Discussion on: JavaScript, Ruby and C are not call by reference

[Iduoad]

This actually was a semester long discussion with a professor of mine 😁.

Here is how I think of it:

Functions are borowed from maths, and in maths functions always copy !

Let's consider the following real function: R->R, f:x->x²
with a=4 if we evaluate f(a)=16 the variable a will still be equal to 4.

In programming(To be clear in most programming languages[1]) functions always copy their arguments, then work the copy. i.e functions are passing_by_value creatures, they always copy what they got, and it's what they copy ("reference type" or "value type") which define if they will act on the state or not.

As @Valentin_Baca pointed out Java behave in the same way, python too :

def by_value(ob):
    ob = []

def by_reference(ob):
    ob.append(11)

li = [0]*4
print(li) #[0,0,0,0]
by_value(li)
print(li) #[0,0,0,0]
by_reference(li)
print(li) #[0,0,0,0,11]

1: python is an exception, it has mutables and immutables and it passes arguments to functions by assigning them.

Please correct me if I'm wrong

[Derk-Jan Karrenbeld]

Valentin made a good comment and jmc went into more detail.

Valentin Baca

Full-stack software engineer & tech lead. 8y industry xp, primarily at Amazon.com Currently on AmazonSmile. My posts are my own opinions and do not reflect my employee's opinion.

val_baca valbaca

jmc

Full stack web dev. Studying FP web development approaches, while helping Mission Bit create paths to programming for underserved public school kids. Previously @ Gradescope.

johncip http://github.com/johncip/

Python isn't really an exception, but yes, I understand what you're saying. Looking through the python source code, it seems again that it is mostly what we are trying to say when no reference is copied. The re-assignment in python is actually copying a reference, but indeed, no new memory need be allocated, for that reference -- sorta, because the identifier (name) still needs to live... inside the memory.

So even though Python doesn't "copy" the reference like JavaScript does (create a new JSVal that points to the same object), it does so on a waaaay lower level (point directly to the original same object).

Ugh. It's giving me a slight headache 😅😅😅.

However, there are actually quite a few (mostly older) languages that don't copy at all, which would be those languages that are not call by value/sharing/object :).

The most interesting to me are copy-restore languages or those theoretical ones that only copy on write... a topic for another time.