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[New concept + exercise]: Case (#1595)
* Add case concept + exercise * Add new line in end of exemplar * Fix * Add missing spacing * Fixes based on feedback * remove trailing whitespace * Add contributor to config.json file --------- Co-authored-by: Victor Goff <[email protected]>
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‎concepts/case/.meta/config.json

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{
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"blurb": "Case is a form of control expression, and allows for writing large readable if-else-if statements.",
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"authors": ["meatball133"],
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"contributors": ["kotp"]
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}

‎concepts/case/about.md

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# Case
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[Case][case] (often referred to as switch in other languages) is a form of control expression like if-else.
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Case allows for chaining of multiple if-else-if statements and can be more readable while still providing flow control.
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A case is defined by the keyword `case` followed by an optional expression.
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Then for each case, the keyword `when` is used followed by an expression which is compared to the case expression.
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The `when` keyword should not be indented from the `case` keyword.
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After the `when` keyword is the code that should be executed if the case expression matches the when expression.
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Case allows for an optional `else` statement which is executed if no other case matches.
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The case expression is evaluated and then compared to each `when` expression.
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The expression is compared using the case equality operator (`===`).
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```ruby
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value = 1
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case value
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when 1
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"One"
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when 2
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"Two"
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else
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"Other"
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end
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# This is the same as:
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value = 1
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if 1 === value
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"One"
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elsif 2 === value
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"Two"
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else
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"Other"
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end
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```
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## Case equality operator (`===`)
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The case equality operator (`===`) is a bit different from the equality operator (`==`).
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The operator checks if the right side is a member of the set described by the left side.
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This means that it does matter where each operand is placed.
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How this works depends on the type of the left side, for example a `Range` would check if the right side is in the range or a `Object` would check if the right side is an instance of the `Object`.
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```ruby
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(1..3) == 1 # => false
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(1..3) === 1 # => true
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String == "foo" # => false
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String === "foo" # => true
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```
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## Case with multiple expressions
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Cases allow for matching multiple expressions in a single case with each possible value separated by a comma.
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It will execute the code if any of the expressions match.
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This can be useful when you want a single case to have multiple possible values.
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```ruby
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case var
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when 1, 2
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"One or two"
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else
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"Other"
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end
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```
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## Cases with ranges
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Cases can also check if a value is in a range.
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This is done by having a range as the when expression.
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```ruby
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case var
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when 1..3
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puts "One to three"
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else
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puts "Other"
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end
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```
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## Cases with no case expression
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When there is no need for a case expression, it is possible to omit it.
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Doing this will make it so that each case expression is evaluated for truthiness.
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And makes them behave like if-else-if statements.
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```ruby
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case
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when 1 == 1
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"One is equal to one"
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when 1 > 2
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"One is greater than two"
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else
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"Other"
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end
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```
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## Single line when
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Ruby allows for single line case statements.
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This can be used when you have a simple single line statement.
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The single line when statement is written as `when <expression> then <statement>`.
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And when used in the else statement it is written as `else <statement>`.
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```ruby
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case var
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when 1 then "One"
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when 2 then "Two"
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else "Other"
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end
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```
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## Case with types
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Case allows for the matching with types.
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This is useful when wanting different behavior depending on the type of a variable.
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```ruby
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case var
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when Integer
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"Integer"
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when String
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"String"
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else
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"Other"
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end
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```
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[case]: https://www.rubyguides.com/2015/10/ruby-case/

