til/ruby/if-you-detect-none.md

If You Detect None

The Enumerable#detect method, which is synonymous with #find, can be given an optional argument, ifnone, that is called when nothing in the array meets the conditional in the block. Though I am not sure how this is practically useful and cannot find an example of it in use, this contrived example illustrates how it works.

# without the fallback behavior
> [2,4,6,8].detect { |x| x.odd? }
=> nil

# with a proc as an argument
> [2,4,6,8].detect(->{0}) { |x| x.odd? }
=> 0

The last example can also be written as:

> [2,4,6,8].detect(->{0}, &:odd?)
=> 0

And if you want to be really explicit:

> [2,4,6,8].detect(ifnone=->{0}, &:odd?)
=> 0