ruby notes

Home

Check out aiproxy.pro

Ruby equivalent of optional chaining

The equivalent of the swift statement:

service_endpoints.endpointable?.path ?? ""

service_endpoints.endpointable&.path || ""

Ruby gotcha, there is no `first(where:)`

Switching back and forth from swift, I wrote this in ruby (simplified):

[1,2,3].first { |x| x == 1 } # => 1

It appears to work as intended, but that’s only for this special case. Observe:

[1,2,3].first { |x| x == 2 } # => 1

Not what I want! The correct equivalent of first(where:) is find:

[1,2,3].find { |x| x == 2 } # => 2

Ruby assign results of last repl command to variable

1 + 1  
x = _  
x # => 2

Ruby save file from repl

Equivalent of ipython’s %save:

./bin/rails c  
> Pry.start  
> # prototype  
> hist --save myfile.rb

Ruby static method style

I prefer

class << self  
  def my_method  
  end  
end

Over

def self.my_method  
end

Becuase it makes it easier to ack/grep for definition of my_method without guessing the style

Ruby case statement

x = 'a'  
y = case x  
    when 'a'  
      1  
    when 'b'  
      2  
    else  
      3  
    end

x = 'a'  
y = case x  
    when 'a' then 1  
    when 'b' then 2  
    else 3  
    end

Ruby threads

Get current number of threads with Thread.list.

Threads are torn down when they run to completion. E.g.

Thread.list #=> [main]  
Thread.new { puts "hello world"; sleep(1) }  
Thread.list #=> [main, new-thread]  
:: wait one second  
Thread.list #=> [main]

Threads can be killed:

t = Thread.new { sleep(1000) }  
t.kill

Ruby get the source location of a method

A couple ways to find where a ruby method or class is defined:

Use instance_method in the repl. For example:

irb
require ‘mail’
Mail::Sendmail.instance_method(:deliver!) # =>
# => #<UnboundMethod: Mail::Sendmail#deliver!(mail) /Users/lzell/.rvm/gems/ruby-3.2.2/gems/mail-2.8.1/lib/mail/network/delivery_methods/sendmail.rb:64>
Use the source_location helper:

Redis.new.method(:publish).source_location

Ruby gotcha

Time#utc mutates self:

now = Time.now  
now.utc  
now

Ruby gotcha

Closures behave differently depending on if they are defined using proc or lambda

def a  
  x = proc { return }  
  x.call()  
  puts "You never see me"  
end  

a() // Doesn't print anything  

def b  
  x = lambda { return }  
  x.call()  
  puts "But you do see me"  
end  

b() // Prints "But you do see me"  

def c  
  x = -> { return }  
  x.call()  
  puts "And you see me too"  
end  

c() // Prints "And you see me too"

How to map from a range

Subtle syntax difference results in major functional change:

[0..10].map { 1 }  
# => [1]  

(0..10).map { 1 }  
[1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1]

Replace characters with tr

"1337".tr("137", "let")  
# => "leet"

Reminder that if/else are expressions in ruby:

a = if true  
  "hello"  
else  
  "world"  
end

(ruby, install, 3.2.2, rvm, openssl)

I was having problems installing ruby on a friend’s machine.
Had to use:

rvm install ruby-3.2.2 --with-openssl-dir=$(brew --prefix openssl)

(ruby repl, irb, insert line in existing function)

Up arrow to previously executed code in irb
Use Opt+Enter to add a new line without executing

(ruby, system, exception, raise if error from shell, default does not raise)

None of these raise by default:

system "exit 1"  
`exit 1`  
%x(exit 1)

Instead, use:

system "exit 1", exception: true

(ruby, map, symbol syntax, symbol to proc)

The symbol to proc functionality assumes that the symbol is a member of the
calling instance. To call a pure function, use my_array.map(&method(:my_fn)).
For example:

def add_one(n)  
  return n + 1  
end  

[1,2,3].map &method(:add_one)

(ruby debug, ruby 3)

Either use:

require "debug"  
:: Add breakpoint in source with `debugger`

Or add binding.irb in source, no require necessary.
I prefer the former, because stepping (n) and continuing (c) through the source works.

