Ruby Koans checklist

generate_checklist.md

generate checklist

$ grep -r 'def test_' ruby_koans/src > koans_def.txt

ruby script to generate the checklist

def koans_def(path: 'koans_def.txt')
    koans = Hash.new{|hash, key| hash[key] = Array.new}
    File.readlines(path).map do |line|
        about, koan = line.split(/def test/)
        about.gsub!('ruby_koans/src/', '').gsub!(/.rb:.+/, '')
        koan.gsub!('_', ' ')
        koans[about] << koan
    end
    koans.select {|about, koans| /about_/.match about }
end

def generate_checklist()
    File.open('ruby_koans_checklist.txt', 'w') do |f|
        koans_def.each do |about, koans|
            f.puts
            f.puts '## ' + about
            koans.each do |koan|
                f.puts '- [ ]' + koan
            end
        end
    end
end

generate_checklist()

ruby_koans_checklist.md

ruby koans checklist

about_message_passing

• methods can be called directly
• methods can be invoked by sending the message
• methods can be invoked more dynamically
• send with underscores will also send messages
• classes can be asked if they know how to respond
• sending a message with arguments
• sending undefined messages to a typical object results in errors
• calling method missing causes the no method error
• all messages are caught
• catching messages makes respond to lie
• foo method are caught
• non foo messages are treated normally
• explicitly implementing respond to lets objects tell the truth

about_java_interop

• using a java library class
• java class can be referenced using both ruby and java like syntax
• include class includes class in module scope
• also java class can be given ruby aliases
• can directly call java methods on java objects
• jruby provides snake case versions of java methods
• jruby provides question mark versions of boolean methods
• java string are not ruby strings
• java strings can be compared to ruby strings maybe
• however most methods returning strings return ruby strings
• some ruby objects can be coerced to java
• some ruby objects are not coerced to what you might expect
• java collections are enumerable
• java class are open from ruby

about_dice_project

• can create a dice set
• rolling the dice returns a set of integers between 1 and 6
• dice values do not change unless explicitly rolled
• dice values should change between rolls
• you can roll different numbers of dice

about_strings

• double quoted strings are strings
• single quoted strings are also strings
• use single quotes to create string with double quotes
• use double quotes to create strings with single quotes
• use backslash for those hard cases
• use flexible quoting to handle really hard cases
• flexible quotes can handle multiple lines
• here documents can also handle multiple lines
• plus will concatenate two strings
• plus concatenation will leave the original strings unmodified
• plus equals will concatenate to the end of a string
• plus equals also will leave the original string unmodified
• the shovel operator will also append content to a string
• the shovel operator modifies the original string
• double quoted string interpret escape characters
• single quoted string do not interpret escape characters
• single quotes sometimes interpret escape characters
• double quoted strings interpolate variables
• single quoted strings do not interpolate
• any ruby expression may be interpolated
• you can get a substring from a string
• you can get a single character from a string
• in older ruby single characters are represented by integers
• in modern ruby single characters are represented by strings
• strings can be split
• strings can be split with different patterns
• strings can be joined
• strings are unique objects

about_classes

• instances of classes can be created with new
• instance variables can be set by assigning to them
• instance variables cannot be accessed outside the class
• you can politely ask for instance variable values
• you can rip the value out using instance eval
• you can create accessor methods to return instance variables
• attr reader will automatically define an accessor
• attr accessor will automatically define both read and write accessors
• initialize provides initial values for instance variables
• args to new must match initialize
• different objects have different instance variables
• inside a method self refers to the containing object
• to s provides a string version of the object
• to s is used in string interpolation
• inspect provides a more complete string version
• all objects support to s and inspect

about_modules

• cant instantiate modules
• normal methods are available in the object
• module methods are also available in the object
• module methods can affect instance variables in the object
• classes can override module methods

about_array_assignment

• non parallel assignment
• parallel assignments
• parallel assignments with extra values
• parallel assignments with splat operator
• parallel assignments with too few variables
• parallel assignments with subarrays
• parallel assignment with one variable
• swapping with parallel assignment

about_open_classes

• as defined dogs do bark
• after reopening dogs can both wag and bark
• even existing built in classes can be reopened

about_to_str

• to s returns a string representation
• normally objects cannot be used where strings are expected
• to str also returns a string representation
• to str allows objects to be treated as strings
• user defined code can check for to str

about_symbols

• symbols are symbols
• symbols can be compared
• identical symbols are a single internal object
• method names become symbols
• constants become symbols
• symbols can be made from strings
• symbols with spaces can be built
• symbols with interpolation can be built
• to s is called on interpolated symbols
• symbols are not strings
• symbols do not have string methods
• symbols cannot be concatenated
• symbols can be dynamically created

about_iteration

• each is a method on arrays
• iterating with each
• each can use curly brace blocks too
• break works with each style iterations
• collect transforms elements of an array
• select selects certain items from an array
• find locates the first element matching a criteria
• inject will blow your mind
• all iteration methods work on any collection not just arrays

