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0 pointspansa26y ago0 comments

> 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.

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6 comments · 1 top-level

mantap6y ago· 5 in thread

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.

simias6y ago

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.

mantap6y ago

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.

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pmontra6y ago

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.

dorgo6y ago

>Strong typing means only that

> a = "a" + 1

>fails.

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

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shrimpx6y ago

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.

j / k navigate · click thread line to collapse

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