Add unit for accessing Arrays

Author: paulgoetze

4_Arrays/2_Accessing_elements/solution.rb

@@ -0,0 +1,7 @@
+# e.g.:
+languages = ['Ruby', 'Elixir', 'Scala', 'Erlang', 'OCaml']
+
+first = languages.first
+last = languages.last
+
+some_languages = languages[1..3]

4_Arrays/2_Accessing_elements/solution_spec.rb

@@ -0,0 +1,44 @@
+require 'rspec'
+require 'code_breaker'
+
+VARIABLES = [:languages, :first, :last, :some_languages].freeze
+
+describe 'Your code' do
+  [['solution::code']]
+
+  VARIABLES.each do |name|
+    it "defines a variable with name \"#{name}\"" do
+      expect(local_variables.include?(name)).to be true
+    end
+
+    if local_variables.include?(name)
+      if [:languages, :some_languages].include?(name)
+        it "assigns an Array to the variable \"#{name}\"" do
+          expect(eval(name.to_s)).to be_an_instance_of Array
+        end
+      elsif local_variables.include?(:languages) && name == :first
+        it "assigns the first language to the variable \"#{name}\"" do
+          expect(eval(name.to_s)).to eq languages.first
+        end
+      elsif local_variables.include?(:languages) && name == :last
+        it "assigns the last language to the variable \"#{name}\"" do
+          expect(eval(name.to_s)).to eq languages.last
+        end
+      end
+
+      if name == :languages
+        it "assigns an Array to the variable \"#{name}\" with 5 String elements" do
+          values = Array.new(eval(name.to_s))
+          expect(values.length).to eq 5
+          values.each { |value| expect(value).to be_an_instance_of String }
+        end
+      end
+
+      if local_variables.include?(:languages) && name == :some_languages
+        it "assigns an Array to the variable \"#{name}\" with 5 String elements" do
+          expect(eval(name.to_s)).to eq languages[1..3]
+        end
+      end
+    end
+  end
+end

4_Arrays/2_Accessing_elements/task.md

@@ -0,0 +1,81 @@
+# Accessing elements
+
+---
+
+*You will learn:*
+- how to get single elements from an Array
+- how to get subsets of elements from an Array
+
+---
+
+Each element in an Array is associated with a fixed place – its *index*.
+The index is an Integer which allows to access an element in the Array.
+
+The index 0 points to the first element, the index 1 to the second element, etc.
+Negative indexes point to elements backwards from the last element. E.g. -1 points
+to the last element, -2 points to the second last element, and so on.
+
+## Getting a single element from an Array
+
+You can get the object from an Array at an index by using squared brackets:
+
+`  numbers = [2, 4, 9]` *# defining an Array `numbers`*
+`  numbers[0]`          *# => 2
+`  numbers[1]`          *# => 4
+`  numbers[2]`          *# => 9
+`  numbers[-1]`         *# => 9
+
+If there is no element present for the given index you will get a *nil* value:
+
+`  numbers[3]`          *# => nil
+
+`[]` is just an ordinary method that is defined for an instance of Array.
+
+Another way for getting a single element is using the alias method `at`:
+
+`  numbers.at(0)`       *# => 2
+`  numbers.at(-1)`      *# => 9
+`  numbers.at(3)`       *# => nil
+
+There are two methods for getting special elements of an Array: `first` and `last`.
+`first` – as you might have guessed – returns the first element (at index 0),
+and `last` returns the last element (at index -1):
+
+`  numbers.first`       *# => 2*
+`  numbers.last`        *# => 9*
+
+## Getting a subset of elements from an Array
+
+You can also pass 2 parameters to the `[]` method. This allows to select a subarray
+by defining the index to start at and the number of elements you want to grab, e.g.:
+
+`  numbers[1, 2]`       * # => [4, 9]*
+
+returns 2 elements starting at index 1. If there are no elements for the given indexes
+available, it returns *nil*:
+
+`  numbers[10, 2]`      * # => nil*
+
+Another way to select a subarray from an Array is to pass a *Range* of the wanted
+indexes to `[]`:
+
+`  numbers[1..2]`       * # => [4, 9]
+
+In case the elements are not available for the indexes it will again return *nil*:
+
+`  numbers[5..10]`      * # => nil*
+
+For further information about the `[]` method, see (ruby-doc core: Array#[]).
+
+---
+
+Create an Array of 5 different programming languages (as Strings) and store it in
+a *languages* variable.
+
+Define a variable *first* and assign the first programming language to it.
+
+Define a variable *last* and assign the last programming language to it.
+
+Store the middle 3 programming languages in a variable *some_languages*.
+
+---