Ruby4 Blocks and Exceptions

Block 代码块

1. Block是一个参数
2. 匿名参数
3. Callback
4. 使用do/en或者{}来定义

{puts 'hello'}

Demo:

# block usage def hello     puts 'hello method start'     yield     yield     puts 'hello method end' end  hello {puts 'i am in block'}  #output  hello method start i am in block i am in block hello method end 

# yield with parameter def hello     puts 'hello method start'     yield('hello','world')     puts 'hello method end' end  hello {|x,y| puts "i am in block,#{x} #{y}"}  #output hello method start i am in block,hello world hello method end

# yield with paramter def hello name     puts 'hello method start'     result = "hello " + name     yield(result)     puts 'hello method end' end  hello('world'){|x| puts "i am in block,i got #{x}"}  #output hello method start i am in block,i got hello world hello method end

# build in methods ['cat', 'dog','frog'].each do |animal|     puts animal end puts '-' * 30 ['cat','dog','frog'].each{|animal| puts animal} #output cat dog frog ------------------------------ cat dog frog 

# build in methods 10.times do |t|     puts t end  puts '-' * 30 ('a'..'d').each { |char| puts char}  #output 0 1 2 3 4 5 6 7 8 9 ------------------------------ a b c d

# varibale scope  # before ruby2.0 x = 1 [1, 2, 3].each { |x| puts x} puts x # => x will be 3,which is incorrect  #output 1 2 3 1  如果是在ruby2之前的版本 那么外部的变量x会被改变

# varibale scope # 如果是2.0版本之后 puts x会报错 sum = 0 [1, 2, 3].each { |x| sum += x} puts sum # puts x    #output 6

# block return value class Array     def find         each do |value|             return value if yield (value)         end         nil     end end  puts [1, 2, 3].find { |x| x == 2 }  #output 2

# block as named parameter def hello name, &block     puts "hello #{name}, from method"     block.call(name) end  hello('world') {|x| puts "hello #{x} form block"}  #output hello world, from method hello world form block

# yield with parameter  def hello     puts 'hello method start'     yield('hello','world')     puts 'hello method end' end  hello {|x,y| puts "i am block ,#{x},#{y}"}  #output hello method start i am block ,hello,world hello method end

# block_given?  def hello     if block_given?         yield     else         puts 'hello from method'     end end  hello puts '-' * 30 hello {puts 'hello from block'}  #output hello from method ------------------------------ hello from block

# block can be closure  def counter     sum = 0     # 代码库接收了一个参数x 如果x没有定义那么x为1 然后 sum +=x     proc {|x| x = 1 unless x; sum +=x } end  c2 = counter puts c2.call(1) #1 puts c2.call(2)  puts c2.call(3)  # 这里 closure 为闭包  #  #output 1 3 6

# new method to create block  # name is required  hello = -> (name){"hello #{name}"} puts hello.call('world')  puts '-' * 30  # name is required hello3 = lambda {|name| "hello #{name}"} puts hello3.call('world')  puts '-' * 30  hello2 = proc {|name| "hello #{name}"} puts hello2.call puts hello2.call('world')   # lambda和proc区别 proc可以不传参数 lambda 更像是一个方法，必须传递参数 #output hello world ------------------------------ hello world ------------------------------ hello hello world

Exceptions 异常

All Exception inherited from Exception Class

所有异常都继承自Exception类

常见Exception

1. StandardError
2. SyntaxError
3. RuntimeError
4. ArgumentError
5. NameError
6. etc.

ruby抓取Exception

# exception  def hello name     raise name #抛出异常  end  hello # =>ArgumentError hello('world') # =>RuntimeError

# exception catch  def hello     raise end  begin     hello rescue RuntimeError     puts 'got it' end

# exception catch  def hello     raise end  begin     hello rescue => e #出现异常捕获给e     puts "catch exception with name :#{e.class}" else #没有发生异常     # ... ensure #确保不论有没有发生异常     # ... end