Move down: Tab
Move up: Shift-Tab

(ruby disable irb autocomplete)

Start irb with irb --noautocomplete
or add IRB.conf[:USE_AUTOCOMPLETE] = false to ~/.irbrc

(ruby, erb, howto)

In the template, myfile.txt.erb, use placeholders like <%= my_variable %>
In the doc generator, generator.rb:

    require "erb"  
    my_variable = "hello world"  
    result = ERB.new(File.read("myfile.txt.erb")).result(binding)  
    File.write("myfile.txt", result)

Call the generator with ruby generator.rb, and observe myfile.txt on disk.

(rvm upgrade, rvm update ruby version)

rvm get stable

(rvm set default ruby version)

rvm --default use X.Y.Z

(rvm, ruby, remove rvm)

rvm implode

(rvm, name a version of ruby for local use)

rvm alias create myruby ruby-2.4.1  
rvm use myruby

(ruby, global vars, cheat sheet)

https://gist.github.com/dvliman/10402435

(ruby gem install dir)

See where bundler finds a specific gem:

bundle show <gemname>

(ruby koans, assert, testing, education)

https://www.rubykoans.com/

(ruby ruby, sexp, lexer, parser, tokenize)

http://ruby-doc.org/stdlib-2.2.0/libdoc/ripper/rdoc/Ripper.html

(ruby, find methods defined lower in class tree)

List methods on an instance that are defined outside of Object:

class Object  
    def local_methods  
      (methods - Object.instance_methods).sort  
    end  
end

Can also try:

 ActiveSupport::MessageEncryptor.methods - Object.methods

(ruby, irb, faulty ~/.irbrc, debugging)

To see why ~/.irbrc is not working properly:

ruby ~/.irbrc

(irb, default configuration)

/private/etc/irbrc holds the default irb config, can be overwritten by creating a ~/.irbrc file.

(ruby, rackup, reload on file system changes)

See the rerun gem

$ rerun --background --no-growl rackup service.ru

(ruby, pry, irb, autocomplete, source exploration, discovery)

Pry is really sweet.

$ pry  
> cd FileUtils  
> ls  
> show-method mkdir

(ruby, time, active support, time helpers, number of seconds)

require 'active_support/time'

I added this here:
https://stackoverflow.com/a/14725405/143447

(irb, source exploration, discovery)

Given a starting value, see what method will give the desired result with what_methods.
E.g.

require 'what_methods'  
10.what? "10" #=> 10.to_s, 10.inspect

2012

(ruby, colorize irb prompt, colorize rails console prompt):

require "wirble"  
IRB.CurrentContext.prompt_i = Wirble::Colorize.colorize_string(IRB.CurrentContext.prompt_i, :red)

(ruby, gems, get location on disk)

gem env

(rvm, which rvm)

After installing rvm, I was surprised that which rvm exited with 1.
rvm is a function that’s sourced into my shell.
Use command -v rvm to see if my shell can find it.
Use bash --debugger -cl "declare -F rvm" to find where the function is defined.
The output will contain the definition file on disk and the source line number.

(ruby, rubygems, load automatically)

Do not add require "rubygems" to code.
Start ruby with ruby -rubygems, or irb with irb -rrubygems, or add this to ~/.bash_profile:

export RUBYOPT="rubygems"

source: https://tomayko.com/blog/2009/require-rubygems-antipattern

(ruby, regex, dot star, does not match new line)

Here is an interesting difference:

irb> a = "string with \n new line"  
irb> a =~ /(.*)/  
irb> $1  
=> "string with "  

irb> a =~ /([^"]*)/  
irb> $1  
=> "string with \n new line"

The .* does not match new lines, but negated class does

(ruby, class variables, inheritance works as expected)

class A  
  @greeting = "hello"  
  class << self  
    attr_reader :greeting  
  end  
end  

class B < A  
  @greeting = "hola"  
end  

A.greeting # => "hello"  
B.greeting # => "hola"

(ruby, iterate all error classes at runtime)

ObjectSpace.each_object(Class) do |cls|  
  if cls.ancestors.include? Exception  
    puts cls  
  end  
end

