[swift-evolution] Change Request: Make myString.hasPrefix("") and myString.hasSuffix("") return true

[Bianca]

> Empty set is a subset of all sets.

True but all sets certainly do not _contain_ the empty set, which is what
might be confusing, as the word "contains" in the context of sets implies
that it's a member of the set of characters that make up a String.

On Tue, Jul 19, 2016 at 12:23 PM Charlie Monroe via swift-evolution <
swift-evolution at swift.org> wrote:

>
> > On Jul 19, 2016, at 6:17 PM, Ted F.A. van Gaalen via swift-evolution <
> swift-evolution at swift.org> wrote:
> >
> > 1.  return “false”  seems to me logically correct, because
> >     there is never an empty string in another string, and an empty
> string cannot contain another empty string, right?
>
> Empty set is a subset of all sets.
>
> Just like:
>
> let arr1: [String] = ["Hello", "Swift", "Evolution"]
> let arr2: [String] = []
> arr1.starts(with: arr2, isEquivalent: ==) // true
>
> >    This has worked very conveniently for NSString in ObjC for more than
> 20 years, why change it?
> >    Do you know of cases that were problematic with this convention?
> >
> >
> > 2  throw a runtime error when trying to do this:
> >    str.hasPrefix(“”)     //  also for hasSuffix,  str.contains etc.
> >
> > some in-line questions below.
> >
> > Kind Regards
> >
> > Ted
> >
> >
> > On 19.07.2016, at 16:31, Dave Abrahams <dabrahams at apple.com> wrote:
> >>
> >>
> >> on Tue Jul 19 2016, "Ted F.A. van Gaalen" <tedvgiosdev-AT-gmail.com>
> wrote:
> >>
> >>> Hi Dave
> >>>
> >>> “true” ? am I going nuts ? :o)
> >>>
> >>> var str = "Hello, playground"
> >>>
> >>> print( str.hasPrefix("”)) // case 1 : false
> >>>
> >>> print( str.hasSuffix("”)) // case 2 : false
> >>>
> >>> print("" == “a” )          // case 3 : false
> >>>
> >>> Currently, all cases above evaluate to “false”
> >>> i think that is correct,
> >>
> >> I don't know what to tell you.  It may seem intuitively correct to you,
> >> but others in the thread have laid out the reasons why it is not
> >> mathematically correct behavior.
> > Where? I couldn’t find any.
> >> One other way of rephrasing it: to get
> >> `false` for str.hasPrefix(""), you actually need special-case code in
> >> hasPrefix to check for the empty string,
> > again, maybe it should throw a run-time error instead.
> >
> >
> >> and the caller may well also
> >> need special-case code to handle the fact that the result is not
> >> mathematically consistent with other cases on the continuum.
> > In this context as “continuum” :
> >   are you referring to  “sets” or “collections” here?
> > what other cases?
> >
> >> Doing
> >> things that way doesn't work in practice for real programs.
> > please explain thank you, because I see no problems at
> > all with the current NSString-like evaluation…
> > I’d put an s.isEmpty() in front of it.
> >>
> >>> because:
> >>>
> >>> How can an empty string be a prefix or suffix value?
> >>> as there is no empty string present in a non-empty string.
> >>>
> >>> Note that if case 1 and case 2 would evaluate to “true”,
> >>> it would conflict with case 3.
> >>>
> >>> Can’t imagine that case 3 should in future also result in “true”
> >>>
> >>> ??
> >>>
> >>> -----
> >>>
> >>> Also I hope that changes to String functionality
> >>> for Swift 4 are not backward breaking changes
> >>> even the more for string handling, because Strings
> >>> are heavily used in most apps.
> >>>
> >>> I am firmly convinced that all future releases of Swift
> >>> should compile Swift 3 and higher source files without
> >>> any changes 100 % flawlessly! This prevents early diminishing
> >>> of Swift’s popularity, especially with those building large
> >>> codebases using Swift.
> >>>
> >>> I’ve started a thread about this a week ago,
> >>> however no one found this important enough to
> >>> share their opinions with me yet, or were too busy with
> >>> other subjects to do so.
> >>>
> >>> Increasingly I have dreams, me
> >>> programming complete apps in Smalltalk
> >>> and then automagically generate
> >>> an macOS, tvOS or iOS runtime app of it.
> >>>
> >>> (I have also dreams of this world becoming
> >>> a nice and peaceful placebut that is
> >>> beyond the context of this forum)
> >>>
> >>> Kind Regards
> >>> TedvG
> >>>
> >>> www.speyer.de
> >>>
> >>>> on Mon Jul 18 2016, Kevin Nattinger <swift-evolution at swift.org
> <mailto:swift-evolution at swift.org>> wrote:
> >>>>
> >>>>> I agree, true is definitely the expected behavior. In particular, it
> >>>>> seems absurd to me that `a.hasPrefix(b)` and `a.hasSuffix(b)` could
> be
> >>>>> false when `a == b` is true.
> >>>>
> >>>> I expect to be reworking Strings for Swift 4, and this is one of the
> >>>> many things we plan to address.
> >>>>
> >>>> --
> >>>> Dave
> >>>>
> >>>>
> >>>
> >>
> >> --
> >> Dave
> >
> > _______________________________________________
> > swift-evolution mailing list
> > swift-evolution at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-evolution
>
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>
-- 
Bianca
http://biancatamayo.me
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