I’ve been doing a lot of work with templates lately, for my R* tree implementation (which is morphing into a R* tree and a B tree library) and some things that I’ve been playing around with for Roadnav, especially in regards to serialization.<\/p>\n
Heres a neat snippet that I created:<\/p>\n
template <bool>\r\nstruct delete_if {\r\n\ttemplate <typename T>\r\n\tstatic void del(T t) { delete t; }\r\n};\r\n\r\ntemplate <>\r\nstruct delete_if\r\n{\r\n\ttemplate <typename T>\r\n\tstatic void del(T t) { \/* no-op, doesn't delete *\/ }\r\n};<\/pre>\nThis uses a partial specialization to do the decision portion, and a static member template to eliminate some of the typing (you could get rid of the member template, and you would end up calling delete_if<type, delete_item>::del ).<\/p>\n
So what this is intended for is those cases where you are implementing some generic container, and you don’t know whether the type you have is a pointer or not. You *could* use a normal bool as a parameter:<\/p>\n
if (delete_it) delete var;<\/pre>\nBut primary problem with this is that it won’t compile if the type isn’t a pointer. So a sample of something similar to what I’m using it for is something like this:<\/p>\n
template < typename T, bool delete_item >\r\nclass test {\r\npublic:\r\n\r\n\t~test()\r\n\t{\r\n\t\t\/\/ only release the item if the client specifies\r\n\t\t\/\/ that they want to\r\n\t\tdelete_if<delete_item>::del(val);\r\n\t}\r\n\r\nprivate:\r\n\tT val;\r\n};<\/pre>\nObviously this is just a really simple example of how you can use this. One could also use boost::is_pointer to detect whether the type is a pointer, and pass *that* to delete_if while using a ‘normal’ variable to determine whether the client wants to have the item be deleted or not. I leave that as an exercise for the reader.<\/p>\n","protected":false},"excerpt":{"rendered":"
I’ve been doing a lot of work with templates lately, for my R* tree implementation (which is morphing into a R* tree and a B tree library) and some things that I’ve been playing around with for Roadnav, especially in regards to serialization. Heres a neat snippet that I created: template <bool> struct delete_if { […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[40,31],"tags":[],"_links":{"self":[{"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/194"}],"collection":[{"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=194"}],"version-history":[{"count":3,"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/194\/revisions"}],"predecessor-version":[{"id":196,"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/194\/revisions\/196"}],"wp:attachment":[{"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=194"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=194"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.virtualroadside.com\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=194"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}