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568 lines
11 KiB
Markdown
568 lines
11 KiB
Markdown
---
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language: crystal
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filename: learncrystal-cn.cr
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contributors:
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- ["Vitalii Elenhaupt", "http://veelenga.com"]
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- ["Arnaud Fernandés", "https://github.com/TechMagister/"]
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translators:
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- ["Xuty", "https://github.com/xtyxtyx"]
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lang: zh-cn
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---
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```crystal
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# 这是一行注释
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# 一切都是对象(object)
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nil.class #=> Nil
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100.class #=> Int32
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true.class #=> Bool
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# nil, false 以及空指针是假值(falsey values)
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!nil #=> true : Bool
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!false #=> true : Bool
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!0 #=> false : Bool
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# 整数类型
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1.class #=> Int32
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# 四种有符号整数
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1_i8.class #=> Int8
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1_i16.class #=> Int16
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1_i32.class #=> Int32
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1_i64.class #=> Int64
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# 四种无符号整数
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1_u8.class #=> UInt8
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1_u16.class #=> UInt16
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1_u32.class #=> UInt32
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1_u64.class #=> UInt64
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2147483648.class #=> Int64
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9223372036854775808.class #=> UInt64
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# 二进制数
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0b1101 #=> 13 : Int32
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# 八进制数
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0o123 #=> 83 : Int32
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# 十六进制数
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0xFE012D #=> 16646445 : Int32
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0xfe012d #=> 16646445 : Int32
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# 浮点数类型
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1.0.class #=> Float64
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# Crystal中有两种浮点数
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1.0_f32.class #=> Float32
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1_f32.class #=> Float32
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1e10.class #=> Float64
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1.5e10.class #=> Float64
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1.5e-7.class #=> Float64
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# 字符类型
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'a'.class #=> Char
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# 八进制字符
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'\101' #=> 'A' : Char
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# Unicode字符
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'\u0041' #=> 'A' : Char
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# 字符串
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"s".class #=> String
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# 字符串不可变(immutable)
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s = "hello, " #=> "hello, " : String
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s.object_id #=> 134667712 : UInt64
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s += "Crystal" #=> "hello, Crystal" : String
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s.object_id #=> 142528472 : UInt64
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# 支持字符串插值(interpolation)
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"sum = #{1 + 2}" #=> "sum = 3" : String
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# 多行字符串
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"这是一个
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多行字符串"
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# 书写带有引号的字符串
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%(hello "world") #=> "hello \"world\""
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# 符号类型
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# 符号是不可变的常量，本质上是Int32类型
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# 符号通常被用来代替字符串，来高效地传递特定的值
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:symbol.class #=> Symbol
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sentence = :question? # :"question?" : Symbol
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sentence == :question? #=> true : Bool
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sentence == :exclamation! #=> false : Bool
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sentence == "question?" #=> false : Bool
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# 数组类型(Array)
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[1, 2, 3].class #=> Array(Int32)
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[1, "hello", 'x'].class #=> Array(Int32 | String | Char)
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# 必须为空数组指定类型
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[] # Syntax error: for empty arrays use '[] of ElementType'
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[] of Int32 #=> [] : Array(Int32)
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Array(Int32).new #=> [] : Array(Int32)
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# 数组可以通过下标访问
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array = [1, 2, 3, 4, 5] #=> [1, 2, 3, 4, 5] : Array(Int32)
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array[0] #=> 1 : Int32
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array[10] # raises IndexError
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array[-6] # raises IndexError
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array[10]? #=> nil : (Int32 | Nil)
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array[-6]? #=> nil : (Int32 | Nil)
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# 使用负位置编号，从后往前访问数组
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array[-1] #=> 5
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# With a start index and size
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# 使用起始位置编号+大小
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array[2, 3] #=> [3, 4, 5]
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# 使用范围(range)访问数组
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array[1..3] #=> [2, 3, 4]
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# 向尾部添加元素
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array << 6 #=> [1, 2, 3, 4, 5, 6]
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# 删除尾部元素
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array.pop #=> 6
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array #=> [1, 2, 3, 4, 5]
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# 删除首部元素
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array.shift #=> 1
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array #=> [2, 3, 4, 5]
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# 检查元素是否存在与数组之中
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array.includes? 3 #=> true
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# 一种特殊语法，用来创建字符串数组或符号数组
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%w(one two three) #=> ["one", "two", "three"] : Array(String)
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%i(one two three) #=> [:one, :two, :three] : Array(Symbol)
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# 对于定义了`new`和`#<<`方法的类，可以用以下语法创建新对象
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set = Set{1, 2, 3} #=> [1, 2, 3]
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set.class #=> Set(Int32)
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# 以下代码与上方等同
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set = Set(typeof(1, 2, 3)).new
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set << 1
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set << 2
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set << 3
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# 哈希表类型(Hash)
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{1 => 2, 3 => 4}.class #=> Hash(Int32, Int32)
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{1 => 2, 'a' => 3}.class #=> Hash(Int32 | Char, Int32)
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# 必须为空哈希表指定类型
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{} # Syntax error
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{} of Int32 => Int32 # {}
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Hash(Int32, Int32).new # {}
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# 可以使用键(key)快速查询哈希表
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hash = {"color" => "green", "number" => 5}
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hash["color"] #=> "green"
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hash["no_such_key"] #=> Missing hash key: "no_such_key" (KeyError)
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hash["no_such_key"]? #=> nil
