I’ve got one type of collection and I want to apply a function to each member of the collection, thereby producing a new collection.<\/p>\n
Surely there’s a standard pattern for this?<\/p>\n
In JavaScript, it’s called In C#, it’s In C++, it’s, um, this clumsy It’s clumsy because you need to give a name to the thing being transformed, because you need to call both It’s clumsy because you have to construct an empty Would be nice if there were some helper function like<\/p>\n Maybe one exists and I’m missing it? Help me out here.<\/p>\n \u00b9 You can avoid extending the lifetime beyond the transform by pushing it into a lambda:<\/p>\n but that’s basically just taking the Or maybe you should expect to write it out the slow way.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-103498","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":" Or maybe you should expect to write it out the slow way.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/103498","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=103498"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/103498\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=103498"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=103498"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=103498"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}map<\/code>:<\/p>\nfunction getOldValues()\r\n{\r\n return [\"a\", \"b\", \"c\", \"d\"];\r\n}\r\n\r\nvar newValues = getOldValues().map(v => v.charCodeAt(0));\r\n\/\/ result: [97, 98, 99, 100]\r\n<\/pre>\nSelect<\/code>.<\/p>\nstring[] GetOldValues() => new[] { \"a\", \"b\", \"c\", \"d\" };\r\n\r\nvar newValues = GetOldValues().Select(v => (int)v[0]).ToArray();\r\n\/\/ result: int[] { 97, 98, 99, 100 };\r\n<\/pre>\nstd::transform<\/code>.<\/p>\nstd::vector<std::string> GetOldValues()\r\n{\r\n return { \"a\", \"b\", \"c\", \"d\" };\r\n}\r\n\r\nauto oldValues = GetOldValues();\r\nstd::vector<int> newValues;\r\nnewValues.reserve(oldValues.size());\r\nstd::transform(oldValues.begin(), oldValues.end(),\r\n std::back_inserter(newValues),\r\n [](auto&& v) { return v[0]; });\r\n<\/pre>\nbegin<\/code> and end<\/code> on it. But giving it a name extends its lifetime, so you end up carrying this oldValues<\/code> vector around for no reason.\u00b9<\/p>\nnewValues<\/code> and then fill it in.<\/p>\ntemplate<typename T, typename U, typename TLambda>\r\nT transform_to(U&& u, TLambda&& lambda)\r\n{\r\n T result;\r\n if constexpr (has_size_v<U> && has_reserve_v<T>)\r\n {\r\n result.reserve(u.size());\r\n }\r\n std::transform(u.begin(), u.end(), std::back_inserter(result),\r\n std::forward<TLambda>(lambda));\r\n return result;\r\n}\r\n\r\nauto newValues = std::transform_to<std::vector<int>>(\r\n GetOldValues(), [](auto&& v) { return v[0]; });\r\n<\/pre>\nauto newValues = [&]()\r\n{\r\n auto oldValues = GetOldValues();\r\n std::vector<int> newValues;\r\n newValues.reserve(oldValues.size());\r\n std::transform(oldValues.begin(), oldValues.end(),\r\n std::back_inserter(newValues),\r\n [](auto&& v) { return v[0]; });\r\n return newValues;\r\n}();\r\n<\/pre>\ntransform_to<\/code> function and inlining it as a lambda.<\/p>\n","protected":false},"excerpt":{"rendered":"