# Use of array shift and blocks

(Something a bit more basic than the other thread about the array shfit
bug!)

Given the following:

myArray=[“a”, “b”, “c”, “d”]
until myArray.empty?
myArray.shift { |letter|
puts letter
}
end

… I would expect the letters a, b, c and d to be printed to the
screen, but I don’t get anything (including no error message). Have I
misunderstood something about array shift and/or blocks?

Hi –

On Mon, 25 Sep 2006, Toby R. wrote:

end

… I would expect the letters a, b, c and d to be printed to the
screen, but I don’t get anything (including no error message). Have I
misunderstood something about array shift and/or blocks?

shift doesn’t take a block. You can write one but shift won’t call
it.

You could do this:

until array.empty?
puts array.shift
end

David

On 2006-09-24, Toby R. [email protected] wrote:

Given the following:
myArray=[“a”, “b”, “c”, “d”]
until myArray.empty?
myArray.shift { |letter|
puts letter
}
end

change the code to:
myArray=[“a”, “b”, “c”, “d”]
until myArray.empty?
letter = myArray.shift
puts letter
end

depesz

unknown wrote:

shift doesn’t take a block. You can write one but shift won’t call
it.

You could do this:

until array.empty?
puts array.shift
end

David

Many thanks David. I’m not sure I understand why shift doesn’t take a
block, but thanks for confirming it.

regards
Toby

Hi –

On Mon, 25 Sep 2006, Toby R. wrote:

David

Many thanks David. I’m not sure I understand why shift doesn’t take a
block, but thanks for confirming it.

I expect it’s because shifting is a (conceptually) atomic operation.
If you need to examine what got shifted, you can get the return value.
If you need to examine the newly-shortened array, you can examine it
directly. There’s really nothing for a block to do.

Consider, by way of contrast, something like String#sub, where you
find something and replace it with something – and you might want to
have a handle on the ‘something’, in the middle, so that you can
manipulate it to generate the eventual replacement string.

David