+1 to Haravikk's opinion, my thoughts exactly the same.
On 10.06.2016 15:18, Haravikk via swift-evolution wrote:
On 10 Jun 2016, at 07:25, Xiaodi Wu via swift-evolution
<[email protected] <mailto:[email protected]>> wrote:
* Swift is explicitly a C-family language. In most or all other C-family
languages, for loop statements allow specification of conditions for
exiting the loop but not for filtering. Therefore, Swift's use of `where`
is unprecedented and needs to be learned anew by every user of Swift.
Swift may have some similarities with C, but the last thing anyone should
want is for it to be bound to C as a language. Besides, the purpose of a
for in loop is to iterate over elements in a sequence, so filtering is very
much a useful thing to do so it’s hardly unprecedented, and it’s also a
fairly common thing to want to do.
* The word "where" does not consistently imply `break` or `continue`. In
current Swift, `where` implies `break` in the context of a `while` loop
and `continue` in the context of a `for` loop. Some users intuitively
guess the correct meaning in each context, while others guess the wrong
meaning. Therefore, the only way to learn for sure what `where` means in
any context is to read the rulebook. That, by definition, means that this
is unintuitive.
This is an argument for renaming the where keyword on for loops to be more
clear, or to somehow integrate continue/break to be more explicit about
what the developer intends for it to do.
* There are other ways to break from a loop or continue to the next
iteration without performance penalty. Nearly all of these serve more
general purposes than a `where` clause.
This isn’t really an argument against the where clause; the where clause is
useful for common, simple cases, so it’s not surprising if more
complex/unusual cases can’t (or can’t easily) be handled by it. This is for
the simple cases where this isn’t an issue.
Some of these (such as `if` or `guard`) would already be familiar to a
new user before they encounter loops, assuming a typical order for
learning a programming language. Many of these (such as filtering methods
on collections, or simply `if`) would be familiar to a user of another
C-family language. Therefore, the `where` clause provides no independent
utility, is not more discoverable than its alternatives, and is not
required for progressive disclosure of an important facility to a learner
(i.e. a simplified syntax for those who may not be ready for the advanced
concepts needed to use a more fully-featured alternative).
Simplification isn’t just for the new users; all you need to know with
where is that it’s a shorthand for guard X else { continue }, for many
people this is intuitive enough, but if there are enough for whom it isn’t
then again that’s an argument to tweak it to be more clear about what it
does, rather than remove it entirely.
The independent utility that it offers is being able to avoid if/guard
boilerplate at the start of your loop, but instead putting it on the same
line; in simple cases this can be nice and neat.
it has been used incorrectly by at least some users.
Every feature in every language "has been used incorrectly by at least some
users", should we just drop all programming languages? It’s not as if users
can’t make mistakes while using an inline if/guard condition. Again, this
an argument that the meaning isn’t implicit enough, which is just as well
served by tweaking the syntax than removing it.
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