On Fri, Mar 18, 2016 at 5:19 PM, Ted F.A. van Gaalen via swift-evolution < swift-evolution@swift.org> wrote:
On Chris’s advice, I’ve spawned this into a new discussion topic, for
which the base could be
part of what I wrote in relation to SE-0007.
Hello Patrick
as I wrote:
As a result of removing the classical for loop it is to be expected that
lot of people might consider thinking twice about switching to Swift, If
they have to live without (or cumbersome work around) language elements
that have proven to be very useful for at least a few decades...
I also find it of the most importance to keep Swift accessible for all
kinds of programmers
from starters to academic.
Graig Federighi said
*We think it should be everywhere and used by everyone.*
I subscribe to that.
-TedvG
On 18.03.2016, at 22:04, Patrick Gili <gili.patrick.r@gili-labs.com> > wrote:
Hi Ted,
I don't think many of us that are active on this mailing list had the
opportunity to provide feedback on this proposal review. I very much agree
with you on many points that you bring up below. I have spent a lot of time
scratching my head wondering why it was so important to remove certain
syntax from Swift, such as C-style loops, unary increment, and unary
decrement. Leaving them there increases compatibility of C code with Swift,
and leaving them there keeps them opt-in. If you don't want to use it, you
don't have to. However, the changes definitely force developers to use
newer syntax, which runs contrary to the "opt-in philosophy" that the core
team has impressed on the community.
I'm going to play devil's advocate though. Will the tools for Swift 3
automatically make the necessary changes to source to comply with the new
syntax? If so, is it so bad? I've been using the C language and all of its
variants for more than 32 years. Hence, it is easier on my eyes and brain
if there is some compatibility there. Personally, I think leaving this
syntax in the language eases migration. Although, I've been learning so
many new languages over the last decade that it seems to matter less with
time. However, I can't seem for the millions of developers that write code
for OS X and iOS.
Cheers,
-Patrick
On Mar 18, 2016, at 4:28 PM, Ted F.A. van Gaalen via swift-evolution < > swift-evolution@swift.org> wrote:
As most colleagues (that's what I think you all are, spanning two
generations :o)
might have noticed, I am not exactly happy with the removal of the
classical
for-loop ( for ;; ) but the damage has been done, so I will soon
present a proposal for a better alternative. Working on it.
I find this matter very important.
I do not agree with the for-loop removal proposal authored by Erica Sadun,
Important:
I would like to emphasize again that what I write is not intended
personally.
Also I realize that I am a bit late on this subject, but that is because I
was not here back then.
I wil go through it point by point and try to explain why IMHO I think
this is not a good proposal.
---------------------
Evaluating proposal SE-0007
Remove C-style for-loops with conditions and incrementers
• Proposal: • Author(s): Erica Sadun
"The C-style for-loop appears to be a mechanical carry-over from C rather
than a genuinely Swift-specific construct."
Could you explain to me why what, in your view, is
- a "genuinely Swift-specific construct” ?
- "not very Swift-like" ?
- "Swift-typical” ?
"It is rarely used and not very Swift-like."
This is definitely not true.
The classical for loop is one of the most frequently used language
constructs in most programming languages.
"More Swift-typical construction is already available with for-in
statements and stride."
Except for collections, these are inconvenient, cumbersome and
inefficient "work arounds" as described later in my comments in this email.
"Removing for loops would simplify the language."
Removing screw drivers from a toolbox would indeed simplify the toolbox.
So would removing closures, classes, protocols etc. from Swift.
Simplification of a programming language can also have its disadvantages.
" And starve the most common use-points for -- and ++, which are already
due to be eliminated from the language."
"The value of this construct is limited and I believe its removal should
be seriously considered"
There absolutely is no need to remove the for ; ; and also ++ -- from the
language. These can perfectly well co-exist with other language elements of
Swift. If you don't want to use them, that's fine, but for most people out
there who still want to use the for ;; and ++ -- .
"Swift design supported a shallow learning curve using familiar constants
and control structures.
The for-loop mimics C and limits the effort needed to master this control
flow."
Yes indeed. It mimics C and also the for-loop or its equivalent in more
that 20 other programming languages.
*"Disadvantages of For Loops*
1 Both for-in and stride provide equivalent behavior using Swift-coherent
approaches without being tied to legacy terminology”
Most language elements in Swift ARE legacy, and that's ok, so one does not
have to re-invent the wheel again.
"2 There is a distinct expressive disadvantage in using for-loops
compared to for-in in succinctness"
What makes you think so?
"3 for-loop implementations do not lend themselves to use with
collections and other core Swift types.”
Agreed if it concerns collections. However, they can. Of course, it is
much easier and more readable to use e.g. 'for item in items" for
collections.
Please enlighten me: what "other core-Swift-types" do you refer to?
