[pansa2]

> There are many expressions you can write in dynamically typed languages that don’t make any sense, probably most of them actually, but they have to be considered valid because it’s a dynamically typed language.

Not really - a language could throw an exception in these cases, as Python does for things like “a”+1. Not every dynamically-typed language is JavaScript.

[mantap]

That is the difference between a dynamically typed language (like Python) and an untyped language (like JS). The dynamically typed language checks types at runtime, whereas the untyped language doesn't.

[simias]

JS is not "untyped". It literally has a "typeof" operator. You probably mean strongly vs. weakly typed. JS is dynamically, rather weakly typed. Python is dynamically, strong-ish-ly typed. C is statically, weakly typed. Rust is statically, strongly type.

Those two attributes are mostly orthogonal.

[mantap]

There's no such thing as "strongly" or "weakly" typed languages. Those terms have no definition and are meaningless. Yes Wikipedia will tell you that C and JS are weakly typed, but what attribute is it that C and JS's type systems share? They share absolutely nothing in common.

Dynamic typing refers to checking of types at runtime. JS does not do this consistently or effectively. Python does.

The typeof operator cannot be the basis of a type system since you can count all the answers it gives on your fingers. JS needs a bunch of extra functions like Array.isArray() to determine if something is an array or not. The language itself has no clue, everything that isn't a primitive is just an "object" as far as JS is concerned.

[simias]

"Strongly" and "weakly" typed is not a binary attribute of a language and there's a gradient so languages can be more or less strongly or weakly typed but I think those are still useful qualifiers. C lets you add ints and doubles without explicit cast, Rust doesn't. Rust is more strongly typed than C. It's not meaningless to say that. A metric being partially relative or interpretative doesn't make it useless.

For the rest I don't understand how anybody can seriously make the argument that JS has no types. Shell scripts have no types because almost everything is a character string and that's it. JS type system is very limited but it does exist and I don't see how it can be used to justify {} + [] = 0, which is where we started (especially given that {} and [] are objects in JS, but 0 is a "number", so different core types). Adding two objects and getting a number is not a limitation of the type system, it's a conscious decision by the designers (or at least the side effect of one).

[pmontra]

Python (and Ruby) are dynamically typed and strong typed. They are two different things. Strong typed doesn't mean that you can't do this

  a = "a"
  a = 1

That's dynamic typing. Strong typing means only that

  a = "a" + 1

fails.

More about that at https://en.hexlet.io/courses/intro_to_programming/lessons/ty...

JavaScript and PHP and Perl automatically cast to a reasonable value with all the advantages and pitfalls.

[dorgo]

>Strong typing means only that

> a = "a" + 1

>fails.

String a = "a" + 1; works in Java. So Java is not strongly typed?

[angus_gh]

In some ways yes, Java is not so strongly typed; a statically-typed language can be weakly typed.

See C where ints, pointers, floats, and bools can almost all coerce into each other, such that the compiler will allow you to use arithmetic/logic operators with most different types, whether you meant to or not.

[sah2ed]

That’s because the language designers overloaded the arithmetic operator (+) to perform string concatenation when the operands can be cast as Strings.

Without overloading the + operator, string concatenation which is a common operation, would have been unnecessarily verbose. Your example without the + operator would look like below:

   String a = new String(“a”).concat(1); // String object concat
   String a = “a”.concat(1);             // String literal concat

[jakear]

The same could be said of JS but for some reason it gets shit but Java gets off Scott-free.

[zapzupnz]

Java doesn't get off scot-free for anything; nobody likes it, they just use it because they must.

Java just happens to be less prominent in tech media right now since JS on the server is the new(-ish) hotness. There's still plenty of dislike for it, but really, all that needed saying about it happened long before now.

[shrimpx]

It’s really not dynamic vs untyped, but the extent to which the language design chooses to coerce a value into a given type instead of raising a runtime type error. Python is guilty of this too with its truthy values, e.g. `if []` — an empty list of type `list` is suddenly apparently inhabiting the bool type and is equivalent to False.