Add hash concept and exercise #1809

meatball133 · 2025-12-31T16:55:50Z

This is apart of making ostruct an optional concept: https://forum.exercism.org/t/openstruct-is-now-officially-discouraged/17490

meatball133 · 2025-12-31T17:08:14Z

I would say we are a bit in a limbo, though, the array and enumeration concepts are connected to one exercise, and personally, I think it makes sense to introduce arrays before hashes. But the enumeration concept mentions hashes. So either I think enumeration should be stripped out of hashes, which might not make sense. Instead it might make sense to make a separate exercise for arrays so we can have. arrays => hashes => enumeration. I think this shouldn't necessarily hold this pr, since it won't make things worse in my opinion, since not having a hash concept to begin with isnt ideal either.

meatball133 · 2025-12-31T17:08:31Z

An option could be to temporairly place hashes over arrays

kotp · 2026-01-07T21:47:07Z

An option could be to temporairly (sic) place hashes over arrays

I do tend to teach "collections" rather than independent data structures, since other than the data structure itself, the idea of Enumerable being the thing that gives a lot of power. What do you think about taking that approach for a concept, rather than the concept of "map/dictionary" specifically? I have not looked at the changes in this PR yet, though. Just got back to my computer after a two week break (travelling).

kotp · 2026-01-07T21:48:30Z

concepts/hashes/about.md

+
+Even though hashes are unordered collections, Ruby maintains the insertion order of key-value pairs.
+This means that when you iterate over a hash, the pairs will be returned in the order they were added.
+However, deleting elements may affect the order of remaining elements.


Expand on this, is the order at that point of operation undeterminate? Citation would be helpful for further exploration, and historically in Ruby, this is an interesting point as well.

kotp · 2026-01-07T21:49:24Z

concepts/hashes/about.md

+my_hash = { 1 => "one", :two => 2, "three" => [3, "three"] }
+```
+
+Alternatively if the keys are symbols, you can use a more JSON-style syntax:


Perhaps avoid JSON reference. But maybe mention the "newer syntax as of Ruby 1.9" form as shown.

kotp · 2026-01-07T21:50:47Z

concepts/hashes/about.md

+my_hash = { name: "Alice", age: 30, city: "New York" }
+```
+
+You can create an empty hash using the `Hash.new` method:


Capitalize "Hash" when speaking of the type specifically or the object itself, since hash is also a method and an idea. (Even if it weren't this situation, I would likely suggest capitalization as well as code syntax for the specific thing.)

kotp · 2026-01-07T21:51:29Z

concepts/hashes/about.md

+
+## Accessing values
+
+You can access values in a hash using their corresponding keys, the syntax reminds of array indexing, but using the key instead of an index:


Suggested change

You can access values in a hash using their corresponding keys, the syntax reminds of array indexing, but using the key instead of an index:

You can access values in a `Hash` instance using its corresponding keys, the syntax reminds of array indexing, but using the key instead of an index:

kotp · 2026-01-07T21:54:50Z

concepts/hashes/about.md

+You can access values in a hash using their corresponding keys, the syntax reminds of array indexing, but using the key instead of an index:
+
+```ruby
+my_hash = { "name" => "Alice", "age" => 30, "city" => "New York" }


No space inside Hash delimiters, similar to Array and Range, save the space inside {} delimiters for blocks.

Suggested change

my_hash = { "name" => "Alice", "age" => 30, "city" => "New York" }

my_hash = {"name" => "Alice", "age" => 30, "city" => "New York"}

Alternatively, present it as:

Suggested change

my_hash = { "name" => "Alice", "age" => 30, "city" => "New York" }

my_hash = {

"name" => "Alice",

"age" => 30,

"city" => "New York"

}

Indentation adjusted for readability (this is how I style my key/value pairs reducing eye jitter), and not necessary, but might be nice to have.

kotp · 2026-01-07T22:58:03Z

exercises/concept/gross-store/.meta/exemplar.rb

@@ -0,0 +1,38 @@
+class GrossStore
+  UNITS = {'quarter_of_a_dozen' => 3, 'half_of_a_dozen' => 6, 'dozen' => 12, 'small_gross' => 120, 'gross' => 144, 'great_gross' => 1728}.freeze


Nice that there is no space inside the delimiter, but why the freeze? We advertise this as a mutable object, but then make it immutable here?

