Ruby meta programming 3(closure)

lantianjialiang

于 2016-08-18 12:55:24 发布

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分类专栏： ruby 文章标签： ruby meta

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本文通过Ruby代码示例介绍了闭包的概念及其工作原理，包括闭包如何捕获并记住其外部作用域中的变量状态，展示了不同场景下闭包的应用，如延迟计算税收等。

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# closure
10.times{ |i| print("=")}
puts("closure")
x = "hello world"

ablock = Proc.new { puts( x ) }

def aMethod( aBlockArg )
    x = "goodbye"
    aBlockArg.call
end

puts( x )
ablock.call
#this will output "hello world", because when the ablock is create, the value of x is "hello world"
aMethod( ablock )
ablock.call
puts( x )

def calcTax( taxRate ) 
   return lambda{ 
      |subtotal| 
      subtotal * taxRate 
      }  
end 

# create two closure, the taxRate is 0.1, then the returned block accept one argument as subtotal
salesTax = calcTax( 0.10 ) 
vat = calcTax( 0.175 ) 

print( "Tax due on book = ") 
print( salesTax.call( 10 ) )     #<= prints: 1.0 

print( "\nVat due on DVD = ") 
print( vat.call( 10 ) ) 

# local variable will not effect the block argument x
x = 3000 

c3 = lambda{  
   |x| 
   return x + 100   
} 

someval=1000 
someval=c3.call(someval); 
puts("\n" + someval.to_s) 
someval=c3.call(someval); puts(someval)  
puts( x )