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:

Array.new(500) 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

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  • Valery Kvon at Feb 25, 2012 at 7:56 pm

    On 25.02.2012, at 23:41, John Merlino wrote:

    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:

    Array.new(500) 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.
    Because 'puts()' always return nil. It just generates STDOUT output.

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  • John Merlino at Feb 25, 2012 at 8:08 pm
    thanks for response but that was just an example and not really what
    my question was about.

    Perhaps this is a better example:
    Array.new(10) do |id|
    ?> "'#{(id + 1).to_s.rjust(2,"0")}'"
    end
    => ["'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).
    On Feb 25, 2:55 pm, Valery Kvon wrote:
    On 25.02.2012, at 23:41, John Merlino wrote:

    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:
    Array.new(500) 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.
    Because 'puts()' always return nil. It just generates STDOUT output.
    --
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  • Valery Kvon at Feb 25, 2012 at 8:22 pm

    On 26.02.2012, at 0:07, John Merlino wrote:

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

    Perhaps this is a better example:
    Array.new(10) do |id|
    ?> "'#{(id + 1).to_s.rjust(2,"0")}'"
    end
    => ["'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(array)
    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
    end

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  • John Merlino at Feb 25, 2012 at 8:42 pm
    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.
    On Feb 25, 3:15 pm, Valery Kvon wrote:
    On 26.02.2012, at 0:07, John Merlino wrote:

    thanks for response but that was just an example and not really what
    my question was about.
    Perhaps this is a better example:
    Array.new(10) do |id|
    ?>   "'#{(id + 1).to_s.rjust(2,"0")}'"
    end
    => ["'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(array)
    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
    end
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  • Dave Aronson at Feb 28, 2012 at 2:22 pm

    On Sat, Feb 25, 2012 at 15:15, Valery Kvon wrote:

    There must be code inside like that:

    if block_given?
    yield index
    end
    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

    -Dave

    --
    Dave Aronson:  Available Cleared Ruby on Rails Freelancer
    (NoVa/DC/Remote) -- see www.DaveAronson.com, and blogs at
    www.Codosaur.us, www.Dare2XL.com, www.RecruitingRants.com

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postedFeb 25, '12 at 7:41p
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