{"id":11921,"date":"2015-08-03T10:01:18","date_gmt":"2015-08-03T14:01:18","guid":{"rendered":"http:\/\/mjtsai.com\/blog\/?p=11921"},"modified":"2015-08-05T09:47:12","modified_gmt":"2015-08-05T13:47:12","slug":"swift-protocols-arrays-and-casting","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2015\/08\/03\/swift-protocols-arrays-and-casting\/","title":{"rendered":"Swift Protocols, Arrays, and Casting"},"content":{"rendered":"

Brent Simmons<\/a> (tweet<\/a>):<\/p>\r\n

But an EmailMessage is<\/em> a NodeRepresentedObject, so it ought to work just fine.<\/p>\r\n

[…]<\/p>\r\n

The best way I’ve found to deal with this is to map it. […] That seems crazy. I’m using map to create an array whose members are absolutely identical to the original array.<\/p><\/blockquote>\r\n\r\n

Kevin<\/a> Ballard<\/a>:<\/p>\r\n

It’s not a type-check. The in-memory representation is different. It has to allocate a new array with the new values.<\/p><\/blockquote>\r\n

Non-@objc protocols use a virtual function table (called a protocol witness table) rather than message-passing.<\/p><\/blockquote>\r\n

This means that objects typed as EmailMessage have a different table pointer than those typed as NodeRepresentedObject.<\/p><\/blockquote>\r\n

Brent Simmons<\/a>:<\/p>\r\n

I’d argue that, instead, there shouldn’t be a hidden performance gotcha.<\/p><\/blockquote>\r\n

Kevin<\/a> Ballard<\/a>:<\/p>\r\n

That would be nice, but the only way to solve this without a new array basically requires all protocols to use message-passing<\/p><\/blockquote>\r\n

Message passing is a performance gotcha :P<\/p><\/blockquote>\r\n

Brent Simmons<\/a>:<\/p>\r\n

But barely. We can write fast apps in Objective-C.<\/p><\/blockquote>\r\n

Kevin Ballard<\/a>:<\/p>\r\n

Yeah, but you should be able to write faster ones in Swift.<\/p><\/blockquote>\r\n

Brent Simmons<\/a>:<\/p>\r\n

Except for when I have to make an exact copy of an array to satisfy the type system.<\/p><\/blockquote>","protected":false},"excerpt":{"rendered":"

Brent Simmons (tweet): But an EmailMessage is a NodeRepresentedObject, so it ought to work just fine. […] The best way I’ve found to deal with this is to map it. […] That seems crazy. I’m using map to create an array whose members are absolutely identical to the original array. Kevin Ballard: It’s not a […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"apple_news_api_created_at":"","apple_news_api_id":"","apple_news_api_modified_at":"","apple_news_api_revision":"","apple_news_api_share_url":"","apple_news_coverimage":0,"apple_news_coverimage_caption":"","apple_news_is_hidden":false,"apple_news_is_paid":false,"apple_news_is_preview":false,"apple_news_is_sponsored":false,"apple_news_maturity_rating":"","apple_news_metadata":"\"\"","apple_news_pullquote":"","apple_news_pullquote_position":"","apple_news_slug":"","apple_news_sections":"\"\"","apple_news_suppress_video_url":false,"apple_news_use_image_component":false,"footnotes":""},"categories":[4],"tags":[46,966,54,138,71,901,943],"class_list":["post-11921","post","type-post","status-publish","format-standard","hentry","category-programming-category","tag-languagedesign","tag-message-passing","tag-objective-c","tag-optimization","tag-programming","tag-swift-programming-language","tag-swift-runtime"],"apple_news_notices":[],"_links":{"self":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/11921","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/comments?post=11921"}],"version-history":[{"count":1,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/11921\/revisions"}],"predecessor-version":[{"id":11922,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/11921\/revisions\/11922"}],"wp:attachment":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/media?parent=11921"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/categories?post=11921"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/tags?post=11921"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}