From: Siep Korteling <s.korteling@...>
Date: 2010-10-31T07:19:19+09:00
Subject: Re: Undocumented feature: Array#one? (ruby 1.9.2)

James Edward Gray II wrote in post #958258:
> On Oct 30, 2010, at 4:45 PM, Siep Korteling wrote:
>
>> In (my) ruby 1.9.2 class Array has an undocumented method #one? . It
>> takes no arguments and returns true if the array contains one element,
>> false otherwise. Is this something someone forgot to delete?
>
> $ ri -T Enumerable#one?
> Enumerable#one?
>
> (from ruby core)
> ------------------------------------------------------------------------------
>   enum.one? [{|obj| block }]   => true or false
>
> ------------------------------------------------------------------------------
>
> Passes each element of the collection to the given block. The method
> returns
> true if the block returns true exactly once. If the block is not
> given, one? will return true only if exactly one of the
> collection members is true.
>
>   %w{ant bear cat}.one? {|word| word.length == 4}   #=> true
>   %w{ant bear cat}.one? {|word| word.length > 4}    #=> false
>   %w{ant bear cat}.one? {|word| word.length < 4}    #=> false
>   [ nil, true, 99 ].one?                            #=> false
>   [ nil, true, false ].one?                         #=> true
>
> James Edward Gray II

Ah, it takes a block. That certainly makes more sense.

Thanks.

Siep

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