Is C# a strongly typed or a weakly typed language?

Presented as a dialogue, as is my wont!

Is C# a strongly typed or a weakly typed language?

Yes.

That is unhelpful.

I don't doubt it. Interestingly, if you rephrased the question as an "and" question, the answer would be the same.

What? You mean, is C# a strongly typed and a weakly typed language?

Yes, C# is a strongly typed language and a weakly typed language.

I'm confused.

Me too. Perhaps you should tell me precisely what you mean by "strongly typed" and "weakly typed".

Um. I don't actually know what I mean by those terms, so perhaps that is the question I should be asking. What does it really mean for a language to be "weakly typed" or "strongly typed"?

"Weakly typed" means "this language uses a type verification system that I find distasteful", and "strongly typed" means "this language uses a type system that I find attractive".

No way!

Way, dude.

Really?

These terms are meaningless and you should avoid them. Wikipedia lists eleven different meanings for "strongly typed", several of which contradict each other. Any time two people use "strongly typed" or "weakly typed" in a conversation about programming languages, odds are good that they have two subtly or grossly different meanings in their heads for those terms, and are therefore automatically talking past each other.

But surely they mean something other than "unattractive" or "attractive"!

I do exaggerate somewhat for comedic effect. So lets say: a more-strongly-typed language is one that has some restriction in its type system that a more-weakly-typed language it is being compared to lacks. That's all you can really say without more context.

How can I have sensible conversations about languages and their type systems then?

You can provide the missing context. Instead of using "strongly typed" and "weakly typed", actually describe the restriction you mean. For example, C# is for the most part a statically typed language, because the compiler determines facts about the types of every expression. C# is for the most part a type safe language because it prevents values of one static type from being stored in variables of an incompatible type (and other similar type errors). And C# is for the most part a memory safe language because it prevents accidental access to bad memory.

Thus, someone who thinks that "strongly typed" means "the language encourages static typing, type safety and memory safety in the vast majority of normal programs" would classify C# as a "strongly typed" language. C# is certainly more strongly typed than languages that do not have these restrictions in their type systems.

But here's the thing: because C# is a pragmatic language there is a way to override all three of those safety systems. Cast operators and "dynamic" in C# 4 override compile-time type checking and replace it with runtime type checking, and "unsafe" blocks allow you to turn off type safety and memory safety should you need to. Someone who thinks that "strongly typed" means "the language absolutely positively guarantees static typing, type safety and memory safety under all circumstances" would quite rightly classify C# as "weakly typed". C# is not as strongly typed as languages that do enforce these restrictions all the time.

So which is it, strong or weak? It is impossible to say because it depends on the point of view of the speaker, it depends on what they are comparing it to, and it depends on their attitude towards various language features. It's therefore best to simply avoid these terms altogether, and speak more precisely about type system features.

Comments

• Anonymous
  October 15, 2012
  Excellent post, as usual. "C# is not as strongly typed as languages that do enforce these restrictions all the time." Can anyone mention here some of these languages.

• Anonymous
  October 15, 2012
  My favorite definition is that how "strongly typed" a language is measures the degree to which circumventing type restrictions is considered bad coding practice by its programming community. This definition has the advantages of being completely orthogonal to static typing (and every other feature of a type system), of aligning well with many informal uses of the term, and of being patently absurd as a way of describing languages.

• Anonymous
  October 15, 2012
  @Eric: ADA comes to mind. They have a very strict type system (A string of length 5 is not assignable into a string variable of length 6, for example).

• Anonymous
  October 15, 2012
  @Eric Not sure, but maybe Haskell? No pointersunsafe mode. No dynamic. No casting (?).

• Anonymous
  October 15, 2012
  "as is my wont!" -  It must have taken a lot of strong typing to add such an excellent phrase that is often underutilized in today's discourse.

• Anonymous
  October 15, 2012
  While I would classify Haskell as perhaps more 'strongly' typed than C#, there are still ways to get around its typing discipline. There are dynamic types (Data.Dynamic), casts, both safe (Data.Typeable.cast) and unsafe (Unsafe.Coerce.unsafeCoerce), and pointers (mostly used for interfacing with C).

• Anonymous
  October 15, 2012
  You left out anything about the "dynamic" keyword/type. I think maybe for the public at large's sake (as your blog is often regarded as a definitive source on C#) that you should mention dynamic and how it throws an additional wrench into the picture.

• Anonymous
  October 15, 2012
  > Not sure, but maybe Haskell? No pointersunsafe mode. No dynamic. No casting (?). Technically, Haskell has a whole host of unsafe "modes": www.haskell.org/hoogle the parent of all unsafe* being unsafePerformIO which allows bypassing the IO monad and performing IO from anywhere (which may completely crash the runtime, or result in very wacky behavior, such as the IO code being called a million times in a second due to STM). Casts and pointers are part of the unsafe* stuff (unsafeCoerce, unsafe*Ptr). There are also dynamic types: hackage.haskell.org/.../Data-Dynamic.html but they're kind-of safe (see fromDyn and fromDynamic)

• Anonymous
  October 15, 2012
  Hi Eric, My question isn't actually in relation to this posts topic, although I will mention a "dynamically typed" language... :-) Not sure where else to direct questions to you. Message cascades were recently added to the Dart programming language: news.dartlang.org/.../method-cascades-in-dart-posted-by-gilad.html Was just wondering, is it in the realm of possibility for these to appear in a future version of C#? Or is there something in their design which makes them incompatible with C#? I like that folks would no longer have to design their APIs to be "fluent". I have a personal library of extension methods for making WPF more fluent (github.com/.../FluentWpf). Message cascades in C# would eliminate the need for things like FluentWpf. Message cascades also appear to make object initializer syntax (new Obj() { abc = 10 }) unnecessary (although I realize, that's here to stay). Thanks for any insight! Signed, Envious of Dart programmers right now

• Anonymous
  October 15, 2012
  @dharmatech Visual Basic has that. msdn.microsoft.com/.../wc500chb.aspx

• Anonymous
  October 15, 2012
  Eric : "...C# is a pragmatic language ..." DBJ : Is C++ "a pragmatic language" ?

