How to `break` a outside loop in closure (Proc, lambda)?

Question

loop { break } can work fine, but

block = Proc.new { break }
# or
# block = lambda { break }
loop(&block) # => LocalJumpError: break from proc-closure

Is it possible to break in a block variable ?

Update:

A example to explain more:

def odd_loop
    i = 1
    loop do
        yield i
        i += 2
    end
end

def even_loop
    i = 2
    loop do
        yield i
        i += 2
    end
end

# This work
odd_loop do |i|
    puts i
    break if i > 10
end

# This doesn't work
break_greater_10 = Proc.new do |i|
    puts i
    break if i > 10
end

odd_loop(&break_greater_10) # break from proc-closure (LocalJumpError)
even_loop(&break_greater_10) # break from proc-closure (LocalJumpError)

As my comprehension, Proc.new should work same as block (it can return a function from block), but I don't understand why can't break a loop.

P.S. Sorry for my bad english >~<

@Sergio See update, @tokland I know the different in Proc.new and lambda, I am asking break in closure — Steely Wing
– Steely Wing, Commented Mar 15, 2013 at 10:55

Pilo · Accepted Answer · 2015-02-05 15:54:25Z

7

To solve this problem you could

raise StopIteration

this worked for me.

answered Feb 5, 2015 at 15:54

Pilo

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1 Comment

Kelvin Over a year ago

+1 Not only does it work, it's actually used in an example in the ruby docs to halt a loop.

halfelf · Accepted Answer · 2013-03-15 10:14:28Z

3

To return from a block you can use the next keyword.

def foo
  f = Proc.new {next ; p 1}
  f.call
  return 'hello'
end

puts foo     # => 'hello' , without 1

answered Mar 15, 2013 at 10:14

halfelf

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3 Comments

Steely Wing Over a year ago

break a outside loop is different return from block

Steely Wing Over a year ago

In your case, you can use lambda and use return, I think next is not good for this (although it works)

Kelvin Over a year ago

This doesn't actually work to halt a loop as the OP asked.

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