我曾经编写类似 let 的表达式——具有词法范围。
所以我自己写了(悲伤,但它会因多线程而失败):
# Useful thing for replacing a value of
# variable only for one block of code.
# Maybe such thing already exist, I just not found it.
def with(dict, &block)
old_values = {}
# replace by new
dict.each_pair do |key, value|
key = "@#{key}"
old_values[key] = instance_variable_get key
instance_variable_set key, value
end
block.call
# replace by old
old_values.each_pair do |key, value|
instance_variable_set key, value
end
end
我在谷歌中搜索 ruby 的此类结构(可能是附加块定义),但找不到它。也许我失去了一些东西?在这种情况下,红宝石人使用什么?
PS:抱歉我的英语不好,你知道的。
UPD:我忘了提供用法示例:
@inst_var = 1
with :inst_var => 2 do
puts @inst_var
end
puts @inst_var
output:
2
1
An idea:
class Object
def let(namespace, &block)
namespace_struct = Struct.new(*namespace.keys).new(*namespace.values)
namespace_struct.instance_eval(&block)
end
end
message = let(language: "Lisp", year: "1958", creator: "John McCarthy") do
"#{language} was created by #{creator} in #{year}"
end
单值范围更明确,因为您在块参数中命名变量。这个抽象被称为as
, pipe
, into
, scope
, let
, peg
,...,凡是你能想到的,都是一样的:
class Object
def as
yield self
end
end
sum = ["1", "2"].map(&:to_i).as { |x, y| x + y } #=> 3
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