The evilness of 'var' in C#? [duplicate]

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Closed 11 years ago.

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C# 'var' keyword versus explicitly defined variables

EDIT:

For those who are still viewing this, I've completely changed my opinion on var. I think it was largely due to the responses to this topic that I did. I'm an avid 'var' user now, and I think its proponents comments below were absolutely correct in pretty much all cases. I think the thing I like most about var is it REALLY DOES reduce repetition (conforms to DRY), and makes your code considerably cleaner. It supports refactoring (when you need to change the return type of something, you have less code cleanup to deal with, and NO, NOT everyone has a fancy refactoring tool!), and anecdotally, people don't really seem to have a problem not knowing the specific type of a variable up front (its easy enough to "discover" the capabilities of a type on-demand, which is generally a necessity anyway, even if you DO know the name of a type.)

So here's a big applause for the 'var' keyword!!

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This is a relatively simple question...more of a poll really. I am a HUGE fan of C#, and have used it for over 8 years, since before .NET was first released. I am a fan of all of the improvements made to the language, including lambda expressions, extension methods, LINQ, and anonymous types. However, there is one feature from C# 3.0 that I feel has been SORELY misused....the 'var' keyword.

Since the release of C# 3.0, on blogs, forums, and yes, even Stackoverflow, I have seen var replace pretty much every variable that has been written! To me, this is a grave misuse of the feature, and leads to very arbitrary code that can have many obfuscated bugs due to the lack in clarity of what type a variable actually is.

There is only a single truly valid use for 'var' (in my opinion at least). What is that valid use, you ask? The only valid use is when you are incapable of knowing the type, and the only instance where that can happen:

When accessing an anonymous type

Anonymous types have no compile-time identity, so var is the only option. It's the only reason why var was added...to support anonymous types.

So...whats your opinion? Given the prolific use of var on blogs, forums, suggested/enforced by tools like ReSharper, etc. many up and coming developers will see it as a completely valid thing.

• Do you think var should be used so prolifically?
• Do you think var should ever be used for anything other than an anonymous type?
• Is it acceptable to use in code posted to blogs to maintain brevity...terseness? (Not sure about the answer this one myself...perhaps with a disclaimer)
• Should we, as a community, encourage better use of strongly typed variables to improve code clarity, or allow C# to become more vague and less descriptive?

I would like to know the communities opinions. I see var used a lot, but I have very little idea why, and perhapse there is a good reason (i.e. brevity/terseness.)

Answer 1

I have to dissent with the view that var reduces redundancy in any meaningful way. In the cases that have been put forward here, type inference can and should come out of the IDE, where it can be applied much more liberally with no loss of readability.

Answer 2

If you feel that giving the same information twice reduces errors (the designers of many web forms that insist you type in your email address twice seem to agree), then you'll probably hate var. If you write a lot of code that uses complicated type specifications then it's a godsend.

EDIT: To exapand this a bit (incase it sounds like I'm not in favour of var):

In the UK (at least at the time I went), it was standard practice to make Computer Science students learn how to program in Standard ML. Like other functional languages it has a type system that puts languages in the C++/Java mould to shame.

Anyway, what I noticed at the time (and heard similar remarks from other students) was that it was a nightmare to get your SML programs to compile because the compiler was so increadibly picky about types, but once the did compile, they almost always ran without error.

This aspect of SML (and other functional languages) seems to be one the questioner sees as a 'good thing' - i.e. that anything that helps the compiler catch more errors at compile time is good.

Now here's the thing with SML: it uses type inference exclusively when assigning. So I don't think type inference can be inherently bad.

Answer 3

I agree with others that var eliminates redundancy. I have decided to use var where it eliminates redundancy as much as possible. I think consistency is important. Choose a style and stick with it through a project.

Answer 4

As Earwicker indicated, there are some functional languages, Haskell being one and F# being another, where such type inference is used much more pervasively -- the C# analogy would be declaring the return types and parameter types of methods as "var", and then having the compiler infer the static type for you. Static and explicit typing are two orthogonal concerns.

In fact, is it even correct to say that use of "var" is dynamic typing? From what I understood, that's what the new "dynamic" keyword in C# 4.0 is for. "var" is for static type inference. Correct me if I am wrong.

Answer 5

var is a splendid idea to help implement a key principle of good programming: DRY, i.e., Don't Repeat Yourself.

VeryComplicatedType x = new VeryComplicatedType();

is bad coding, because it repeats VeryComplicatedType, and the effects are all negative: more verbose and boilerplatey code, less readability, silly "makework" for both the reader and the writer of the code. Because of all this, I count var as a very useful enhancement in C# 3 compared to Java and previous versions of C#.

Of course it can be mildly misused, by using as the RHS an expression whose type is not clear and obvious (e.g., a call to a method whose declaration may be far away) -- such misuse may decrease readability (by forcing the reader to hunt for the method's declaration or ponder deeply about some other subtle expression's type) instead of increasing it. But if you stick to using var to avoid repetition, you'll be in its sweet spot, and no misuse.

Answer 6

Pop quiz!

What type is this:

var Foo = new string[]{"abc","123","yoda"};

How about this:

var Bar = {"abc","123","yoda"};

It takes me roughly no longer to determine what types those are than with the explicity redundant specification of the type. As a programmer I have no issues with letting a compiler figure out things that are obvious for me. You may disagree.

Cheers.