Idiosyncratic Ruby
Quiz
idiosyncratic-ruby.com
Documenting lesser-known features in Ruby
2021: "Stay at home to learn Ruby 3.0"
Ruby's Magic Comments
Also known as:
interpreter instructions or compiler directives
Setting a source file's encoding:
# encOding: bInary
p "".encoding # => #<Encoding:ASCII-8BIT>Magic Comments
How many different "magic" comments (a.k.a interpreter instructions) do exist in Ruby 3.0?
1
2
3
4
5
6
Magic Comments
How many different "magic" comments (a.k.a interpreter instructions) do exist in Ruby 3.0?
4
# encoding: …
# frozen_string_literal: …
# warn_indent: …
# shareable_constant_value: … ← NEW
# warn_past_scope: … ← NOT COUNTED
Magic Comments
What happens when you specify# shareable_constant_value: literal
as your magic comment?
It deep-freezes every literal assigned to a constant
or
It deactivates the warning when you are re-assigning a constant
or
It calls Object#share on every literal assigned to a constant
or
It literally allows you to share the constant's source code on github.com
Magic Comments
What happens when you specify# shareable_constant_value: literal
as your magic comment?
It deep-freezes every literal assigned to a constant
X = [{foo: []}]
# => same as [{foo: [].freeze}.freeze].freeze
Other modes of operation:
experimental_everything-
experimental_copy
Magic Comments
Where can you place your# shareable_constant_value
magic comment?
Only in the first line of the file
or
In the first line of the file, but when its taken by a Unix shebang (#!/bin/ruby), or another magic comment, it is possible to put in a subsequent line
or
Anywhere in the file
Magic Comments
Where can you place your# shareable_constant_value
magic comment?
Anywhere in the file
Changes the behavior of constants below the magic comment within the current module-scope
Magic Comments - Resources
Grammar Definition:
github.com/ruby/ruby/blob/v3_0_0/parse.y#L8085
Official Documentation:
ruby-doc.org/core-3.0.0/doc/syntax/comments_rdoc.html
More Examples:
idiosyncratic-ruby.com/58-magic-instructions.html
Random 3.0 News
Random 3.0 News
What does ... (three dots) do in Ruby 3.0?
Calls a method without any arguments three times or
Forwards a method's arguments to another method or
It is a begin- and endless range (-Infinity to Infinity) or
Separates the RBS type signature from the actual method body
Random 3.0 News
What does ... (three dots) do in Ruby 3.0?
Forwards a method's arguments
to another method
Originally introduced in 2.7,
it has become useful in 3.0:
def repeat(method_to_call, count, ...)
puts "Will call #{method_to_call} #{count} times"
count.times {
public_send(method_to_call, ...)
}
endRandom 3.0 News
How many of Ruby's 90 default gems are officially unmaintained?
None (all have a maintainer)
1-5
6-10
11-20
21-30
Random 3.0 News
How many of Ruby's 90 default gems are officially unmaintained?
17
benchmark date dbm debug delegate english fileutils getoptlong net-pop net-protocol net-smtp observer open3 pstore tempfile tmpdir weakref
Random 3.0 News
Which global variable was removed from Ruby 3.0?
$-0
$-F
$-I
$-K
Random 3.0 News
Which global variable was removed from Ruby 3.0?
$-K
Removed together with $KCODE
Used to change the behavior of default encodings
Mirrored the -K CLI option (which is still present)
Random 3.0 News
Which one of the following statements is not valid Ruby 3.0?
def * = 0
def Time.now = 1970
def !(o) = !!(o)
def a x = x ** 2
Random 3.0 News
Which one of the following statements is not valid Ruby 3.0?
def a x = x ** 2
Endless method definitions with arguments require parenthesis:
def a(x) = x ** 2
Random 3.0 News
What is the output of the following Ruby 3.0 code:
a = 1
2 => a
def a = 3
p a
1
2
3
Random 3.0 News
What is the output of the following Ruby 3.0 code:
a = 1
2 => a
def a = 3
p a
2
Local variable a has precedence over method a
Ruby 3.0 Resources
Things I did not cover:
Keyword argument changes, typing with rbs and typeprof, Ractor for concurrency, ...
Checkout Ruby Changes 3.0
at the Ruby Reference by @zverok
Single-line Pattern Matching /
Right Hand Assignment
Warning[:experimental] = false
# Check if a is true and b is false
if [a, b] in [true, false]
# Separate an array into head an tail
array => [first, *rest]Single-line Pattern Matching
Which one of the following statements returns false?
2 in 1...3
2 in [1,2,3]
BasicObject in Object
Object in BasicObject
Single-line Pattern Matching
Which one of the following statements returns false?
2 in [1,2,3] # => false
2 => [1,2,3] # NoMatchingPatternError (2)
Single-line Pattern Matching
Which one of the following one-liners does not work?
1 => Numeric => x
2 => a => b => c => d
3 => Integer => Z
4 => -> o { p o } => o
Single-line Pattern Matching
Which one of the following one-liners does not work?
3 => Integer => Z
syntax error, unexpected constant,
expecting local variable or method
Single-line Pattern Matching
Which one of the following statements will raise an error?
0 => 0
0 => 0 => o
0 => 0.0 => o
0 => 0...0 => o
Single-line Pattern Matching
Which one of the following statements will raise an error?
0 => 0...0 => o
# NoMatchingPatternError (0)
0 => 0..0 => o
# => 0
Single-line Pattern Matching
Which of the following new syntaxes is just super neat and awesome?
{ key: 'value' } in { key: }
Returns true if all specified keys were found
Object destructuring: It assigns the specified keys' values to local variables with the keys' names
Ruby got better!
So let's make 2021 better, too ;)
@JanLelis - idiosyncratic-ruby.com/quiz