. When I check in a new file, I'll generally leave all the referenced namespaces that Visual Studio includes, by default (System, System.Collections.Generic, and System.Linq being the majors that I almost always rely on). Several days later, my coworker will be reviewing diffs, see that maybe I haven't actually used any functions from the .Linq namespace, and he'll clip it. When I come back to the file some days later and want to add some functionality that depends on, say, .Select, my blood pressure shoots up when I see that the namespace is gone and I have to add it back.
My question is: aside from the marginal reduction in the project's line count, or the size of the source files, is there any real gain in clipping these unused namespaces? Is the .NET compiler so poor at analysis that unused namespaces induce a penalty in the outputted assemblies? If he's right in pursuing this madness, I'll accept it as a lesson learned... I just can't imagine that there's any sane reason for this. It seems like nothing but boneheaded craziness to me.
Definitely no benefits comparing to the time spent searching and clipping even though VS has an option to do cleaning. No major benefits except compile time benefits and clean coding.
For more info:
Why remove unused using directives in C#?
There won't be any perfomance boost like ou guess, but removing unwanted using is all about keeping your code clean, neat and readable.
Compiler will make use of only required and related assemblies we using in our code.
Make use of visual studio's Remove unused usings command and to remove unused namespaces to make your code lean and readable to another developer also.
At compile time, only utilised namespaces are compiled into the IL. Those that are unused are ignored.
Aside from a miniscule (and unnoticeable) delay in compilation whilst .Net is figuring out which namespaces you are using there is no impact what-so-ever on the output.
The Assembly class has a GetReferencedAssemblies method that returns the
referenced assemblies. Is there a way to find what Types are referenced?
The CLR wont be able to tell you at runtime. You would have to do some serious static analysis of the source files - similar to the static analysis done by resharper or visual studio.
Static analysis is fairly major undertaking. You basically need a c# parser, a symbol table and plenty of time to work through all the cases that come up in abstract syntax trees.
Why can't the CLR tell you at run time? It is just in time compiled, this means that CLR bytcode is converted into machine code just before execution. Reflection only tells you stuff known statically at runtime about your types, and the CLR would only know if a type is referenced when the code is run. The CLR only knows when a type is loaded at execution time - at the point of just in time compilation.
Use System.Reflection.Assembly.GetTypes().
Types are not referenced separately from assemblies. If an assembly references another assembly, it automatically references (at least in the technical context) all the types within that assembly, as well. In order to get all the types defined (not referenced) in an assembly, you can use the Assembly.GetTypes method.
It may be possible, but sounds like a rather arduous task, to scan an assembly for which actual types it references (i.e. which types it actually invokes or otherwise mentions). This will probably involve working with IL. Something like this is best to be avoided.
Edit: Actually, when I think about it, this is not possible at all. Whatsoever. On a quite basic level. The thing is, types can be instantiated and referenced willy-nilly. It's not even uncommon for this to happen. Not to mention late binding. All this means trying to analyze an assembly for all the types it references is something like predicting the future.
Edit 2: Comments
While the question, as stated, isn't possible due to all sorts of dynamic references, it is possible greatly shrink all sorts of binary files using difference encoding. This basically allows you to get a file containing the differences between two binary files, which in the case of executables/libraries, tends to be vastly smaller than either of the actual files. Here are some applications that perform this operation. Note that bsdiff doesn't run on Windows, but there is a link to a port there, and you can find many more ports (including to .NET) with the aid of Google.
XDelta
bsdiff
If you'd look, you'll find many more such applications. One of the best parts is, they are totally self-contained and involve very little work on your part.
If I put all classes of a project in the same namespace all classes are available everywhere in the project. But if I use different namespaces not all classes are available everywhere. I get a restriction.
Does using namespaces affect the compile time somehow? Since the compiler has less classes in each namespace and not all namespaces are used all the time he may have a little less trouble finding the right classes.
Will using namespaces affect the applications performance?
It won't affect the execution-time performance.
It may affect the compile-time performance, but I doubt that it would be significant at all, and I wouldn't even like to predict which way it will affect it. (Do you have an issue with long compile times? If so, you may want to try it and then measure the difference... otherwise you really won't know the effect. If you don't have a problem, it doesn't really matter.)