‎concepts/case/introduction.md

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# Case
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[Case][case] (often referred to as switch in other languages) is a form of control expression like if-else.
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Case allows for chaining of multiple if-else-if statements and can be more readable while still providing flow control.
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A case is defined by the keyword `case` followed by an optional expression.
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Then for each case, the keyword `when` is used followed by an expression which is compared to the case expression.
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The `when` keyword should not be indented from the `case` keyword.
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After the `when` keyword is the code that should be executed if the case expression matches the when expression.
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Case allows for an optional `else` statement which is executed if no other case matches.
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The case expression is evaluated and then compared to each `when` expression.
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The expression is compared using the case equality operator (`===`).
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```ruby
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value = 1
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case value
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when 1
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"One"
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when 2
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"Two"
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else
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"Other"
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end
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# This is the same as:
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value = 1
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if 1 === value
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"One"
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elsif 2 === value
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"Two"
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else
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"Other"
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end
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```
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## Case equality operator (`===`)
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The case equality operator (`===`) is a bit different from the equality operator (`==`).
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The operator checks if the right side is a member of the set described by the left side.
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This means that it does matter where each operand is placed.
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How this works depends on the type of the left side, for example a `Range` would check if the right side is in the range or a `Object` would check if the right side is an instance of the `Object`.
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```ruby
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(1..3) == 1 # => false
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(1..3) === 1 # => true
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String == "foo" # => false
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String === "foo" # => true
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```
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## Case with multiple expressions
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Cases allow for matching multiple expressions in a single case with each possible value separated by a comma.
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It will execute the code if any of the expressions match.
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This can be useful when you want a single case to have multiple possible values.
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```ruby
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case var
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when 1, 2
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"One or two"
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else
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"Other"
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end
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```
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## Cases with ranges
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Cases can also check if a value is in a range.
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This is done by having a range as the when expression.
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```ruby
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case var
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when 1..3
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puts "One to three"
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else
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puts "Other"
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end
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```
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## Cases with no case expression
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When there is no need for a case expression, it is possible to omit it.
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Doing this will make it so that each case expression is evaluated for truthiness.
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And makes them behave like if-else-if statements.
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```ruby
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case
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when 1 == 1
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"One is equal to one"
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when 1 > 2
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"One is greater than two"
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else
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"Other"
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end
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```
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## Single line when
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Ruby allows for single line case statements.
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This can be used when you have a simple single line statement.
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The single line when statement is written as `when <expression> then <statement>`.
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And when used in the else statement it is written as `else <statement>`.
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```ruby
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case var
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when 1 then "One"
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when 2 then "Two"
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else "Other"
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end
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```
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## Case with types
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Case allows for the matching with types.
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This is useful when wanting different behavior depending on the type of a variable.
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```ruby
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case var
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when Integer
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"Integer"
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when String
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"String"
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else
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"Other"
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end
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```
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[case]: https://www.rubyguides.com/2015/10/ruby-case/

‎concepts/case/links.json

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[
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{
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"url": "https://www.rubyguides.com/2015/10/ruby-case/",
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"description": "Ruby Guides: The Many Uses Of Ruby Case Statements"
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}
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]

‎config.json

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"symbols"
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]
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},
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{
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"slug": "blackjack",
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"name": "BlackJack",
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"uuid": "414ee9b2-c62d-41d5-aa1e-c5d82fb8562c",
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"concepts": [
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"case"
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],
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"prerequisites": [
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"ranges",
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"modules"
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]
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},
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{
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"slug": "bird-count",
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"name": "Bird Count",
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"slug": "modules",
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"name": "Modules"
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},
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{
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"uuid": "bcea6b47-4db8-4cce-b341-c2f97182687b",
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"slug": "case",
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"name": "Case"
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},
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{
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"uuid": "ad546bc1-7583-482d-9159-44e08c50c7b8",
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"slug": "exceptions",

‎exercises/concept/blackjack/.docs/hints.md

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# Hints
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## 1. Calculate the value of any given card.
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- The `Blackjack.parse_card` method should take a string (e.g. `"ace"`) and return its value (e.g. 11).
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- Define a [`case` statement][case] and assign the value of the card as the case's value.
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- King, Queen, Jack and 10 can be handled with a single case.
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- The `case` can have an `else` case.
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In any case the function should return `0` for unknown cards.
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## 2. Name ranges of values.
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- Compute the player score by adding up the values of the two player cards.
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- Define a [`case` statement][case] and assign the name of the range as the case's value.
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- The switch can use [`Range`][range] objects as cases to check if a value is in a range.
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## 3. Implement the decision logic for the first turn.
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- Compute the player score by adding up the values of the two player cards.
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- You can either use a big [`case` statement][case] on the player
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score (maybe with nested `if`-statements on the dealer-score in some cases),
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- or you could distinguish separate player score categories (say "small hands"
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with a score less than 12, "medium hands" with a score in the range 12..20 and
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"large hands" with a score greater than 20) and write separate functions for
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all (or some) of these categories.
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[case]: https://www.rubyguides.com/2015/10/ruby-case/
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[range]: https://rubyapi.org/o/range

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