What does 'yield called out of block' mean in Ruby?

Question

I'm new to Ruby, and I'm trying the following:

mySet = numOfCuts.times.map{ rand(seqLength) }

but I get the 'yield called out of block' error. I'm not sure what his means. BTW, this question is part of a more general question I asked here.

are you using jruby or mri ruby ? – Sam Saffron Sep 23 '08 at 05:03 — Sam Saffron, Sep 23 '08 at 05:03

user11318 · Accepted Answer · 2008-09-23T05:21:56.967

9

The problem is that the times method expects to get a block that it will yield control to. However you haven't passed a block to it. There are two ways to solve this. The first is to not use times:

mySet = (1..numOfCuts).map{ rand(seqLength) }

or else pass a block to it:

mySet = []
numOfCuts.times {mySet.push( rand(seqLength) )}

edited Sep 23 '08 at 05:21

answered Sep 23 '08 at 05:06

user11318

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you want a ) after numOfCuts there :) ( and that will have duplicates ) – Kent Fredric Sep 23 '08 at 05:20
Oops, fixed. And I was just trying to fix the API error, not the logic error. – user11318 Sep 23 '08 at 05:22
What exactly is a block in Ruby? – Esteban Araya Sep 23 '08 at 05:27
I don't think I can give a better explanation of blocks than the one in http://www.rubycentral.com/book/tut_containers.html (which is a chapter of Programming Ruby). – user11318 Sep 23 '08 at 05:43

score 1 · Answer 2 · answered Sep 23 '08 at 05:03

1

if "numOfCuts" is an integer,

5.times.foo

is invalid

"times" expects a block.

5.times{   code here   }

answered Sep 23 '08 at 05:03

Kent Fredric

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score 1 · Answer 3 · answered Sep 23 '08 at 05:10

You're combining functions that don't seem to make sense -- if numOfCuts is an integer, then just using times and a block will run the block that many times (though it only returns the original integer:

irb(main):089:0> 2.times {|x| puts x}
0
1
2

map is a function that works on ranges and arrays and returns an array:

irb(main):092:0> (1..3).map { |x| puts x; x+1 }
1
2
3
[2, 3, 4]

I'm not sure what you're trying to achieve with the code - what are you trying to do? (as opposed to asking specifically about what appears to be invalid syntax)

score 1 · Answer 4 · answered Sep 23 '08 at 13:01

Bingo, I just found out what this is. Its a JRuby bug.

Under MRI

>> 3.times.map
=> [0, 1, 2]
>>

Under JRuby

irb(main):001:0> 3.times.map
LocalJumpError: yield called out of block
    from (irb):2:in `times'
    from (irb):2:in `signal_status'
irb(main):002:0>

Now, I don't know if MRI (the standard Ruby implementation) is doing the right thing here. It probably should complain that this does not make sense, but when n.times is called in MRI it returns an Enumerator, whereas Jruby complains that it needs a block.

score 0 · Answer 5 · edited Sep 23 '10 at 21:15

0

Integer.times expects a block. The error message means the yield statement inside the times method can not be called because you did not give it a block.

As for your code, I think what you are looking for is a range:

(1..5).map{ do something }

Here is thy rubydoc for the Integer.times and Range.

edited Sep 23 '10 at 21:15

horseyguy

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answered Sep 23 '08 at 05:11

jop

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What does 'yield called out of block' mean in Ruby?

5 Answers5