Ruby local variables in a for loop

Question

I would like to know if it is possible to set local variables in Ruby for loop.

More precisely I would like to have the for loop to behave like this:

tmp = 0
1.upto(5) { |i;tmp| puts i; tmp = i; } ; "tmp: #{tmp}"

The tmp variable should not be modified by what runs inside the foor loop.

Answer 1

You can introduce a new block for masking the outer variable

tmp = 0
for i in (1..5) do
  proc do |;tmp|
    puts i
    tmp = i
  end[]
end

This is awful. The difference between for and each is that the iteration variable in a for loop pollutes the outer scope .

x = []
# i has same scope as x
for i in (1..3)
  # closure captures i outside the loop scope, so...
  x << lambda { i }
end
# WAT
x.map(&:call) # [3, 3, 3]

x = []
(1..3).each { |i| x << lambda { i } }
# sanity restored
x.map(&:call) # [1, 2, 3]

Using my hack above to make your for act more like an each makes already confusing behavior even more confusing. Better to avoid for entirely.

Answer 2

我认为这是不可能的， for循环没有自己的作用域。