[swift-evolution] [Pitch] String prefix operator

[Xiaodi Wu]

On Sat, Jun 18, 2016 at 4:50 PM, Michael Peternell via swift-evolution <
swift-evolution at swift.org> wrote:

>
> > Am 17.06.2016 um 07:45 schrieb Charlie Monroe via swift-evolution <
> swift-evolution at swift.org>:
> >
> > Motivational example:
> >
> > var urlString = self.urlString
> > if urlString.hasPrefix("//") {
> >       urlString = "http:" + urlString // urlString needs to be typed
> twice
> > }
> >
> > While there is currently an easy way to append string using +=, there is
> no shortcut for prefixing a string. What I propose is adding a =+ operator
> for prefixing the string:
> >
> > urlString =+ "http:"
> >
> > Would anyone else find it useful?
>
> No. What I would find useful though, is to recognize that addition is not
> string concatenation. There is a strong convention in mathematics that the
> "+" symbol should only be used for operations that are commutative. String
> concatenation is not commutative. (There are more conventions regarding
> "+", but all of them are respected by numbers, vectors, complex numbers,
> quaternions, or matrices - just to name a few.)
>
> I would like to have a different operator for string concatenation.


I don't see how this would measurably improve Swift code. IIUC, much of the
problem with `+` and strings arises from implicit conversions that don't
happen in Swift. It's not even possible to write a generic algorithm that
accidentally confuses arithmetic `+` and string concatenation `+`, since
you would have to retroactively conform strings and numeric types to a
nonsensical protocol of your own making.


> Maybe "~~" or "++"? Now that the prefix and postfix operators for numbers
> ("++" and "--") are removed from Swift 3, "++" could be used for string
> concatenation.
>
> -Michael
>
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