(2010/09/17 20:10), Nikolai Weibull wrote:
> On Fri, Sep 17, 2010 at 13:00, Urabe Shyouhei <shyouhei / ruby-lang.org> wrote:
>> (2010/09/17 19:19), Nikolai Weibull wrote:
>>> Why doesn¡Çt Enumerable define a #last method that¡Çs analogous to #first?
>>
>> Simplest counterexample is [1].cycle.last
> 
> I wouldn¡Çt say that that example counters the validity of having #last
> in Enumerable.  I mean, sure, there¡Çs obviously no last element in
> this example, but neither can #all? be answered:
> 
> [1].cycle.all?{ |i| i == 1 }
> 
> even though it has an obvious answer.

OK, a bit more complicated example.

require "stringio"
s = StringIO.new "foobar"
e = s.enum_for :each_char
s.seek 6
e.last # => nil for your definition, but not sure if it should be?

The point is, an Enumerable's last may not exist for various reasons.