{"id":42045,"date":"2024-02-06T13:26:43","date_gmt":"2024-02-06T18:26:43","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=42045"},"modified":"2024-02-06T13:26:43","modified_gmt":"2024-02-06T18:26:43","slug":"swift-tricks","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2024\/02\/06\/swift-tricks\/","title":{"rendered":"Swift Tricks"},"content":{"rendered":"

André Jorgensen<\/a>:<\/p>\n

Generic typealias can be used to simplify param types etc<\/p>

typealias Parser<A> = (String) -> [(A, String)]<\/pre>\n
[…]<\/p>\n
func parse<A>(stringToParse: String, parser: Parser)<\/pre>\n
[…]<\/p>\n
Finding Elements of Specific Type in Swift<\/p>\n
\nextension Array {\n    func whereType<T>() -> [T] {\n        compactMap { $0 as? T } \/\/ The function \"compactMap(\" in Swift is incredibly useful. It maps each element of an array to another optional type and returns the value if it exists (is not null).\n    }\n}<\/pre>\n<\/blockquote>\n
I’ve been using a version of this where the type is passed as a parameter. With this version it’s determined using type inference from the call site.<\/p>\n
He currently has 202 other tricks listed.<\/p>\n\n
Wade Tregaskis<\/a>:<\/p>\n
\n
for case let rep as NSBitmapImageRep in image.representations {\n    … \/\/ `rep` is an NSBitmapImageRep.  Non-bitmap reps are skipped.\n}<\/pre>\n
I sometimes forget that this is possible (and even more often exactly what the damn syntax is – kudos to vacawama<\/a> in today’s case of this for reminding me with their StackOverflow answer<\/a>).  There are numerous other ways to write the above, but I think it is the most elegant.<\/p>\n<\/blockquote>\n
I’ve been writing Swift for almost 10 years and still have to think to remember this syntax, as well as if case let<\/code>. I know<\/em> that case<\/code> is for pattern matching, but it still looks weird to see it there, and this is the same reason it’s written using as<\/code> without the question mark that normally accompanies downcasts that might fail. You might expect to be able to write:<\/p>\n
for rep as? NSBitmapImageRep in image.representations {<\/pre>\n
but instead Swift gives us case let<\/code> and a more general pattern matching feature. If you write this or get it correct except for the ?<\/code>, the compiler’s error messages are unhelpful:<\/p>\n\n
for rep as? NSBitmapImageRep in image.representations {\n\/\/ Expected 'in' after for-each pattern\n\nfor case let rep as? NSBitmapImageRep in image.representations {\n\/\/ Pattern variable binding cannot appear in an expression\n<\/pre>\n\n
Previously:<\/p>\n