Today I Learned

TIL, 2018-03-27. Redux Chapter at Last, Trying out Chef

Musings, Chef

  • Wah I was not even using my free tier account! :(
  • $ chef gem install knife-zero.
  • rails-server-template problem
  • Berkshelf: The dependency manager for Chef cookbooks.
  • Cookbooks are the modules that tell chef how to install a piece of software.
  • $ berks vendor ensures we have the correct cookbooks available in the folder berks-cookbooks. This path is specified in knife.rb.
  • Unable to authenticate (Chef): Add authorized_keys.
local_mode true
chef_repo_path   File.expand_path('../' , __FILE__)
cookbook_path ["cookbooks", "berks-cookbooks"]

knife[:ssh_attribute] = ""
knife[:use_sudo] = true
knife[:editor] = '/usr/local/bin/vim'
knife[:before_bootstrap] = "berks vendor"
knife[:before_converge]  = "berks vendor"

Musings, Ruby

  • High Voltage layout has to be below the include.
  • params[:action] to figure out what layout to render re: Bootstrap container lol.
  • Sticky footer solved by flexbox
  • Read up on gem configuration patterns-just put it in the lifelong-learning for now, when I need it.
  • The hidden costs of inheritance
    • Inheritance-based modeling is most commonly used for behavior sharing, but what it actually provides is implementation sharing. The greater the inheritance tree is, the chance of clashing with a variable used by an ancestor grows.
    • The lack of true private methods in Ruby complicates the system further: there isn’t a way to write a method in a parent object that a child object can’t clash with or override.
    • Gigantic interface (a million methods, lol).
    • Balancing reuse and customization?
  • AR tricks
    • Join with condition on the associated table: merge.
    • Subqueries: Post.where(user_id: User.created_last_month).
    • Booleans: Use User.where(tall: [false, nil]) because a .where.not will not catch the NULL case.
  • The Well-Grounded Rubyist, Chapter 6
    • Ruby initializes variables if it sees it, even if it won’t get executed. ` if false; x = 1; end #=> x is nil, not unknown`
    • Capture match in conditional: if m = /la/.match(name)
    • case operator: when matches on ===.
    • Blocks have access to the variables that already exist when they’re created, but block variables (those between the pipes) are not the same as the ones outside.
    • Semicolon in the parameter list: Doesn’t overwrite variables outside.
    • Exceptions that get raised are instances of a class, not the actual Exception class itself.
    • Pros of creating your own exception class:
      • Inherit from StandardError to have a meaningful exception name and refine the semantics of the rescue operation.
      • Self-documenting.
      • Able to rescue this specific exception.
  • The Well-Grounded Rubyist, Chapter 7
    • Literal constructors:, (you can’t do
    • inspect is for overriding, independently of whether you override to_s (which is used when it’s string interpolated). inspect is for other programmers.
    • A display method exists, it logs stuff out (default to STDOUT).
    • Star operator: Unwraps its operand into components.
    • Conversion vs typecasting: Calling methods like to_s, to_i, and to_f results in a new object, not like in C where you use the object as a string or an integer.
      • In a sense, all objects are typecasting themselves constantly.
    • Role-playing method
      • to_str
      • to_ary
    • Some cool shit:
      • Empty class definition = false
      • Non-empty class definition = the same value as the last value they contain
      • Method definitions are false, even if what they return is a true value

Musings, React

  • $ ./node_modules/.bin/babel-node app.js To execute JS, with babel-cli and babel-core in there? Lol.
  • Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: object. You likely forgot to export your component from the file it's defined in.
    • WTF, I just powered on this part.
  • Need to learn what export actually means. Reference
  • JS Spread syntax (…) Reference
    • Can be used for concatenating arrays, constructing objects/hashes.
  • To check if undefined in ES 2015+:
    • Just check varName === undefined or varName !== undefined.
  • this.forceUpdate() to force a re-render.
    • forceUpdate is discouraged.

``` js // Pass argument to event handlers Reference

onChange = (name, e) => { // ES6 way of dynamic keys Reference this.setState({ [name]:, }) };

<input onChange={(e) => this.onChange(‘name’, e)} value={} type=’text’ />

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