Add unit for adding elements to Arrays

Author: paulgoetze

4_Arrays/3_Adding_elements/solution.rb

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+baggage = ['shirt']
+baggage.unshift('glasses')
+baggage.push('shoes')
+baggage.insert(2, 'trousers', 'socks')
+
+# baggage
+# => ["glasses", "shirt", "trousers", "socks", "shoes"]

4_Arrays/3_Adding_elements/solution_spec.rb

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+require 'rspec'
+require 'code_breaker'
+
+describe 'Your code' do
+  [['solution::code']]
+
+  VARIABLE = :baggage
+  ITEMS    = ['glasses', 'shirt', 'trousers', 'socks', 'shoes']
+
+  it 'defines a variable with name "baggage"' do
+    expect(local_variables.include?(VARIABLE)).to be true
+  end
+
+  if local_variables.include?(VARIABLE)
+    it 'defines a variables "baggage" that has all the items' do
+      expect(eval(VARIABLE.to_s)).to eq ITEMS
+    end
+
+    if eval(VARIABLE.to_s) == ITEMS
+      before(:all) do
+        @statements = CodeBreaker.parse( %q{ [['solution::code']] })
+      end
+
+      it 'uses the unshift method to add "glasses"' do
+        unshift = [{ lvar: VARIABLE }, :unshift, String]
+        expect(@statements.include?(unshift)).to be true
+      end
+
+      it 'uses the push or << method to add "shoes"' do
+        push = [{ lvar: VARIABLE }, :push, String]
+        arrows = [{ lvar: VARIABLE }, :<<, String]
+
+        includes_code = @statements.include?(push) || @statements.include?(arrows)
+        expect(includes_code).to be true
+      end
+
+      it 'uses the insert method to add "trousers" and "socks"' do
+        insert = [{ lvar: VARIABLE }, :insert, Fixnum, String, String]
+        expect(@statements.include?(insert)).to be true
+      end
+    end
+  end
+end

4_Arrays/3_Adding_elements/task.md

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+# Adding elements to Arrays
+
+---
+
+*You will learn:*
+- how to add elements to the end of an Array
+- how to add elements to the beginning of an Array
+- how to add elements at a specific index to an Array
+
+---
+
+If you deal with an Array you will hardly just take the Array as is, but you likely want
+to process and modify it or build new Arrays out of it.
+
+This unit will look into different ways of adding elements to an Array.
+
+## Adding elements to the end of an Array
+
+An Array instance has several methods for adding elements.
+If you want to add a *single* element to the end you can use the `<<` method:
+
+`  numbers = [1, 2, 3]`
+`  numbers << 4`              *# => [1, 2, 3, 4]*
+
+You could also write `numbers.<<(4)`, so the missing *.* and *()* are just a bit of
+syntactical sugar.
+
+A similiar method for adding an element to the end of an Array is `push`:
+
+`  chars = ['a', 'b']`
+`  chars.push('c')`           *# => ['a', 'b', 'c']*
+
+The difference is, that `push` accepts multiple arguments, so that you can add as
+many elements as you want in a single call:
+
+`  chars.push('d', 'e', 'f')` *# => ['a', 'b', 'c', 'd', 'e', 'f']*
+
+Both `<<` and `push` will modify the given Array directly. If you check the values
+of the variables above after calling the methods on them they will contain the added values:
+
+`  numbers`                   *# => [1, 2, 3, 4] *
+`  chars`                     *# => ['a', 'b', 'c', 'd', 'e', 'f']*
+
+If you want to build a new Array out of an existing one by adding elements, the `+` method
+will help you to combine two Arrays:
+
+`  numbers = [1, 2]`
+
+`  more_numbers = numbers + [3]`           *# => [1, 2, 3]*
+`  even_more_numbers = numbers + [-1, -2]` *# => [1, 2, -1, -2]*
+
+The original Array will stay the same:
+
+`  numbers`                   *# => [1, 2]*
+
+## Adding elements to the beginning of an Array
+
+If you want to add elements to the beginning of an Array instead, you can use the
+`unshift` method which takes 1 or more elements to add as arguments:
+
+`  numbers = [1, 2]`
+`  numbers.unshift(0)`        *# => [0, 1, 2]*
+`  numbers.unshift(-2, -1)`   *# => [-2, -1, 0, 1, 2]*
+
+Similar to `push`, the `unshift` method will modify the original Array.
+
+## Addding elements at a certain index
+
+If adding an element to the end or the beginning of an Array is not what you want,
+then there is an `insert` method, that allows you to insert one or more elements
+at a defined position:
+
+`  vegetables = ['potato', 'pepper']`
+`  vegetables.insert(1, 'cucumber', 'cauliflower')`
+
+The first argument is the index where to insert the first element (keep in mind, that
+the indexing starts at 0, so *1* means: “Insert before the second element”).
+
+Like `<<` and `push`, `insert` also modifies the original Array, so that *vegetables* holds
+all the values now:
+
+`  vegetables` *# => ['potato', 'cucumber', 'cauliflower', 'pepper']
+
+Now that you have learned a couple of possibilities for adding elements to an Array
+let’s summarize them again:
+
+`  <<`      *adds element at end           modifies the original Array*
+`  push`    *adds elements at end          modifies the original Array*
+`  +`       *adds elements at end          creates a new Array*
+`  unshift` *adds elements at beginning    modifies the original Array*
+`  insert`  *adds elements at given index  modifies the original Array*
+
+---
+
+Prepare a case with some things for a trip:
+
+Create a variable *baggage* holding an Array with one element *"shirt"*.
+Add a pair of *"glasses"* before the shirt and some *"shoes"* after the shirt.
+Then add another *"trousers"* and a pair of *"socks"* before the shoes.
+
+---