(ruby, irb, find class name in irb)

irb> self.class.constants.select { |c| c =~ /needle/i }

(ruby, send message, dynamic, dynamic method call)

object.message is the same as object.send(:message)

For example, 5.send :to_s

(ruby, variable in regex)

a = "[0-9]+"  
b = /#{a}/

(ruby, pad a month string to two digits)

month = 5  
month.to_s.gsub(/^(\d)$/, '0\1')

(ruby, add N months to current month)

month = ((month - 1 + N ) % 12) + 1

(ruby, irb, benchmark in irb)

require 'benchmark'  
include Benchmark  

bm(10) do |test|  
    test.report("result 1:") do  
      # test something  
    end  
    test.report("result 2:") do  
      # test something else  
    end  
end

(ruby, reference semantics, array, create array of empty arrays)

Gotcha:

array = Array.new(2,[])  
array[0][0] = "x"  
array  
# => [["x"], ["x"]]  
# Both subarrays are filled with "x" (it's really one array)

Use:

array = Array.new(2) { [] }  
array[0][0] = "x"  
array  
# => [["x"], []]

(ruby, instance eval, I thought this was once a good idea)

These accomplish the same thing:

class Test  
  attr_accessor :one, :two, :three  
  def initialize(one, two, three)  
    @one = one  
    @two = two  
    @three = three  
  end  
end  
Test.new(1,2,3)

and

class Test  
    attr_accessor :one, :two, :three  
    def initialize(&block)  
        instance_eval &block  
    end  
end  
Test.new {self.one = 1; self.two = 2; self.three = 3}

(ruby, color, term, escape code, irb)

Loop through escape sequences in IRB to pick a color:

(30..50).each do |x|  
  puts x  
  print "\e[#{x}mTEST\e[0m\n"  
end

(ruby, is daylight savings in effect?)

Time.now.isdst

Ruby equivalent of optional chaining

Ruby gotcha, there is no first(where:)

Ruby assign results of last repl command to variable

Ruby save file from repl

Ruby static method style

Ruby case statement

Ruby threads

Ruby get the source location of a method

Ruby gotcha

Ruby gotcha

How to map from a range

Replace characters with tr

Reminder that if/else are expressions in ruby:

(ruby, install, 3.2.2, rvm, openssl)

(ruby repl, irb, insert line in existing function)

(ruby, system, exception, raise if error from shell, default does not raise)

(ruby, map, symbol syntax, symbol to proc)

(ruby debug, ruby 3)

(ruby 3 irb autocomplete, navigate autocomplete popup)

(ruby disable irb autocomplete)

(ruby, erb, howto)

(rvm upgrade, rvm update ruby version)

(rvm set default ruby version)

(rvm, ruby, remove rvm)

(rvm, name a version of ruby for local use)

(ruby, global vars, cheat sheet)

(ruby gem install dir)

(ruby koans, assert, testing, education)

(ruby ruby, sexp, lexer, parser, tokenize)

(ruby, find methods defined lower in class tree)

(ruby, irb, faulty ~/.irbrc, debugging)

(irb, default configuration)

(ruby, rackup, reload on file system changes)

(ruby, pry, irb, autocomplete, source exploration, discovery)

(ruby, time, active support, time helpers, number of seconds)

(irb, source exploration, discovery)

2012

(ruby, colorize irb prompt, colorize rails console prompt):

(ruby, gems, get location on disk)

(rvm, which rvm)

(ruby, rubygems, load automatically)

(ruby, regex, dot star, does not match new line)

(ruby, class variables, inheritance works as expected)

(ruby, iterate all error classes at runtime)

(ruby, irb, find class name in irb)

(ruby, send message, dynamic, dynamic method call)

(ruby, variable in regex)

(ruby, pad a month string to two digits)

(ruby, add N months to current month)

(ruby, irb, benchmark in irb)

(ruby, reference semantics, array, create array of empty arrays)

(ruby, instance eval, I thought this was once a good idea)

(ruby, color, term, escape code, irb)

(ruby, is daylight savings in effect?)

Ruby gotcha, there is no `first(where:)`