question about passing an array iterator instance to a block

I was always under assumption that the block accepts the return value of the iterator as the argument to the block, but look at this: do | i |       puts i end

I expect i to be an array instance with 500 indexes all will nil values. However, what it returns is indeed an array with 500 indexes all with nil values BUT before it returns that array instance, the block appears to execute 500 times passing an actual integer value into the block incrementing by 1 each time. I dont understand why this is happening.

thanks for response

Because 'puts()' always return nil. It just generates STDOUT output.

thanks for response but that was just an example and not really what my question was about.

Perhaps this is a better example: do |id|

?> "'#{(id + 1).to_s.rjust(2,"0")}'"


=> ["'01'", "'02'", "'03'", "'04'", "'05'", "'06'", "'07'", "'08'", "'09'", "'10'"]

Why is "id" not the array instance. It obviously is an integer. Otherwise this would have failed with (id +1).

I don’t understand Why are you expecting an Array??

new(size=0, obj=nil)click to toggle source


new(size) {|index| block }

Returns a new array. In the first form, the new array is empty. In the second it is created with sizecopies of obj (that is, size references to the same obj). The third form creates a copy of the array passed as a parameter (the array is generated by calling to_ary on the parameter). In the last form, an array of the given size is created. Each element in this array is calculated by passing the element’s index to the given block and storing the return value.

There must be code inside like that:

if block_given?

yield index


You know what your completely right. The block only will take what the yield method returns to it. So apparently when instantiating an array with that first argument setting a size limit for array, the constructor contains a yield method which yields each iteration of that size limit. And then the return value is passed back to the resutlt of the yield and that value is then idnexed into the array until the size limit has been reached.

That wouldn't do the setting of the values in the array. Maybe:

if block_given?   size.times { |index| self << yield index } end

or, if it already needs to loop over it to initialize the slot:

size.times do |index|   # do other initialization   self << yield(index) if block_given? end