Ruby中Block代码快的使用深度解析

　　今天小编给大家分享一篇Ruby中Block代码快的使用深度解析，感兴趣的朋友跟小编一起来了解一下吧!

　　Block 定义

　　some_array.each { |value| puts value + 3 }

　　sum = 0

　　other_array.each do |value|

　　sum += value

　　puts value / sum

　　end

　　A block is somewhat like the body of an anonymous method

　　Block can take parameters

　　Block 只有被 method 调用时才会起作用，如果 method 中有参数，block 出现在最后面

　　Block 中的变量

　　如果 block 的本地变量的名字和 block 之外但是在同样 scope 里面的 变量名字一样，那他们两个是一样的。block 内变量的值会改变 block 外变量的值。

　　sum = 0

　　[1,2,3,4].each do |value|

　　sum += value

　　puts value / sum

　　end

　　puts sum # => 30

　　如果 block 中的变量只出现在 block 中，那么它只是 block 中本地变量，无法在 block 之外被引用。

　　sum = 0

　　[1,2,3,4].each do |value|

　　square = value * value

　　sum += square

　　end

　　puts sum # => 30

　　puts square # undefined local variable or method 'square' for main:Object

　　Parameters to a block are always local to a block, even if they have the same name as locals in the surrounding scope.

　　value = "some shape"

　　[1,2].each { |value| puts value }

　　puts value

　　# 1

　　# 2

　　# some shape

　　You can define a block-local variables by putting them after s semicolon in the block's parameter list

　　square = "some shape"

　　sum = 0

　　[1,2,3,4].each do |value; square|

　　square = value * value

　　sum += square

　　end

　　puts sum # 30

　　puts square # some shape

　　By making square block-local, values assigned inside the block will not affect the value of the variable with the same name in the outer scope.

　　Blocks for Transactions

　　You can use blocks to define a chunk of code that must be run under some kind of transnational control

　　class File

　　def self.open_and_process(*args)

　　f = File.open(*args)

　　yield f

　　f.close

　　end

　　end

　　File.open_and_process("testfile","r") do |file|

　　while line = file.gets

　　puts line

　　end

　　end

　　Blocks Can Be Objects

　　You can convert a block into an object, store it in variables, pass it around, and then invoke its code later.

　　如果 method 的最后一个参数前面有 & 符号 (&action), 那么当此 method 被调用时，Ruby 会找一个 code block, 这个 code block 被转换成 class Proc 的一个对象。

　　class ProcExample

　　def pass_in_block(&action)

　　@stored_proc = action

　　end

　　def use_proc(parameter)

　　@store_proc.call(parameter)

　　end

　　end

　　eg = ProcExample.new

　　eg.pass_in_block { |param| puts "The parameter is #{param}" }

　　eg.use_proc(99)

　　# => The parameter is 99

　　def create_block_object(&block)

　　block

　　end

　　bo = create_block_object { |param| puts "You called me with #{param}" }

　　bo.call 99 # => You called me with 99

　　bo.call "cat" # => You called me with cat

　　Ruby have two built-in methods that convert a block to an object: lambda and Proc.new

　　bo = lambda { |param| puts "You called me with #{param}" }

　　bo.call 99 # => You called me with 99

　　Blocks Can Be Closures

　　Closure: Variables in the surrounding scope that are referenced in a block remain accessible accessible for the life of that block and the life on any Proc object created from that block.

　　def n_times(thing)

　　lambda {|n| thing * n}

　　end

　　p1 = n_times(23)

　　p1.call(3) #=> 69

　　p2.call(4) #=> 92

　　def power_proc_generator

　　value = 1

　　lambda { value += value }

　　end

　　power_proc = power_proc_generator

　　puts power_proc.call # 2

　　puts power_proc.call # 4

　　lambda 表达式的另一种简写方式

　　lambda { |params| ... }

　　# 与下面的写法等价

　　-> params { ... }

　　# parmas 是可选的

　　proc1 = -> arg1, arg2 {puts "#{arg1} #{arg2}"}

　　proc1.call "hello", "world"

　　# => hello world

　　proc2 = -> { "Hello World" }

　　proc2.call # => Hello World

　　Block Parameter List

　　Blocks can take default values, splat args, keyword args and a block parameter

　　proc = -> a, *b, &block do

　　puts "a = #{a.inspect}"

　　puts "b = #{b.inspect}"

　　block.call

　　end

　　proc.call(1,2,3,4) {puts "in block"}

　　# a = 1

　　# b = [2,3,4]

　　# in block

　　以上就是Ruby中Block代码快的使用深度解析，想必都了解了吧，更多相关内容请继续关注武林技术频道。