http://dev.clojure.org/jira This file is an XML representation of an issue en-us 4.4 649 25-07-2011 http://dev.clojure.org/jira/browse/CLJ-1128 Clojure <p>Set a first map as an initial value for reduce to<br/> avoid merge-entry (series of contains? calls and etc) call on the first map.</p> CLJ-1128

Improve merge-with

Enhancement Minor Open Unresolved Unassigned Edward Tsech Thu, 13 Dec 2012 13:29:35 -0600 Thu, 13 Dec 2012 17:41:39 -0600 0 2 <p>Tests pass.</p> <p>Edward, your patch replaces the expression (or m1 {}) with m1. It was changed from m1 to (or m1 {}) in a commit on Oct 16, 2008 with descriptive text "improved nil handling in merge, merge-with", so I am pretty sure it would be best to leave it as (or m1 {}). I believe the intent is to allow all but one of the map arguments to merge-with be nil, and everything will still work.</p> <p>The rest of the patch for avoiding one merge call seems sound to me.</p> <p>Your change would be even better at preserving any metadata on the first non-nil map in the list, if instead of calling with the first map, it called it with the first non-nil item of the list, and then the rest of the list after that.</p> <p>I figured out that `reduce1` did pass a head of the list for me. <img class="emoticon" src="http://dev.clojure.org/jira/images/icons/emoticons/smile.gif" height="20" width="20" align="absmiddle" alt="" border="0"/> (<a href="https://github.com/clojure/clojure/blob/master/src/clj/clojure/core.clj#L887">https://github.com/clojure/clojure/blob/master/src/clj/clojure/core.clj#L887</a>)<br/> But case with first nil argument is still valid. Correct me, please, if i'm wrong.</p> <p>I'm not sure about `(or m1 {})`. I don't see any problems which can happen. Probably behaviour of functions which are used internally was changed since 2008.</p> <p>(contains? nil :a) ;=&gt; false<br/> (assoc nil :a 1) ;=&gt; {:a 1}<br/> (get nil :a) ;=&gt; nil</p> <p>I could write some tests for that.</p> Global Rank Patch Code