about_methods

• calling global methods
• calling global methods without parentheses
• sometimes missing parentheses are ambiguous
• calling global methods with wrong number of arguments
• calling with default values
• calling with variable arguments
• method with explicit return
• method without explicit return
• calling methods in same class
• calling methods in same class with explicit receiver
• calling private methods without receiver
• calling private methods with an explicit receiver
• calling methods in other objects require explicit receiver
• calling private methods in other objects

about_keyword_arguments

• keyword arguments
• keyword arguments with wrong number of arguments

about_nil

• nil is an object
• you dont get null pointer errors when calling methods on nil
• nil has a few methods defined on it

about_objects

• everything is an object
• objects can be converted to strings
• objects can be inspected
• every object has an id
• every object has different id
• small integers have fixed ids
• clone creates a different object

about_constants

• nested constants may also be referenced with relative paths
• top level constants are referenced by double colons
• nested constants are referenced by their complete path
• nested classes inherit constants from enclosing classes
• subclasses inherit constants from parent classes
• who wins with both nested and inherited constants
• who wins with explicit scoping on class definition

about_exceptions

• exceptions inherit from Exception
• rescue clause
• raising a particular error
• ensure clause
• asserting an error is raised #

about_scope

• dog is not available in the current scope
• you can reference nested classes using the scope operator
• bare bones class names assume the current scope
• nested string is not the same as the system string
• use the prefix scope operator to force the global scope
• constants are defined with an initial uppercase letter
• class names are just constants
• constants can be looked up explicitly
• you can get a list of constants for any class or module

about_proxy_object_project

• proxy method returns wrapped object
• tv methods still perform their function
• proxy records messages sent to tv
• proxy handles invalid messages
• proxy reports methods have been called
• proxy counts method calls
• proxy can record more than just tv objects
• it turns on
• it also turns off
• edge case on off
• can set the channel

about_triangle_project_2

• illegal triangles throw exceptions

about_control_statements

• if then else statements
• if then statements
• if statements return values
• if statements with no else with false condition return value
• condition operators
• if statement modifiers
• unless statement
• unless statement evaluate true
• unless statement modifier
• while statement
• break statement
• break statement returns values
• next statement
• for statement
• times statement

about_arrays

• creating arrays
• array literals
• accessing array elements
• slicing arrays
• arrays and ranges
• slicing with ranges
• pushing and popping arrays
• shifting arrays

about_hashes

• creating hashes
• hash literals
• accessing hashes
• accessing hashes with fetch
• changing hashes
• hash is unordered
• hash keys
• hash values
• combining hashes
• default value
• default value is the same object
• default value with block

about_scoring_project

• score of an empty list is zero
• score of a single roll of 5 is 50
• score of a single roll of 1 is 100
• score of multiple 1s and 5s is the sum of individual scores
• score of single 2s 3s 4s and 6s are zero
• score of a triple 1 is 1000
• score of other triples is 100x
• score of mixed is sum

about_true_and_false

• true is treated as true
• false is treated as false
• nil is treated as false too
• everything else is treated as true

about_triangle_project

• equilateral triangles have equal sides
• isosceles triangles have exactly two sides equal
• scalene triangles have no equal sides

about_class_methods

• objects are objects
• classes are classes
• classes are objects too
• objects have methods
• classes have methods
• you can define methods on individual objects
• other objects are not affected by these singleton methods
• since classes are objects you can define singleton methods on them too
• class methods are independent of instance methods
• classes and instances do not share instance variables
• you can define class methods inside the class
• class statements return the value of their last expression
• self while inside class is class object not instance
• you can use self instead of an explicit reference to dog
• heres still another way to write class methods
• heres an easy way to call class methods from instance methods

about_inheritance

• subclasses have the parent as an ancestor
• all classes ultimately inherit from object
• subclasses inherit behavior from parent class
• subclasses add new behavior
• subclasses can modify existing behavior
• subclasses can invoke parent behavior via super
• super does not work cross method

about_sandwich_code

• counting lines
• finding lines
• counting lines2
• finding lines2
• open handles the file sandwich when given a block

about_regular_expressions

• a pattern is a regular expression
• a regexp can search a string for matching content
• a failed match returns nil
• question mark means optional
• plus means one or more
• asterisk means zero or more
• the left most match wins
• character classes give options for a character
• slash d is a shortcut for a digit character class
• character classes can include ranges
• slash s is a shortcut for a whitespace character class
• slash w is a shortcut for a word character class
• period is a shortcut for any non newline character
• a character class can be negated
• shortcut character classes are negated with capitals
• slash a anchors to the start of the string
• slash z anchors to the end of the string
• caret anchors to the start of lines
• dollar sign anchors to the end of lines
• slash b anchors to a word boundary
• parentheses group contents
• parentheses also capture matched content by number
• variables can also be used to access captures
• a vertical pipe means or
• scan is like find all
• sub is like find and replace
• gsub is like find and replace all

about_blocks

• methods can take blocks
• blocks can be defined with do end too
• blocks can take arguments
• methods can call yield many times
• methods can see if they have been called with a block
• block can affect variables in the code where they are created
• blocks can be assigned to variables and called explicitly
• stand alone blocks can be passed to methods expecting blocks
• methods can take an explicit block argument

about_asserts

• assert truth
• assert with message
• assert equality
• a better way of asserting equality
• fill in values