Also blank line after class definition line is a signal of "topic change" and creates a paragraph of sorts.

This is an exemplar, not just an example, so we should apply opinions here to be that exemplar.

But I will not critique explicitly here. Welcome to discuss it on Discord, though, if you want to (even pair program through it if you want).

Or even as a product of a mentor request! ;)

kotp · 2026-01-07T23:00:08Z

exercises/concept/gross-store/gross_store.rb

@@ -0,0 +1,24 @@
+class GrossStore
+  UNITS = { 'quarter_of_a_dozen' => 3, 'half_of_a_dozen' => 6, 'dozen' => 12, 'small_gross' => 120, 'gross' => 144,


Suggested change

UNITS = { 'quarter_of_a_dozen' => 3, 'half_of_a_dozen' => 6, 'dozen' => 12, 'small_gross' => 120, 'gross' => 144,

UNITS = {'quarter_of_a_dozen' => 3, 'half_of_a_dozen' => 6, 'dozen' => 12, 'small_gross' => 120, 'gross' => 144,

As a minimum, no space inside delimiters.

Perhaps a columnar presentation of the Hash as well, easier to see patterns, etc., than having a horizontal showing of this.

kotp · 2026-01-07T23:01:11Z

exercises/concept/gross-store/gross_store.rb

+  UNITS = { 'quarter_of_a_dozen' => 3, 'half_of_a_dozen' => 6, 'dozen' => 12, 'small_gross' => 120, 'gross' => 144,
+            'great_gross' => 1728 }.freeze
+
+  attr_reader :bill


public method definition above the private method initialize is something that I personally detest, it suggests something that is untrue (that initialize is perhaps not private, since in this organization it is in the midst of public method definitions.

kotp · 2026-01-07T23:02:11Z

config.json

        ],
        "prerequisites": [
-          "advanced-enumeration"
+          "hashes"


This should be capitalized, as hashes are created by using hash method calls, and is something different.

This is the slug

kotp · 2026-01-07T23:02:24Z

config.json

        ],
        "prerequisites": [
-          "ostruct"
+          "hashes"


... same here.

meatball133 · 2026-01-08T20:29:23Z

I do tend to teach "collections" rather than independent data structures, since other than the data structure itself, the idea of Enumerable being the thing that gives a lot of power. What do you think about taking that approach for a concept, rather than the concept of "map/dictionary" specifically? I have not looked at the changes in this PR yet, though. Just got back to my computer after a two week break (travelling).

I think in a way that is a good idea, I think however that the concept might end up being too big. Since this concept is around 200 lines say array is the same and then what about other collections (such as sets). It might make sense to have these after each other but don't know about having a single big one.

Add introduction and about sections for hashes

c268be8

meatball133 force-pushed the add-hashes branch 2 times, most recently from 88c383c to c4876ae Compare December 31, 2025 17:00

Add concept and exercise

d89a432

meatball133 force-pushed the add-hashes branch from c4876ae to d89a432 Compare December 31, 2025 17:02

kotp requested changes Jan 7, 2026

View reviewed changes


		## Accessing values

		You can access values in a hash using their corresponding keys, the syntax reminds of array indexing, but using the key instead of an index:

	You can access values in a hash using their corresponding keys, the syntax reminds of array indexing, but using the key instead of an index:
	You can access values in a `Hash` instance using its corresponding keys, the syntax reminds of array indexing, but using the key instead of an index:

	my_hash = { "name" => "Alice", "age" => 30, "city" => "New York" }
	my_hash = {"name" => "Alice", "age" => 30, "city" => "New York"}

		@@ -0,0 +1,38 @@
		class GrossStore
		UNITS = {'quarter_of_a_dozen' => 3, 'half_of_a_dozen' => 6, 'dozen' => 12, 'small_gross' => 120, 'gross' => 144, 'great_gross' => 1728}.freeze

		@@ -0,0 +1,24 @@
		class GrossStore
		UNITS = { 'quarter_of_a_dozen' => 3, 'half_of_a_dozen' => 6, 'dozen' => 12, 'small_gross' => 120, 'gross' => 144,

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meatball133 commented Dec 31, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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meatball133 commented Jan 8, 2026

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meatball133 commented Dec 31, 2025 •

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