深入讲解Ruby中Block代码快的用法
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2021-01-02
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深入讲解深入讲解Ruby中中Block代码快的用法代码快的用法
Block
定义定义
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 <NameError>
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
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