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## 代码规范
1. 使用UTF-8编码
2. 使用空格缩进，不使用tab, 1 tab = 2 spaces
3. 不需要使用分号(;)和反斜杠(\)连接代码
Demo
```ruby
# basic types
a = 1
b = "hello world"
# one line
c = ["pear", "cat", "dog"]
# or multiple lines
c2 = [
"pear",
"cat",
"dog"
]
d = { name:"world", age:18 }
d2 = {
name:"world",
age:18
}
# source layout, conversion
# with or without()
def hello(name, age = 18)
puts "hello #{name}, and age is #{age}"
end
def hello name, age = 18
puts "hello #{name}, and age is #{age}"
end
```
## 变量类型
1. local variables 局部变量: a = 1,b = "hello
2. constants 常量: Names = ['john','alex']
3. global variables 全局变量: $platform = 'mac'
4. instance variables 实例变量: @name = 'world'
5. class variables 类变量: @@counter = 20
```ruby
# variables scope
# constant
Name = 'world'
Name = 'worlds' # => output wraning
Name.replace 'world_2' # => safe
puts Name
```
```ruby
# instance variable and class variable
class User
# 相当于定义一个get操作：相当于有一个name的实例变量
# 使用attr_reader关键字，实现把内部的实例变量 向外部保留一个访问接口
attr_reader :name
## 相当于静态变量
@@counter = 0
def initialize name
@name = name
@@counter += 1 #记录实例化次数
end
def get_counter
@@counter
end
end
user = User.new 'world'
puts user.name
puts user.get_counter
```
```ruby
# variables scope
# global variables
def hello
puts $$ #=> process id
p $: # => ruby loading path
end
hello
```
## Boolean表达式
1. %%, ||, !
2. And, Or, Not
```ruby
#boolean clause
puts (true and true)
puts (true and false)
puts (true or false)
puts (not true)
```
```ruby
#boolean clause
a = (false and false || true) # 先|| 再and
b = (false and false or true) # 优先级相同 先 and 再or
puts a
puts b
```
```ruby
#boolean clause
a = nil
b = a || 4 # 如果a是成立的(不是false和nim) 那么a赋值给b 否则赋值4给b
puts b # => 4
c = b && 5 # 如果b成立那么执行 c = 5
puts c # => 5
```
```ruby
#boolean clause
# preference
# and or not 优先级 低于 && || ! =
a = nil
b = a or 4 # or 优先级 低于 = 操作符 所以实际吧a赋值给b 然后 or 4
puts b # => will be nil
c = b && 5 # b是nil 所有 b&&5 不成立 所以 c =nil
puts c #=> will be nil
```
## String,Hash和Array常用方法
```ruby
# string
a = "hello world"
a.empty? # => false
a[0] = "a" # => aello world
a.freeze
a[0] = "h" # => will raise error
a = "hello" # =>ok, re-assign value
```
```ruby
# string
a = "hello world"
a.reverse # => dlrow olleh
# both of these method have ! version
a.sub('o', 'A') # =>hellA world
a.gsub('o', 'A') # => hellA wArld
a.start_with? 'h' # => true
a.end_with? 'd' # => true
a.include? 'o'
```
```ruby
# string
a = "hello world"
b = a.split(' ') # => ["hello", "world"]
b.join(' ') # => hello world
```
```ruby
# string
# variable refer
a = "hello world"
b = a # 将字符串的引用地址 或者说指针 给了b
puts b
b[0] = "A"
puts a # => Aello world
puts '-' * 30
a = "hello world"
b = a.dup # what's the difference with String#clone method? 完整复制， 不是引用了
b[0] = "A"
puts b # => Aello world
puts a # => hello world
#output
hello world
Aello world
------------------------------
Aello world
hello world
```
```ruby
# array
a = ["pear", "cat", "horse"]
puts a.join(' ') # 数组中必须都是字符串 才可以用字符连接
a.clear #清空数组
a.find {|x| x == 'horse'} #查找匹配到的
a.map {|x| x.upcase} # 迭代执行
a.collect {|x| x.upcase} #map方法的别名
a.uniq #排除多余重复
a.flatten #吧二维或者多维转换以为
a.sort #排序
a.count #元素数量
a.delete_if {|x| x == 'horse'} #匹配则删除
a.each {|x| puts x} #遍历
```
```ruby
# hash
a = {name: 'world', age: 18}
a.each {|key, value| puts key} #遍历
a.keys # 所有key
a.values # 所有value
a.has_key? :name #判断是否有key
a.delete :name #删除key
a.delete_if #匹配则删除
```
## 其他
Buildin Methods
1. send:private method and method as a variable #调用私有方法，调用的方法名是个遍历的时候 使用send(元编程)
2. respond_to? #探测实例是否有给定方法
3. demo
```ruby
# send method
def hello
puts 'hello world'
end
send(:hello)
```
```ruby
# respond_to?
a = "hello world"
puts a.respond_to?(:length)
```
## 代码加载机制
### $LOAD_PATH
ruby中的特殊变量 在irb中可以直接输出，当加载模块的时候ruby会在的各个目录中查找加载,如果查找不到会抛出异常
### 命名约束
ruby中每一个文件都是一个独立的文件。文件名和文件中的类名(模块名)对应
```ruby
file_name: user_session.rb
class_name: UserSession
```
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