26

Obviously there can't be an instance member on a static class, since that class could never be instantiated. Why do we need to declare members as static?

Soner Gönül
  • 97,193
  • 102
  • 206
  • 364
richard
  • 12,263
  • 23
  • 95
  • 151
  • 5
    Didn't you just answer your own question? I believe the only other answer as to "why" is that the C# language team didn't think of implicitly treating all members of a static class as static. Or they consciously decided against it. Does it really matter? – SirViver May 14 '11 at 22:16
  • 1
    Probably because it simplifies reading code at the expense of forcing the programmer to add a single keyword. This way, even if you don't see the class declaration, you will _always_ know that the given member is `static`. Similarly, even if you do see the class declaration, there will be no confusion when people mix and match supplying it versus not supplying it. – pickypg May 14 '11 at 22:17
  • 3
    @SirViver: It doesn't really _matter_, but it's a question . . . that's why I put it up here. :-) – richard May 14 '11 at 22:19
  • The whole point of my question is that yes I know it would be syntactic sugar, but why did they leave this sugar out. My only thought is that the designers favored "readability" over "terseness" this time. – richard May 14 '11 at 22:27
  • @Richard DesLonde, if you skipped the It seems annoying. part, this has the potential to deliver an interesting answer. – Caspar Kleijne May 14 '11 at 22:32
  • @Caspar: Good point. Revised! – richard May 14 '11 at 22:35
  • 2
    See also related question http://stackoverflow.com/questions/2631975/c-using-consts-in-static-classes – Eric Lippert May 14 '11 at 22:39
  • >since that class could never be instantiated Not now - but it could in the future if it becomes a non-static class. – tymtam Jul 13 '12 at 05:06
  • It's damn annoying for me too, however I see where they were coming from when they decided that. – Sasino Jun 28 '22 at 19:23

8 Answers8

45

I get asked questions like this all the time. Basically the question boils down to "when a fact about a declared member can be deduced by the compiler should the explicit declaration of that fact be (1) required, (2) optional, or (3) forbidden?"

There's no one easy answer. Each one has to be taken on a case-by-case basis. Putting "static" on a member of a static class is required. Putting "new" on a hiding, non-overriding method of a derived class is optional. Putting "static" on a const is forbidden.

Briefly considering your scenario, it seems bizarre to make it forbidden. You have a whole class full of methods marked "static". You decide to make the class static and that means you have to remove all the static modifiers? That's weird.

It seems bizarre to make it optional; suppose you have a static class and two methods, one marked static, one not. Since static is not normally the default, it seems natural to think that there is intended to be a difference between them. Making it optional seems to be potentially confusing.

That leaves making it required, as the least bad of the three options.

See http://blogs.msdn.com/b/ericlippert/archive/2010/06/10/don-t-repeat-yourself-consts-are-already-static.aspx for more thoughts on these sorts of problems.

Eric Lippert
  • 647,829
  • 179
  • 1,238
  • 2,067
  • I see your point but how about e.g private then? Not quite te same, but pretty optional. Or is it optional because it is default? – Caspar Kleijne May 14 '11 at 22:35
  • 1
    @Caspar: what about "private"? Because it is the default, it's optional. And because the default is the *most restrictive*, it is harmless to accidentally leave it off; you can't expose more than you intend, only less. – Eric Lippert May 14 '11 at 22:37
  • @Eric: I was hoping you would weigh in! Is this what you intended to say: "you have a method marked as static and a method not marked as static" or did you mean this "you have a **class** marked as static and a method not marked as static"? If the former then I am a bit confused by that statement. – richard May 14 '11 at 22:38
  • 1
    @Eric: So I guess the difference between this decision and the decision you made with constants is that constants can't be anything _but_ static, so it makes sense to make it illegal since it's inherent in the type. Whereas with other class members (methods, properties, etc.), they could be static, or not, and so it's better to make it explicit for readability and to avoid confusion. – richard May 14 '11 at 22:50
  • @Eric: By the way, thanks for the link to the blog post and the SO question about constants. – richard May 14 '11 at 22:51
  • This all makes sense, but the reality is that copy-pasting methods across static and non-static classes would be more complicated if the signatures would differ and this is the real reason ;) – tymtam Jul 13 '12 at 05:03
  • One could argue that there are 4 or 5 options, depending on how you count them. `private` is fully optional as neither absence or presence raises a warning (some source analysis tools have an opinion and do, but that's someone else's call), while `new` being absent does raise a warning when it hides. So: 1. Required, 2. Forbidden, 3. Optional, no warning, 4. Optional, warn on presence, 5. Optional warn on absence. – Jon Hanna Nov 23 '15 at 10:42
  • I disagree about the "weird" comment when changing an instance class to a static class. First of all, this should very rarely happen considering the vast differences in semantics (how often will you have an instance class that needs to change to static besides very early in development?). Secondly, because the semantics are so different, I don't think it should be weird at all to force the removal of the static declaration. I very much appreciate the problem abstraction at the beginning of the answer though. Well put per usual. – aaaaaa Aug 13 '17 at 14:51
5