I'm quite sure, that putting classes in namespaces does not effect the compile time significantly.
But beware, that you might lose your logical project-structure, if you put every class into the same namespace.
I (and the Resharper) suggest to use namespaces that correspond with the file location (which corresponds with the project structure).
You should use namespaces according to your logic and ease of human readability and not for performance issues.
According to the question: Is C# code faster than Visual Basic.NET code?
Was said that C# and VB.NET generates the same CLR code at the end.
But in the case when I'm using codebehind and inline code, are there different performance (ignoring the language used)?
Inline code can require compilation the first time the request is made. After that (or if it's precompiled), there's absolutely zero difference between them.
By the way, even if it requires compilation, the speed difference should be insignificant as ASP.NET will have to compile a source file anyway. The difference will come down to a adding a few lines of code in a large source file!
Yes, ish... If you're compiling at run-time you're always going to be more expensive than something which doesn't have to, but that compile will be cached (if you will) after the first request so you'll get zero difference from then on.
There's probably somone who knows another reason, but to my mind the only realistic purpose for inline is the ability to make hot fixes without a rebuild + redeploy: the kind of thing you might do in small or early stage dev projects. Personally I also find inline just a little... aesthetically displeasing.
The aspx pages have to be parsed and compiled anyway as ASP.Net turns them into classes that inherit from the codebehind (hence the inherit attribute in the page directive) so compilation is necessary in either case. The difference between the two for first runs is going to be negligible unless we're talking about several thousand lines of code.
But I agree with anna: inline is icky.
I'm not sure whether the resulting assembly produced has the AllowOptimize attribute set to on or off. I can find no documentation which indicates this either way.
As such it is possible that the resulting code is not optimized by the JIT in quite the same way.
I doubt this makes a significant difference if any (like I said this might be controlled in some other way) but certainly it could impact certain operations if it, for example, disabled inlining and you had a large, extremely tight loop. Such a construct would probably be a poor choice within an asp.net page so this shouldn't be an issue.
No. Unless you are using web project the site needs to be compiled on the first hit. That affects inline as well as code behind to some extend. After that they run pretty much at the same speed.
I know VS2008 has the remove and sort function for cleaning up using directives, as does Resharper. Apart from your code being "clean" and removing the problem of referencing namespaces which might not exist in the future, what are the benefits of maintaining a "clean" list of using directives?
Less code?
Faster compilation times?
If you always only have the using directives that you need, and always have them appropriately sorted, then when you come to diff two versions of the code, you'll never see irrelevant changes.
Furthermore, if you have a neat set of using directives then anyone looking at the code to start with can get a rough idea of what's going to be used just by look at the using directives.
For me it's basically all about less noise (plus making Resharper happy!).
I would believe any improvement in compilation time would be minimal.
There's no runtime impact. It's purely compile time. It potentially impacts the following:
Less chance for Namespace collisions
Less "noise" in the code file
Very explicit about which namespaces and possible types to expect in the file
Using the menu to remove unused and Sort means more consistency with using statements among the devs. Less chance of dumb checkins just to fix it up.
Less noise.
Clear expectation of what types are used ("My UI layer depends upon System.Net. Wow, why?")
Cleaner references: if you have the minimal set of using statements, you can cleanup your references. Often I see developers just keep throwing references into their projects, but they never remove them when they're no longer needed. If you don't have anything that actually needs a reference (and a using statement counts), it becomes trivial to clean up your references. (Why would you want to do that? In large systems that have been decomposed into components it will streamline your build dependencies by eliminating the unused deps.)
For me, a clean list of using statements at the beginning can give a good understanding of the types to expect.
I saw a decent gain in compile time a few years ago when I first installed ReSharper (on an 18 project solution). Since then its just been about keeping it clean.
I can't speak to the benefits in compile time and performance, but there's a lower chance of namespace collisions if you have minimize your using declarations. This is especially important if you are using more than one third party library.
There is one compile-time difference: when you remove a reference, but still have a using directive in your code, then you get a compiler error. So having a clean list of using directives makes it a little bit easier to remove unused references.
Usually the compiler removes unused references, but I don't know if that works when a using is in the code.