Putting #size-based implementations in abstract Collection subclasses negates the lazy collection benefit and still penalizes non-abstract direct Collection subclasses like CharacterSet and any user-defined direct Collection subclass implemented using composition with forwarding to a concrete collection. If the default linear complexity of #size and #isEmpty bothers you so much, make #size a subclassResponsiblity like #do: instead of suddenly penalizing collections whose authors actually did the right thing by providing a non-linear #size implementation.

> Sent: Friday, October 21, 2016 at 11:26 PM
> From: "Eliot Miranda" <eliot.miranda at gmail.com>
> To: "The general-purpose Squeak developers list" <squeak-dev at lists.squeakfoundation.org>
> Subject: Re: [squeak-dev] Re: The defaullt implementation of isEmpty might do too much work
>
> Hi Monty,
> 
>     what happens if you add an isEmpty implement ration based in size to SequenceableCollection?
> 
> _,,,^..^,,,_ (phone)
> 
> > On Oct 21, 2016, at 3:59 PM, monty <monty2 at programmer.net> wrote:
> > 
> > All non-trivial collections implement #size or inherit a custom implementation, usually just as a return of an inst var. Your #do:-based one is 3x as slow in my tests, so you've now made #isEmpty slower for every collection that implements #size just to benefit ones whose careless authors didn't and so the implementors of lazy collections have one fewer message to override.
> > 
> > Do not do this. People already avoid #ifEmpty: and related messages where performance matters and shouldn't have to avoid #isEmpty too.
> > 
> 
>