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# 检查某一键哈希表中是否存在
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hash.has_key? "color" #=> true
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# 对于定义了`#[]=`方法的类，可以使用以下语法创建对象
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class MyType
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def []=(key, value)
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puts "do stuff"
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end
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end
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MyType{"foo" => "bar"}
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# 以上与下列代码等同
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tmp = MyType.new
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tmp["foo"] = "bar"
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tmp
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# 范围类型(Range)
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1..10 #=> Range(Int32, Int32)
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Range.new(1, 10).class #=> Range(Int32, Int32)
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# 包含或不包含端点
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(3..5).to_a #=> [3, 4, 5]
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(3...5).to_a #=> [3, 4]
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# 检查某一值是否在范围内
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(1..8).includes? 2 #=> true
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# 元组类型(Tuple)
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# 元组类型尺寸固定，不可变，储存在栈中
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# 元组可以有不同类型的对象组成
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{1, "hello", 'x'}.class #=> Tuple(Int32, String, Char)
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# 使用下标访问元组
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tuple = {:key1, :key2}
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tuple[1] #=> :key2
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tuple[2] #=> syntax error : Index out of bound
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# 将元组中的元素赋值给变量
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a, b, c = {:a, 'b', "c"}
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a #=> :a
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b #=> 'b'
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c #=> "c"
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# 命名元组类型(NamedTuple)
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tuple = {name: "Crystal", year: 2011} # NamedTuple(name: String, year: Int32)
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tuple[:name] # => "Crystal" (String)
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tuple[:year] # => 2011 (Int32)
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# 命名元组的键可以是字符串常量
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{"this is a key": 1} # => NamedTuple("this is a key": Int32)
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# 过程类型(Proc)
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# 过程代表一个函数指针，以及可选的上下文(闭包)
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# 过程通常使用字面值创建
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proc = ->(x : Int32) { x.to_s }
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proc.class # Proc(Int32, String)
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# 或者使用`new`方法创建
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Proc(Int32, String).new { |x| x.to_s }
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# 使用`call`方法调用过程
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proc.call 10 #=> "10"
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# 控制语句(Control statements)
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if true
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"if 语句"
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elsif false
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"else-if, 可选"
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else
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"else, 同样可选"
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end
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puts "可以将if后置" if true
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# 将if作为表达式
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a = if 2 > 1
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3
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else
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4
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end
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a #=> 3
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# 条件表达式
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a = 1 > 2 ? 3 : 4 #=> 4
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# `case`语句
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cmd = "move"
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action = case cmd
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when "create"
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"Creating..."
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when "copy"
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"Copying..."
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when "move"
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"Moving..."
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when "delete"
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"Deleting..."
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end
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action #=> "Moving..."
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# 循环
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index = 0
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while index <= 3
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puts "Index: #{index}"
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index += 1
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end
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# Index: 0
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# Index: 1
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# Index: 2
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# Index: 3
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index = 0
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until index > 3
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puts "Index: #{index}"
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index += 1
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end
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# Index: 0
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# Index: 1
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# Index: 2
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# Index: 3
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# 更好的做法是使用`each`
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(0..3).each do |index|
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puts "Index: #{index}"
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end
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# Index: 0
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# Index: 1
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# Index: 2
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# Index: 3
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# 变量的类型取决于控制语句中表达式的类型
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if a < 3
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a = "hello"
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else
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a = true
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end
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typeof a #=> (Bool | String)
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if a && b
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# 此处`a`与`b`均为Nil
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end
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if a.is_a? String
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a.class #=> String
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end
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# 函数(Functions)
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def double(x)
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x * 2
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end
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# 函数(以及所有代码块)均将最末尾表达式的值作为返回值
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double(2) #=> 4
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# 在没有歧义的情况下，括号可以省略
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double 3 #=> 6
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double double 3 #=> 12
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def sum(x, y)
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x + y
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end
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# 使用逗号分隔参数
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sum 3, 4 #=> 7
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sum sum(3, 4), 5 #=> 12
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# yield
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# 所有函数都有一个默认生成、可选的代码块(block)参数
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# 在函数中可以使用yield调用此代码块
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def surround
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puts '{'
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yield
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puts '}'
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end
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surround { puts "hello world" }
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# {
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# hello world