Because by definition, all of their members must be static. They decided not to give some confusing syntactic sugar.

soandos
  • 4,978
  • 13
  • 62
  • 96
  • 1
    I know but there is confusing syntactic sugar all throughout the C# language. In fact, they keep adding to it. Why they left this out is beyond me. – richard May 14 '11 at 22:18
  • 1
    To make it clear that all of those elements are static. It would be pretty confusing not having something declared as static, but it being static. Can't comment on the rest of the language. – soandos May 14 '11 at 22:20
  • I have to say they make a good decision on explicitly stating member is a static. Think about .NET 4.0 var. It is easy to use, but for inexperience developers it can get confusing because the type wasn't explicit. – dsum May 14 '11 at 22:38
3

I would go one step further and ask: Why does C# have static classes at all? It seems like a weird concept, a class that's not really a class. It's just a container, you can't use it to type any variables, parameters or fields. You also can't use it as a type parameter. And of course, you can never have an instance of such a class.

I'd rather have modules, like in VB.NET and F#. And then, the static modifier would not be necessary to avoid confusion.

Jordão
  • 55,340
  • 13
  • 112
  • 144
2

It could be implicit, but also it would complicate code reading and lead to confusions.

Alex Aza
  • 76,499
  • 26
  • 155
  • 134
2

Richard,

Hmmmm... I'd guess that the language designers decided that it would be better to be very, very explicit... to avert any possible confusion when a maintainer, who doesn't know the code, jumps into the middle of a static class, and presumes that they are in a "normal" instance context.

But of course, that's just a guess. Most IDE's help you out there anyway, by adding the static modifier "automagically"... or at least highlighting your mistake at "write time", as apposed to "compile time".

It's a good question... unfortunately not one with a "correct" answer... unless someone can turn up a link from a C#-language-designers blog (or similar) discussing this decision. What I can tell you is: "I'd bet $1,000 that it's no accident."

Cheers. Keith.

