3014zhangshuo

class Hash
  # Returns a new hash with +self+ and +other_hash+ merged recursively.
  #
  #   h1 = {:x => {:y => [4,5,6]}, :z => [7,8,9]}
  #   h2 = {:x => {:y => [7,8,9]}, :z => "xyz"}
  #
  #   h1.deep_merge(h2) #=> { :x => {:y => [7, 8, 9]}, :z => "xyz" }
  #   h2.deep_merge(h1) #=> { :x => {:y => [4, 5, 6]}, :z => [7, 8, 9] }
  def deep_merge(other_hash)
    dup.deep_merge!(other_hash)

3014zhangshuo

bundle exec rake db:drop RAILS_ENV=test
bundle exec rake db:create RAILS_ENV=test
bundle exec rake db:schema:load RAILS_ENV=test

3014zhangshuo

a = Article.find(3)
a[param] = "value"
a.save

# or

a = Article.find(3)
a.send("#{param}=", "value")
a.save

3014zhangshuo

https://zh.wikipedia.org/wiki/%E9%80%89%E6%8B%A9%E6%8E%92%E5%BA%

选择排序的交换操作介于 {\displaystyle 0} {\displaystyle 0}和 {\displaystyle (n-1)} (n-1)次之间。选择排序的比较操作为 {\displaystyle n(n-1)/2} n(n-1)/2次。选择排序的赋值操作介于 {\displaystyle 0} {\displaystyle 0}和 {\displaystyle 3(n-1)} 3(n-1)次之间。

比较次数 {\displaystyle O(n^{2})} O(n^{2})，比较次数与关键字的初始状态无关，总的比较次数 {\displaystyle N=(n-1)+(n-2)+...+1=n\times (n-1)/2} N=(n-1)+(n-2)+...+1=n\times (n-1)/2。交换次数 {\displaystyle O(n)} O(n)，最好情况是，已经有序，交换0次；最坏情况是，逆序，交换 {\displaystyle n-1} n-1次。交换次数比冒泡排序较少，由于交换所需CPU时间比比较所需的CPU时间多， {\displaystyle n} n值较小时，选择排序比冒泡排序快。

原地操作几乎是选择排序的唯一优点，当空间复杂度要求较高时，可以考虑选择排序；实际适用的场合非常罕见。

3014zhangshuo

class ApplicationController < ActionController::Base
  rescue_from ActiveRecord::RecordNotFound, with: :record_not_found
  
  private
  def record_not_found
    render plain "404 not found", status: 404
  end
end

3014zhangshuo

apt update && apt upgrade

apt install ruby vim git nodejs

apt install ruby-dev libxml2-dev libxslt-dev pkg-config make clang
gem install nokogiri -- --use-system-libraries

apt install libsqlite-dev
gem install sqlite3

3014zhangshuo

class DummyController < ApplicationController
  def do
    render json: { balance: 50 }
  end
end

3014zhangshuo

module A
  def self.included(target)
    v = target.instance_methods.include?(:method_name)
    puts "in included: #{v}"
  end

  def self.append_features(target)
    v = target.instance_methods.include?(:method_name)
    puts "in append features before: #{v}"
    super

3014zhangshuo

class @CubicEquations #加入 @ 跨作用域 绑定外层 this
  constructor: (@a, @b, @c, @d) ->
    @init()
    @calc()
    @result()

  get_cube_root = (value) ->
    if value < 0
      -Math.pow(-value, 1/3)
    else if value > 0

3014zhangshuo

# source: https://apidock.com/ruby/Hash/delete
class Hash
  def without(*keys)
    cpy = self.dup
    keys.each { |key| cpy.delete(key) }
    cpy
  end
end

h = { :a => 1, :b => 2, :c => 3 }