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Ruby/Resistor Colors: Add Mentor Notes #853

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Mar 10, 2019
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Ruby/Resistor Colors: Add Mentor Notes #853

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Ruby/Resistor Colors: Add Mentor Notes
emcoding Mar 10, 2019
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Add `freeze` talking point
emcoding Mar 10, 2019
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33 changes: 33 additions & 0 deletions tracks/ruby/exercises/resistor-colors/mentoring.md
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Resistor Colors is a side exercise, unlocked by Hello World

### New Concepts
Array, Array#index, `map`, Constant, chaining methods
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Add blank line between header and content, following default markdownlint


### Minimal solution for approval
```ruby

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I suggest removing the whitespace above class, but adding an empty line below the header, following default markdownlint.

class ResistorColors

COLOR_CODES = ["black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "grey", "white"]
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Suggested change
COLOR_CODES = ["black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "grey", "white"]
COLOR_CODES = %w[black brown red orange yellow green blue violet grey white].freeze

Default style via rubocop WordArray and rubocop MutableConstant.

Add below this solution that:

  • "Alternatives include writing out the array using brackets"; the talking points already mention this.
  • freeze should only be a talking point but not a reason to disapprove


def self.value(colors)
colors.map { |color| COLOR_CODES.index(color) }.join.to_i
end

end

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Remove whitespace between final end and end of code block.

```

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Add note about acceptable variations include using a module, class << self, module_function and the likes. We don't want mentors to comment on any of that, seeing it's such an early exercise!

### General
This is the very first Array exercise, and the first loop. Introducing `map` is key in this exercise.
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@pgaspar pgaspar Mar 10, 2019 •
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This is the very first Array exercise

Isn't this set up as a bonus exercise? (reference)


### Talking points
- _`%w` notation_: for arrays of strings. Link to [styleguide](https://github.com/rubocop-hq/ruby-style-guide#percent-w)
- _chaining methods_ after a block (especially when people use a local variable for `join.to_i`
- _`each` vs `map`_: this explains the difference: [each vs map](https://learn.onemonth.com/ruby-tutorial-map-vs-each/)
- _variable vs constant_: this article explains just that: [var vs constant](https://ruby-doc.org/docs/ruby-doc-bundle/Tutorial/part_01/variables.html)
- _freeze_: this post has exactly the right level of information: [freeze](https://freelancing-gods.com/2017/07/27/an-introduction-to-frozen-string-literals.html); no need to dive deeper into (im)mutability.


### Changelog
First introduced 2019 Mar 10
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Maybe we should have a specific format for the changelog. Maybe something like:

  • Version 1: exercise first introduced on March 10, 2019

Maybe HighScores can be a good guide as well?