> On Nov 16, 2017, at 2:52 AM, Gwendal Roué via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>> The optional itself will stand for the boolean needed by the filtering
>> operation.
>
> What I meant here is that "filterMap" can only click in a developer's mind if
> the the developer uses Optional as a Bool. When the closure returns nil, that
> nil stands for false in the filtering operation. When the closure returns a
> `some`, that some stands for true in the filtering operation.
>
> Put in another way: to properly explain "filterMap" to someone who already
> knows "filter", then you have to explain that optionals are used as booleans.
I disagree that you have to view Optionals as Booleans to understand filterMap
as proposed. Optionals naturally represent the idea of either a value, or
nothing. The filterMap operation runs a map that can filter stuff out. If you
filter something out, you end up with “nothing”, which is exactly what
returning nil means. So when I use filterMap, I map all the things I want to
let through, and I filter the rest out by letting nothing through.
-BJ
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