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fetch 

        # Array.fetch

(from ruby core)
---
    array.fetch(index) -> element
    array.fetch(index, default_value) -> element
    array.fetch(index) {|index| ... } -> element

---

Returns the element at offset  `index`.

With the single Integer argument `index`, returns the element at offset
`index`:
    a = [:foo, 'bar', 2]
    a.fetch(1) # => "bar"

If `index` is negative, counts from the end of the array:
    a = [:foo, 'bar', 2]
    a.fetch(-1) # => 2
    a.fetch(-2) # => "bar"

With arguments `index` and `default_value`, returns the element at
offset `index` if index is in range, otherwise returns `default_value`:
    a = [:foo, 'bar', 2]
    a.fetch(1, nil) # => "bar"

With argument `index` and a block, returns the element at offset `index`
if index is in range (and the block is not called); otherwise calls the
block with index and returns its return value:

    a = [:foo, 'bar', 2]
    a.fetch(1) {|index| raise 'Cannot happen' } # => "bar"
    a.fetch(50) {|index| "Value for #{index}" } # => "Value for 50"

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