• Anonymous
  October 15, 2012
  What do you think about the term Manifest vs. Latent typing?

• Anonymous
  October 15, 2012
  The comment has been removed

• Anonymous
  October 15, 2012
  And sometimes it depends on the C# grammar :) -> enum test : int // COMPILES -> enum test2 : System.Int32 // DOES NOT COMPILE (integral-type expected)

• Anonymous
  October 15, 2012
  @Chris Eargle: I guess you missed the for the most part bit.

• Anonymous
  October 16, 2012
  MgSm88: It's in the penultimate paragraph.

• Anonymous
  October 16, 2012
  Not sure I agree that C# is ever weakly typed (without tedious user intervention). Can you show an example of what you mean? PS: My normal criteria for a weakly typed language is "if it looks like a number, it can be one, no matter the backing type".

• Anonymous
  October 16, 2012
  I think C++ is the same thing. It is type-safe but also allows casts. Seems like a lot of languages are "strongly-typed" AND "weakly-typed."

• Anonymous
  October 16, 2012
  Is the gist of today's blog that strongly/weak typing is a Partial-Ordering?

• Anonymous
  October 16, 2012
  leppie, That just demonstrates Eric's point about how "strongly-typed" and "weakly-typed" don't have widely-accepted definitions. Personally, to avoid confusion, I would propose using the term "horribly-typed" to refer to the languages that fit your criteria of "weakly-typed." :)

• Anonymous
  October 16, 2012
  The comment has been removed

• Anonymous
  October 16, 2012
  I've been hearing these type definitions for a long time, but I never completelly understood them until now.

• Anonymous
  October 17, 2012
  Is C# a strongly typed or a weakly typed language? Well, it depends how hard I hit the keyboard keys when I'm programming. :-)

• Anonymous
  October 17, 2012
  Not suprisingly (given that this is a question of semantics), you're playing a bit of a semantic game here. The argument seems to be 'Since I can get around C#'s type enforcement, it's not really a strongly typed language'.. which is like arguing that since I can remove the brakes in my car, clearly the car is inherently unsafe. It's technically true, but only when you consider the worst cases, rather than the typical and ignores the notion of 'intent'. Oddly, I thought you were going to go in a different direction - and argue that the dynamic extensions to C# render it weakly typed (ie: var, but as we all know, var isn't actually var). 'Object' is a better example of that dynamic nature - but it's been around since the start. To most programmers, I believe, the term 'strongly typed' means "the compiler expects me to know the types for variables and data and get them right at compile time, not deferring it to run time unless I explicitly tell the compiler I'm doing something weird - otherwise, it will say 'no'". That may not be a formal definition - but it's certainly how most people use the term. So is C# strongly typed? Best answer I have is 'most of the time'.

• Anonymous
  October 17, 2012
  Great Article. C# doesn't enforce these 3 safety systems all time but only most time, but this can allow risky developers to get performance gain in performance critical jobs. Java enforce these safety systems all time , but usually this drop performance making applications as eclipse and netbeans much slower than monodevelop and sharpdevelop, with no way out to increase performace.

• Anonymous
  October 17, 2012
  @  Commentor Eric: Java is strongly typed that do enforce these restrictions all the time. 1-Java doesn't allow any use of pointers at all, no  way to override this with "unsafe" 2-Java doesn't allow "dynamic" but java is weakly typed as : 1-It removes type information from generics in compile time (type erasure) since java 5 but type information will be reserved to be checked during runtime starting from java 8 insha'Allah On the other hand C# is reserving type info in generics for runtime checking since .net 2 2- Java as c# allow cast operators

• Anonymous
  October 17, 2012
  what the means of type verification and type system here?

• Anonymous
  October 17, 2012
  The comment has been removed

• Anonymous
  October 17, 2012
  The comment has been removed

• Anonymous
  October 17, 2012
  Interesting read. At the end I was imagining Eric as Obi-wan Kenobi in "Return of the Jedi", when he was talking about it depends on your point of view regarding Darth Vader.

• Anonymous
  October 20, 2012
  c# i think is a weakly typed language i.e it will find some loophole to do some implicit type conversion for nearly matching types' input arguments.

• Anonymous
  October 25, 2012
  Excellent post,Nice and subtle approach to define what makes C# strongly typed

• Anonymous
  October 30, 2012
  The comment has been removed

• Anonymous
  October 31, 2012
  The comment has been removed

• Anonymous
  October 31, 2012
  The comment has been removed

• Anonymous
  November 28, 2012
  the "Weakly Typed Languages" article at www.i-programmer.info/programming/theory/1469-type-systems-demystified-part2-weak-vs-strong.html?start=1 and the "Strong Typing" one at www.i-programmer.info/programming/theory/1515-strong-typing.html (parts of the "Type Systems Demystified" series at www.i-programmer.info/programming/theory/604-type-systems-demystified.html) attempt to explain the differences between weak and strong typing by comparing the type systems of Perl,C# and VB.NET and how C#'s dynamic type changes the game (especially in the "C# Perl-like behavior?" section). Although very educational (I hope),the point of the articles is to show that in the end "These terms are meaningless and you should avoid them" as you have already pointed out