Comment by DonaldPShimoda 2 days ago
This is a really minor point, but "strongly typed" and "statically typed" are not interchangeable terms. In the context of your comments here, you are exclusively interested in the static nature of the type system, rather than anything about the "strength" of it (which is something totally different and inconsistently defined).
Can you explain more about strongly typed vs statically typed?
Typically, "static typing" refers types being checked at compile time rather than runtime; in other words, the analysis can happen before the program is run, which gives you some degree of confidence in what the behavior will be when actually running it. The opposite of this is "dynamic typing", which means that the type-checking happens while the program is running, so you don't have the up-front guarantee that you won't end up having an error due to the wrong type being used somewhere. In practice, this isn't a strict binary where a language has to be 100% static or 100% dynamic. For example, Java is mostly statically typed, but there are some cases where things are a bit more dynamic (e.g the compiler allowing certain casts that might not end up being successful at runtime, at which point they throw an exception). On the other hand, Python traditionally has been a dynamically typed language, but in recent years there have various efforts to allow type annotations that allow checking some things in advance, which moves it a bit in the static direction (I'm not familiar enough with the current state of things in the ecosystem to have any insight into how much this has moved the needle).
On the other hand, "strong typing" isn't as quite as standardized in type systems terminology, but broadly speaking, it tends to be used to describe things like how "sound" a type system is (which is a well-defined concept in type systems theory), whether or not implicit type coercions can occur in the language, or other things that roughly translate to whether or not its possible for things to get misused as the wrong type without an explicit error occurring. Two examples that are commonly cited are JavaScript[0], with its sometimes confusion implicit conversions to allow things like adding an empty object and an empty array and getting the number 0 as the result (but not if added in the other order!) and C, with it being possible to interpret a value as whatever the equivalent underlying bytes would represent in an arbitrary type depending on the context its used.
[0]: I normally don't like to link to videos, but this famous comedic talk demonstrating a few of these JavaScript quirks is so thoroughly entertaining to watch again every few years that I feel like it's worth it so that those who haven't seen it before get a chance: https://www.destroyallsoftware.com/talks/wat
> static typing: 2 + "2" does not compile/parse (e.g. Python vs mypy, Typescript vs JS)
I think this example is not correct, because static typing doesn’t affect how values of different types interact. And while I don’t know of any staticly typed language where specifically `2 + “2”` is a valid expression, statically typed languages definitely can be weakly typed: the most prominent example is C where one can combine values of different types without explicitly converting them to the same type (`2 + 2.0`).
I believe strong/weak and static/dynamic are orthogonal. And my examples are:
- Strong: `2 + “2”` is a error,
- Weak: `2 + “2”` makes 4 (or something else, see the language spec),
- Static: `var x = 2; x = “2”` is an error,
- Dynamic: `var x = 2; x = “2”` is fine.
Dynamic typing can forbid the latter (at runtime), but it's implementation dependent. There's a further distinction, Latent typing, which is where types are associated with values rather than variables.
But a dynamic language can have types associated with variables, and it can forbid changing those types after their types have been checked the first time.
could also be "4" or 4! 4 seems like it would be the most evil option, honestly
You are absolutely right. Thanks for pointing it out.