"4 The for-loop encourages use of unary incrementors and decrementors,
which will be soon removed from the language."
Although the majority of programmers like the ++ and -- operators, I do
manage to understand why some do not like it. However ++ and -- are very
well suited for classical for-loops, in fact they even make them more
readable... Like so:
1. for i = 0; i < iterations; i++ { ...}
or
2. for i = 0; i < iterations; i += 1 { ...}
It looks like the first example is more readable. But yes, if it were
that the ++ -- would have remained in Swift, and also the classical
for-loop, using ++ and -- should probably restricted to be used in
for-loops only.
"5 The semi-colon delimited declaration offers a steep learning curve
from users arriving from non C-like languages."
IMHO, this is utter nonsense. Even from those coming from other languages
as C++, C, if a mere three arguments separated by two semicolons are "a
steep learning curve" ? Then what to think about using closures, lambda's,
classes, inheritance, functional programming, protocols etc. ?
*"Impact on existing code*
A search of the Apple Swift codebase suggests this feature is rarely used."
A search of the Apple Swift codebase is not representative, because the
scope of this search encompasses only source code made by users of the
programming language Swift, which is partly still under further
development. Faithfully representative would it be to search in a wider
perspective, which should include source code written in variety of
programming languages like Objective-C, Java, C#, C++, C, PHP , Ruby, Go,
Perl, Javascript, Dart, V. Basic, Pascal, PL/1, Cobol, Rexx. Most of this
languages have implemented the for-loop (or equivalent) . Undoubtedly if
one would do a search for for-loop in these languages it would become clear
that the for-loop is heavily used.
As a result of removing the classical for loop it is to be expected that
lot of people might consider thinking twice about switching to Swift, If
they have to live without (or cumbersome work around) language elements
that have proven to be very useful for at least a few decades...
How do you arrive at such a conclusion? In this perspective, Erica, I am
very much interested to know if you have practical experience with using
other programming languages than Objective C and Swift. Have you built
solid applications with other systems, IDEs and languages? Also, did you
consult programmers working with other well established languages?
"Community members of the Swift-Evolution mail list confirm that it does
not feature in many pro-level apps and can be worked around for those few
times when for-loops do pop up."
If one browses through the App Store, one might notice that most apps work
with collections (e.g. customers, addresses, shopping items, videos,
songs. etc.) For these kind of applications, the for-in-collection
statement in Swift is great and well catering for these requirements. The
result of this is, that the majority of Swift developers will not be aware
and not miss the classical for-loop (or a new Swift equivalent for it at
all) simply because they do not need it.
However, for those that make scientific, engineering, statistical,
technical and game apps, the lack of a simple but versatile iteration
statement, which in most cases can be compiled down to a simple and very
fast assembler loop is nothing less than a disaster.
E.g. For the purpose of performance testing, in an Apple TV SceneKit app I
am currently building, I did replace replace the classical for-loop by a
"for in x.stride(..." for coordinate calculations. Performance dropped
to about 45%, this is unacceptable. The compiler cannot get rid of this.
Working with a collection based for-in will nearly always be twice as slow,
for the simple reason that the contents of the collection it has to process
are by definition unpredictable.
In your proposal you offered the following example. I do not know where
you found this horrible piece of code. However, in this case it is not the
for-loop that is so bad, but the complete function. There are many better
and well structured classical for-loops to be found everywhere. I cannot
deflect my impression that you might have selected this particularly bad
example solely to amplify your proposal's case.
"
char *blk_xor(char *dst, const char *src, size_t len)
{
const char *sp = src;
for (char *dp = dst; sp - src < len; sp++, dp++)
*dp ^= *sp;
return dst;
}
"
Again, this is a extremely bad C Example, infested with (at least to me)
unclear pointer usage. (Luckily in Swift there are (or should be) no
pointers) Somewhere in this messy example, yes, a for-loop can be found.
Notice that the for-loop itself is relatively simple and straightforward.
Also, the fact that this for-loop deploys two value incrementors instead of
one, is in this particular context not really all that bad.
In my opinion, the Swift equivalent you offer, does not look much better:
"
func blk_xor(dst: UnsafeMutablePointer<CChar>, src:
UnsafePointer<CChar>, len: Int) -> UnsafeMutablePointer<CChar> {
for i in 0..<len {
dst[i] ^= src[i]
}
return dst
}
A search of github's Swift gists suggests the approach is used primarily
by those new to the language with minimal language skills and is abandoned
as language mastery is achieved.
"
Another subjective assumption and almost insulting for those, often with
years of experience, who deploy the classical for-loop intensively and
really knowing what they are doing.
My conclusion:
Although the proposal has been accepted. I would like to see it withdrawn
because the arguments brought forward are highly subjective,
not thoroughly analyzed and in some cases even false.
Furthermore, a proposal should be based on facts, not assumptions.
Kind Regards
TedvG.
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