Unexpected length of \r\n

ole · June 17, 2020, 7:20pm

tera:

import Foundation
("\u{0041}\u{0300}").contains("\u{0041}") // false
("\u{0041}\u{0300}").contains("\u{0300}") // true
interestingly here it is "false,true" rather than "true,true" in the foundation case

Nice find! The following is a guess as to why this is, I could be wrong:

NSString.contains(_:) in Swift is really the Objective-C method -[NSString containsString:]. The documentation for this method says:

Calling this method is equivalent to calling rangeOfString:options: with no options.

The documentation for rangeOfString:options: says:

NSString objects are compared by checking the Unicode canonical equivalence of their code point sequences.

So this method presumably treats combining sequences as single units by default. Here's a little Obj-C snippet to confirm the behavior you've seen from Swift:

NSString *s = @"A\u0300";
NSRange range = [s rangeOfString:@"A" options:0];
// returns { location: NSNotFound, length: 0 }, aka "not found"

This should be good news from the perspective of Swift because it means that NSString.contains(_:)'s behavior is closer to what you'd expect from String in many cases.