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# }
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# 可将代码块作为参数传给函数
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# "&" 表示对代码块参数的引用
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def guests(&block)
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block.call "some_argument"
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end
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# 使用星号"*"将参数转换成元组
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def guests(*array)
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array.each { |guest| puts guest }
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end
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# 如果函数返回数组，可以将其解构
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def foods
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["pancake", "sandwich", "quesadilla"]
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end
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breakfast, lunch, dinner = foods
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breakfast #=> "pancake"
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dinner #=> "quesadilla"
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# 按照约定，所有返回布尔值的方法都以问号结尾
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5.even? # false
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5.odd? # true
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# 以感叹号结尾的方法，都有一些破坏性(destructive)行为，比如改变调用接收者(receiver)
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# 对于某些方法，带有感叹号的版本将改变调用接收者，而不带有感叹号的版本返回新值
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company_name = "Dunder Mifflin"
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company_name.gsub "Dunder", "Donald" #=> "Donald Mifflin"
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company_name #=> "Dunder Mifflin"
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company_name.gsub! "Dunder", "Donald"
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company_name #=> "Donald Mifflin"
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# 使用`class`关键字来定义类(class)
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class Human
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# 类变量，由类的所有实例所共享
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@@species = "H. sapiens"
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# `name`的类型为`String`
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@name : String
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# 构造器方法(initializer)
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# 其中@name、@age为简写，相当于
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#
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# def initialize(name, age = 0)
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# @name = name
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# @age = age
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# end
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#
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# `age`为可选参数，如果未指定，则使用默认值0
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def initialize(@name, @age = 0)
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end
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# @name的setter方法
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def name=(name)
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@name = name
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end
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# @name的getter方法
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def name
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@name
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end
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# 上述getter与setter的定义可以用property宏简化
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property :name
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# 也可用getter与setter宏独立创建getter与setter
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getter :name
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setter :name
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# 此处的`self.`使`say`成为类方法
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def self.say(msg)
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puts msg
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end
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def species
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@@species
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end
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end
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# 将类实例化
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jim = Human.new("Jim Halpert")
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dwight = Human.new("Dwight K. Schrute")
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# 调用一些实例方法
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jim.species #=> "H. sapiens"
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jim.name #=> "Jim Halpert"
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jim.name = "Jim Halpert II" #=> "Jim Halpert II"
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jim.name #=> "Jim Halpert II"
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dwight.species #=> "H. sapiens"
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dwight.name #=> "Dwight K. Schrute"
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# 调用类方法
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Human.say("Hi") #=> 输出 Hi ，返回 nil
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# 带有`@`前缀的变量为实例变量
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class TestClass
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@var = "I'm an instance var"
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end
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# 带有`@@`前缀的变量为类变量
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class TestClass
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@@var = "I'm a class var"
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end
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# 首字母大写的变量为常量
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Var = "这是一个常量"
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Var = "无法再次被赋值" # 常量`Var`已经被初始化
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# 在crystal中类也是对象(object)，因此类也有实例变量(instance variable)
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# 类变量的定义由类以及类的派生类所共有，但类变量的值是独立的
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# 基类
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class Human
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@@foo = 0
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def self.foo
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@@foo
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end
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def self.foo=(value)
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@@foo = value
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end
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end
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# 派生类
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class Worker < Human
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end
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Human.foo #=> 0
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Worker.foo #=> 0
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Human.foo = 2 #=> 2
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Worker.foo #=> 0
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Worker.foo = 3 #=> 3
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Human.foo #=> 2
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Worker.foo #=> 3
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module ModuleExample
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def foo
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"foo"
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end
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end
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# include <Module> 将模块(module)中的方法添加为实例方法
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# extend <Module> 将模块中的方法添加为类方法
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class Person
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include ModuleExample
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end
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class Book
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extend ModuleExample
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end
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Person.foo # => undefined method 'foo' for Person:Class
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Person.new.foo # => 'foo'
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Book.foo # => 'foo'
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Book.new.foo # => undefined method 'foo' for Book
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# 异常处理
|
||
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||
# 定义新的异常类(exception)
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||
class MyException < Exception
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end
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|
||
# 再定义一个异常类
|
||
class MyAnotherException < Exception; end
|
||
|
||
ex = begin
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raise MyException.new
|
||
rescue ex1 : IndexError
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||
"ex1"
|
||
rescue ex2 : MyException | MyAnotherException
|
||
"ex2"
|
||
rescue ex3 : Exception
|
||
"ex3"
|
||
rescue ex4 # 捕捉任何类型的异常
|
||
"ex4"
|
||
end
|
||
|
||
ex #=> "ex2"
|
||
|
||
```
|
||
|
||
## 参考资料
|
||
|
||
- [官方网站](https://crystal-lang.org/)
|
||
- [官方文档](https://crystal-lang.org/docs/overview/)
|
||
- [在线运行代码](https://play.crystal-lang.org/#/cr)
|
||
- [Github仓库](https://github.com/crystal-lang/crystal)
|