Saturday, November 14, 2015

Where “where” May Be Used in Swift

Marcin Krzyżanowski:

The fact is you can use where keyword in a case label of a switch statement, a catch clause of a do statement, or in the case condition of an if, while, guard, for-in statement, or to define type constraints.

There are no Python-style list or dictionary comprehensions, though.

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"There are no Python-style list or dictionary comprehensions, though."

Collections have map and filter methods. Not sure how efficient they are when chained together (ideally you don't want an entire temp array being generated inbetween each call), but eh. The biggest complaint is that applying `map` to a dictionary doesn't return a new dictionary but an array, though I imagine there's already a bunch of Radar tickets on that so hopefully it'll get sorted at some point.


OTOH, what's constantly being missed in this multitude of trees is the basic insanity of both Python and Swift sprouting all these duplicative doodads in the first place: `for` and `where`, which almost but not quite avoid the need for `map` and `filter`; and `map` and `filter`, which almost but not quite eliminate the need for `for` and `where`. (And in Python's case yet another option, ``, which almost but not quite duplicates all the others and vice-versa.)

A good, parsimonious language design would pick one form (preferably the one that's the most composable), make sure it covers all of the relevant use cases, and blow away all the others, then get on with far more productive business of building interesting new layers of capability on top of that settled foundation. But mainstream language designers have this bad habit of fixating on primitive trivialities, so that by the time they're done creating a vast ingenious rats' nest out of those, nobody involved - language developers or language users - has the time or brain capacity left to manage anything more.



p.s. My Swift duh of the day: case is Foo, is Bar works perfectly while catch is Foo, is Bar won't even compile. Go fig.

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