[swift-evolution] Strings in Swift 4
david at alkaline-solutions.com
Mon Feb 6 14:39:58 CST 2017
> On Feb 6, 2017, at 10:26 AM, Ted F.A. van Gaalen via swift-evolution <swift-evolution at swift.org> wrote:
> Hi Dave,
> Oops! yes, you’re right!
> I did read again more thoroughly about Unicode
> and how Unicode is handled within Swift...
> -should have done that before I write something- sorry.
> How about this solution: (if I am not making other omissions in my thinking again)
> -Store the string as a collection of fixed-width 32 bit UTF-32 characters anyway.
> -however, if the Unicode character is a grapheme cluster (2..n Unicode characters),then
> store a pointer to a hidden child string containing the actual grapheme cluster, like so:
> 1: [UTF32, UTF32, UTF32, 1pointer, UTF32, UTF32, 1pointer, UTF32, UTF32]
> | |
> 2: [UTF32, UTF32] [UTF32, UTF32, UTF32, ...]
> whereby (1) is aString as seen by the programmer.
> and (2) are hidden child strings, each containing a grapheme cluster.
The random access would require a uniform layout, so a pointer and scalar would need to be the same size. The above would work with a 32 bit platform with a tagged pointer, but would require a 64-bit slot for pointers on 64-bit systems like macOS and iOS.
Today when I need to do random access into a string, I convert it to an Array<Character>. Hardly efficient memory-wise, but efficient enough for random access.
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