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Nested Collections: "immutable" arrays, Clarify independence of inner arrays in nested collections example #30215

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Merged
merged 4 commits into from
Oct 11, 2025
Merged

Nested Collections: "immutable" arrays, Clarify independence of inner arrays in nested collections example #30215

merged 4 commits into from
Oct 11, 2025

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@Bijay-Shre-stha
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@Bijay-Shre-stha Bijay-Shre-stha commented Oct 6, 2025

Because

The lesson currently uses the term immutable incorrectly. The example:

immutable = Array.new(3) { Array.new(2) }
creates an array that can clearly be changed:
immutable[0][0] = 1000
immutable << "new element"

This might confuse students coming from other languages where “immutable” has a stricter meaning. A clearer description would help avoid misunderstanding.

This PR

  • Updates the description of the example to avoid using the word “immutable.”
  • Clarifies that the array contains references to separate objects (nested arrays) which can be independently modified.
  • Adds an explanation about the difference between using { Array.new(2) } vs Array.new(3, Array.new(2)).

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Pull Request Requirements

  • I have thoroughly read and understand The Odin Project curriculum contributing guide
  • The title of this PR follows the location of change: brief description of change format, e.g. Intro to HTML and CSS lesson: Fix link text
  • The Because section summarizes the reason for this PR
  • The This PR section has a bullet point list describing the changes in this PR
  • If this PR addresses an open issue, it is linked in the Issue section
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  • If any lesson files are included in this PR, they follow the Layout Style Guide

@github-actions github-actions bot added the Content: Ruby Involves the Ruby course label Oct 6, 2025
@Bijay-Shre-stha Bijay-Shre-stha mentioned this pull request Oct 6, 2025
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@oz123
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oz123 commented Oct 7, 2025

The explicit explanation is indeed a welcome addition. I'd still give a few more minutes on how to avoid using the word immutable in the paragraph above it.

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Bijay-Shre-stha commented Oct 7, 2025

@oz123 so that i can make it nested_arrays? so that i can be more simpler to understand?

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oz123 commented Oct 7, 2025 •
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I was referring to the paragraph that starts with:

To create an immutable array of mutable objects ...

This feels very confusing for me. This example :

mutable = Array.new(3, Array.new(2))
#=> [[nil, nil], [nil, nil], [nil, nil]]
mutable[0][0] = 1000
#=> 1000
mutable
#=> [[1000, nil], [1000, nil], [1000, nil]]

I think this should not be termed "mutable" but as "caution" this syntax is not doing what you expect.

I would first show the "correct" way to create the collection:

nested = Array.new(3) { Array.new(2) }

And than add a caution block that shows what happens with the syntax:

mutable = Array.new(3, Array.new(2))

Thank you for your effort on this.

JoshDevHub
JoshDevHub requested changes Oct 8, 2025
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This is a good idea. Also for clarity, when you say

This might confuse students coming from other languages where “immutable” has a stricter meaning.

It also has a strict meaning in the Ruby language. The example given in the lesson is just incorrect with its use of mutable/immutable

Anyways, before I approve, I think the example given above your changes should be altered as well. The line that says:

To create an immutable array of mutable objects (string, array, hash, etc), you will need to pass the default value for Array.new via a block, using curly braces, instead of the second optional argument.

Probably needs to be something like this (omitting the incorrect 'immutable' word):

To correctly create an array of mutable objects (string, array, hash, etc), you will need to pass the default value for Array.new via a block, using curly braces, instead of the second optional argument.

The variable name in the example below that could probably be changed to nested_array as well instead of mutable.

How do these changes sound?

@Bijay-Shre-stha
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Bijay-Shre-stha commented Oct 9, 2025

@JoshDevHub i have change its to nested_arrays, could you verified it once #30215

oz123
oz123 reviewed Oct 9, 2025
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Bijay-Shre-stha commented Oct 9, 2025

@JoshDevHub, updated PR. #30215

oz123
oz123 reviewed Oct 9, 2025
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@Bijay-Shre-stha Bijay-Shre-stha requested a review from oz123 October 9, 2025 11:55
oz123
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That is better.

@JoshDevHub JoshDevHub merged commit 05733e5 into TheOdinProject:main Oct 11, 2025
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