Rick Sladkey
  • 33,988
  • 6
  • 71
  • 95
corlettk
  • 13,288
  • 7
  • 38
  • 52
  • 2
    @Eric, Dude... Got proof of that? I'd like to read the designers thoughts, that's all... Like I said, I'm pretty damn confident that it's NO accident... I just can't "prove" it. – corlettk May 14 '11 at 22:28
  • @corlettk now you can read the designers thoughts, see Eric's answer! – David Heffernan May 14 '11 at 22:41
  • 7
    Right; you're asking for an opinion from one of the C# language designers, and you've got one. I'm a member of the C# language design committee. – Eric Lippert May 14 '11 at 22:43
  • 1
    corlettk, Eric is part of C# design team (and one who shares lot of details behind the design decisions made by the team) so if he says that it was 'no accident'. That's a proof enough for me. :) – SolutionYogi May 14 '11 at 22:44
  • When you want to be anonymous, everyone recognizes you. When it would be nice to be famous, no one knows who you are. Sometimes you just can't win. – Rick Sladkey May 15 '11 at 03:57
  • @Eric: Are there times where when you all want to make a design decision, someone's bias negatively affects the outcome? I don't know if everyone has equal vote there, but like if someone higher up like Anders thinks it's better to have it this way, instead of another way, because of his background, and his favor towards a certain way of doing things? Also do you think it would be interesting if the design decisions were driven by public via some sort of poll in some unique way, where the poll is created by you and actual customers cast their vote as to which way is better. Just curious :O – Joan Venge May 15 '11 at 04:30
  • 3
    @Joan: It's a benevolent dictatorship, though occasionally things do come to a vote. It is certainly beneficial to get ideas from the public, but you know, if we drove the design process strictly by public input, great features like LINQ would never happen. It's not like we got a lot of mail saying "please add query comprehensions based on the sequence monad to C#". – Eric Lippert May 15 '11 at 06:47
  • Eric, forgive my ignorance... I was blissfully unaware of that you where/are involved in the language design team. Shucks. Now I've been put down by one of the best... How will I ever top that? – corlettk May 15 '11 at 06:51
  • Thanks Eric. By voting I mainly meant you decide the options with clear examples and people vote. It could even be like you would have an application for this, for areas of game programming, audio programming, database programming, etc to get a better sample where the numbers would be limited, and the people would be approved based on their usage, etc and with those serious people, you could open a voting similar to how uservoice.com provides polls, and people would have limited number of votes, etc and not only they could vote, but they could also post syntax suggestions, etc (cont) – Joan Venge May 16 '11 at 04:25
  • For things like say `extensions everything`, where you could very well find some sample where someone really thoroughly thought this out and might like it. I think it would open a lot of doors. In addition of the existing list, people could also add new features so others can vote on it. Lastly since each feature potentially asks for syntax suggestions, etc in the end if they are decided to be implemented, people could vote on these suggestions but ultimately you could pick the one that's easiest to implement and use, etc. Feature wise if something is very domain specific (cont) – Joan Venge May 16 '11 at 04:29
  • it would be added as .NET library, but if it's a generic thing like Linq, it would be added to the language. This way also you wouldn't necessarily get bias towards C++ where I imagine a major part of the C# team has a strong background? Like some enthusiastic web developer could offer nicer syntax you guys didn't really think of. Anyway, was just thinking about it, not trying to put down your work :O Because it's close to perfection. – Joan Venge May 16 '11 at 04:31
  • 2
    @corlettk: no worries! @Joan: we have a group of MVPs and other industry insiders that we consult regularly on those sorts of things, and sometimes if we have a bunch of them in a room we'll do a "straw poll" sort of vote, but of course it is not binding. I'll also occasionally do straw polls on the blog if we need a quick sanity check from the community on whether a feature is confusing or not. – Eric Lippert May 16 '11 at 21:35
  • Thanks Eric. I knew you would have something like this already :O – Joan Venge May 16 '11 at 21:50
1

Explicit coding makes things maintainable

If I want to copy a method from one class to another, so that code is better organized, then I would have to keep cheking a lot of things all the time, just in case the destination class is or is not static.

By declaring the member as static, you also have a visual indication of what the code is, when you see it.

It is also less confusing. Imagine a class that is static, and inside it has got members marked as static, and others not marked.

I can see lots of reasons, and many other reasons exist.

Miguel Angelo
  • 23,796
  • 16
  • 59
  • 82
1

One reason I would think it is important to explicitly state it is a static is because in a multi-threaded programming model, these static variables are shared by multiple threads. When doing code review or code analysis, it is much easier to pick up this importance from reading the variable, instead of looking up the class declaration, and determine if the variables are static or non-static. It can get pretty confusing when reading variable during code review if you don't know if the class is static or non-static.

dsum
  • 1,433
  • 1
  • 14
  • 29
0

This is because copy-paste would be more complicated.

If you copy a method from a static class to a non-static class then you would have to add the static keyword.

If you copy a method from a non-static class to a static class you would have to remove the static keyword.

Moving methods around is the primary thing developers do ('I need to refactor this code, it will take a week at least'), and by making it easier Eric and his team allowed us to save hours of work.

tymtam
  • 31,798
  • 8
  • 86
  • 126