我是一个对Ruby新手,正在进行一个涉及使用它的项目。Go语言提供了defer
语句,我想知道如何在Ruby中复制这个功能。
示例:
dst, err := os.Create(dstName)
if err != nil {
return
}
defer dst.Close()
我是一个对Ruby新手,正在进行一个涉及使用它的项目。Go语言提供了defer
语句,我想知道如何在Ruby中复制这个功能。
示例:
dst, err := os.Create(dstName)
if err != nil {
return
}
defer dst.Close()
在Ruby中,没有defer
语句的适当等价物,但是如果您希望确保执行特定的代码块,可以使用ensure
语句。不同之处在于,您不能像defer
那样堆叠代码块,但结果是相同的。
在一个块内
begin
# ...
ensure
# This code will be executed even if an exception is thrown
end
用一种方法
def foo
# ...
ensure
# ...
end
Object#ensure是一个可选的代码块最终闭合关键字,通常在该块中还包含rescue关键字。无论控制流是否转到rescue块,ensure块中的代码都保证会被执行。
这段代码本身没有这样的语句,但是你可以使用元编程来实现这个功能。
module Deferable
def defer &block
@defered_methods << block
end
def self.included(mod)
mod.extend ClassMethods
end
module ClassMethods
def deferable method
original_method = instance_method(method)
define_method(method) do |*args|
@@defered_method_stack ||= []
@@defered_method_stack << @defered_methods
@defered_methods = []
begin
original_method.bind(self).(*args)
ensure
@defered_methods.each {|m| m.call }
@defered_methods = @@defered_method_stack.pop
end
end
end
end
end
class Test
include Deferable
def test
defer { puts "world" }
puts "hello"
end
def stacked_methods str
defer { puts "and not broken" }
defer { puts "at all" }
puts str
test
end
def throw_exception
defer { puts "will be executed even if exception is thrown" }
throw Exception.new
end
deferable :test
deferable :stacked_methods
deferable :throw_exception
end
示例调用:
t = Test.new
t.test
# -> Output:
# hello
# world
t.stacked_methods "stacked methods"
# -> Output:
# stacked methods
# hello
# world
# and not broken
# at all
t.throw_exception
# -> Output:
# will be executed even if exception is thrown
# deferable.rb:45:in `throw': uncaught throw #<Exception: Exception> (UncaughtThrowError)
# from deferable.rb:45:in `throw_exception'
# from deferable.rb:18:in `call'
# from deferable.rb:18:in `block in deferable'
# from deferable.rb:59:in `<main>'