You're not going to cover all of the correct behavior in any nontrivial software with unit tests unless you plan to spend 99% of your time writing unit tests. Static typing gives a good baseline of correctness.
Not really. Lets say you have an `add(a, b)` function. Static typing can guarantee that the function returns a number, but not that it returns the correct number. So you need unit tests anyway.
A unit test `assert_equal(4, add(2, 2))` actually tells you something about the correctness about the function, and it implicitly also verifies that it returns a number. So static typing does not save you anything.
Static typing does have advantages, for example for documentation and for automated refactoring. But it doesn't replace any unit tests.
> But if the tests verify that the output is correct, then it implicitly follows that the types are correct, so you get type checking for free.
Your unit test checks the correct behaviour for one out of infinite possible inputs. You don't 'get type checking for free' , what you get is no type checking at all.
If I understand you correctly, you a suggesting unit tests in a dynamic language should test all possible invalid inputs. Since statically typed languages eliminate a subset of invalid inputs (because they won't compile), statically typed languages saves you from writing some of these tests.
My argument is that you wouldn't write such tests in the first place since they provide little to no value.
If function `foo()` calls function `bar()` you want to ensure that foo passes the correct arguments. You don't do that by checking that bar() rejects all possible invalid types. You do it by checking that foo() actually works and provide the correct result. The types involved are an implementation detail.
But you're testing a tiny subset of possible scenarios of behaviour of the function. If you can anticipate all possible input types and value ranges, maybe unit tests are enough, but that's not realistic in a dynamic language/program where complex values are non-deterministically generated at runtime - based on user input, db, file, etc.
If you are talking about untrusted external input then yes, you need to carefully validate and reject invalid input. If you receive JSON or a CSV file or whatever, there are an infinite number of valid inputs and an infinite number of invalid inputs. But this is the same for statically typed languages, and the type-checker will not help you, since a valid JSON string and an invalid JSON string look exactly same to the type checker.
That's not at all the same problem, because here you're intentionally writing code that throws exceptions for some reason? Also, many languages, such as Java will not allow you to throw a checked exception that's not declared on the interface method - such issues will be statically checked and caught - thanks for proving my point ;)
> of valid inputs and an infinite number of invalid inputs. But this is the same for statically typed languages, and the type-checker will not help you, since a valid JSON string and an invalid JSON string look exactly same to the type checker.
Not at all, in a statically typed language the JSON would typically be deserialized into a structured type with all the benefits of type checking, validation and usage of the resulting values. Of course it's possible to just use a JSON string directly, but that's not idiomatic and generally not the way it's done in quality codebases.
Static typing is something you use for performance reasons primarily.
If you want to catch errors with static typing you need Haskell or Rust levels of support for it. C# / Java / C++ don't make the grade.
That is not how to decrease the complexity of reasoning about a Python program.
What you should do instead is break the program up into smaller microservices.
Errors that would be caught by static type checking are exceptionally rare when you do commerical development in dynamically typed languages.
You right now are complaining about a problem that only exists with inside your own head.
> Errors that would be caught by static type checking are exceptionally rare when you do commerical development in dynamically typed languages.
Those kinds of errors are not rare at all.
Dynamically typed languages tend to be simpler and easier to use. This means on the whole they have less bugs than their static typed counter parts.
The real issue with dynamically typed languages is that their performance sucks. (That and according to this thread people not having a clue on how they are properly used. You can't just use the same development techniques as you use in a statically typed language. It's different.)
And yet your comments demonstrate the opposite.
> Dynamically typed languages tend to be simpler and easier to use.
Very debatable.
> This means on the whole they have less bugs than their static typed counter parts.
Not at all.
> The real issue with dynamically typed languages is that their performance sucks
Every time you say something like this it just makes it obvious you have no idea what you're talking about. You can write almost completely typeless, highly performant, c and assembly code, while high level languages with advanced type systems are generally not the most performant.
You seen to be confused about interpreted/jit/compiled languages and static/dynamic typing - which are not the same thing.
The key points are as follows:
* Development in Dynamically Typed Languages is faster
* Dynamically typed languages use less lines of code than statically typed languages by a significant margin
* The level of bugs is the same between Dynamically typed and Statically typed code.
"You can write almost completely typeless, highly performant, c and assembly code,"
Yes, I'm sure the LOAD instructions take pictures of cats as operands via their typeless instruction sets... What in earth are you on???
"completely typeless, highly performant, c"
well once someone does that let me know. The only thing near is Javascript and that is only faster for microbenchmarks not real programs.
From one of the comments:
https://dev.to/aussieguy/the-non-broken-promise-of-static-ty...
> The article covers a study of the same name. In it, researchers looked at 400 fixed bugs in JavaScript projects hosted on GitHub. For each bug, the researchers tried to see if adding type annotations (using TypeScript and Flow) would detect the bug. The results? A substantial 15% of bugs could be detected using type annotations. With this reduction in bugs, it's hard to deny the value of static typing.
> Yes, I'm sure the LOAD instructions take pictures of cats as operands via their typeless instruction sets... What in earth are you on??
Have you written any assembly? Assembly generally has no or very rudimentary type checking, you're generally dealing with words/bytes and addresses, you can arithmetically add parts of strings, divide pointers, etc. Errors due to these operation will surface at runtime, not be typechecked.
> well once someone does that let me know.
You can use void pointers as return types and arguments for all functions in c code. The effect is significantly less type checking while having equivalent performance.
Actually, that makes it really easy to deny the value of static typing. If the total number of bugs in dynamic and static code is the same. But some bugs in dynamic code would be caught by static typing checking.
We most conclude that adding static typing results in a large number of non-typing related bugs being added to the code base. It's simple maths.
"Have you written any assembly?" Yes, I'm an emulator author, thank you very much.
The registers and opcodes are typed with things such as u8, u16, u32, u64, i32, i64 and only work with data of the right type.
"arithmetically add parts of strings, divide pointers" You mean standard C stuff, you know the statically typed language.
"You can use void pointers as return types and arguments for all functions in c code" Dynamic types is not the same thing as type eraser. That void pointer doesn't carry the information that it points to a picture of a cat for example.
The fact you don't understand the difference between a void pointer and dynamic typing doesn't exactly surprize me. It's more like a giant vtable.
Completely baseless assumption.
> Yes, I'm an emulator author, thank you very much.
Ahahaha let's have a link then.
> The registers and opcodes are typed with things such as u8, u16, u32, u64, i32, i64 and only work with data of the right type.
Those are sizes, not types, and the same opcode generally applies to signed and unsigned integers. You consider that to be a static type system and you think the purpose is performance and not correctness? Lol
> You mean standard C stuff, you know the statically typed language.
You're trying to debate against the need for static typing by pointing out unsafe parts of c? Ahaha
> That void pointer doesn't carry the information that it points to a picture of a cat for example.
First of all you can totally carry around runtime type info and value with a single void pointer. Not to mention many dynamically typed languages have type erasure and many statically typed languages have runtime type info. Also, you've claimed multiple times that there's no need for type checking whatsoever. You need runtime type information at runtime now?