Is it worth introducing `copy()` into learnxiny?

New to Julia
1

Many new users use: Learn Julia in Y Minutes
New users coming from Matlab/Octave (like myself) may not realize that using = w/ arrays does not create a new copy.

a1 = [1:5;]
a2 = a1
a2[5] = a2[5] +40
a2 
a1
#
a1 = [1:5;]
a2 = copy(a1)
a2[5] = a2[5] +40
a2 
a1

This is @ChrisRackauckas Gotcha #5: Views, Copy, and Deepcopy

Is this worth adding?

2 Likes
2

Sure–it’s an important part of Julia, but it’s probably worth being clear that this has nothing to do with arrays in particular; rather it is a property of how = works with everything in Julia. In fairness, though, new users will often first experience this in the context of an array just because they are so widely used.

Something like:

# Assignment with `=` attaches a new label to the same value without copying
a = [1, 2, 3]
b = a
# Now `b` and `a` point to the same value, so changing one affects the other:
a[3] = 5
b[3]  # => 5

# The `copy()` function can create a shallow copy of an array, dictionary,
# or other container
a = [1, 2, 3]
c = copy(a)
a[3] = 5
c[3] # => 3

might be a nice addition.

2 Likes
3

Thanks.
Should this go under:

1. Primitive Datatypes and Operators

or

2. Variables and Collections

or somewhere else
I’m reluctant to use my own judgement bc alot of ppl use this tutorial…

4

I’d say probably (2), but I’d be interested if other people have opinions too.

5

Put it under (2) for now, else I’ll forget.
Tagged @rdeits & linked to here.
If someone has a better idea, we can improve it later