{"action":"created","comment":{"url":"https://api.github.com/repos/elastic/elasticsearch/pulls/comments/88029487","pull_request_review_id":8615351,"id":88029487,"diff_hunk":"@@ -0,0 +1,125 @@\n+/*\n+ * Licensed to Elasticsearch under one or more contributor\n+ * license agreements. See the NOTICE file distributed with\n+ * this work for additional information regarding copyright\n+ * ownership. Elasticsearch licenses this file to you under\n+ * the Apache License, Version 2.0 (the \"License\"); you may\n+ * not use this file except in compliance with the License.\n+ * You may obtain a copy of the License at\n+ *\n+ *    http://www.apache.org/licenses/LICENSE-2.0\n+ *\n+ * Unless required by applicable law or agreed to in writing,\n+ * software distributed under the License is distributed on an\n+ * \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY\n+ * KIND, either express or implied.  See the License for the\n+ * specific language governing permissions and limitations\n+ * under the License.\n+ */\n+\n+package org.elasticsearch.painless.node;\n+\n+import org.elasticsearch.painless.AnalyzerCaster;\n+import org.elasticsearch.painless.Definition;\n+import org.elasticsearch.painless.Definition.Type;\n+import org.elasticsearch.painless.Globals;\n+import org.elasticsearch.painless.Locals;\n+import org.elasticsearch.painless.Location;\n+import org.elasticsearch.painless.MethodWriter;\n+import org.objectweb.asm.Label;\n+\n+import java.util.Set;\n+\n+import static java.util.Objects.requireNonNull;\n+\n+/**\n+ * The Elvis operator ({@code ?:}), a null coalescing operator. Binary operator that evaluates the first expression and return it if it is\n+ * non null. If the first expression is null then it evaluates the second expression and returns it.\n+ */\n+public class EElvis extends AExpression {","path":"modules/lang-painless/src/main/java/org/elasticsearch/painless/node/EElvis.java","position":39,"original_position":39,"commit_id":"f1a230eb92e15938f5a515b69113c10e92f80159","original_commit_id":"f1a230eb92e15938f5a515b69113c10e92f80159","user":{"login":"nik9000","id":215970,"avatar_url":"https://avatars.githubusercontent.com/u/215970?v=3","gravatar_id":"","url":"https://api.github.com/users/nik9000","html_url":"https://github.com/nik9000","followers_url":"https://api.github.com/users/nik9000/followers","following_url":"https://api.github.com/users/nik9000/following{/other_user}","gists_url":"https://api.github.com/users/nik9000/gists{/gist_id}","starred_url":"https://api.github.com/users/nik9000/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nik9000/subscriptions","organizations_url":"https://api.github.com/users/nik9000/orgs","repos_url":"https://api.github.com/users/nik9000/repos","events_url":"https://api.github.com/users/nik9000/events{/privacy}","received_events_url":"https://api.github.com/users/nik9000/received_events","type":"User","site_admin":false},"body":"I spent a while thinking about this and I think I like the way I have it better. The thing that worries me is that we'd need to introduce a synthetic variable to keep from from evaluating the lhs twice. We can do that but it seems a bit complex and heavy. By heavy I mean that it relies on the jit to eliminate it. I expect it mostly can but the bytecode that EElvis emits is more obviously efficient to me.\r\n\r\nOne thing I'd like to do as a followup to this is to investigate the extra box/unbox step you get in code like `int x = foo?.x :? 0` when `foo.x` has return type `int`. I think the no-node approach or the node approach can optimize this away, I think. I feel like the approach I've started with is going to be easier/more obvious about it. I'm not even sure it is needed though. I'd have to run some comparisons to check first. I don't think that is a good argument for the node approach because it might not be needed at all and it might not be simpler but I wanted to type it out because it has been rattling around in my head.","created_at":"2016-11-15T14:44:00Z","updated_at":"2016-11-15T14:44:00Z","html_url":"https://github.com/elastic/elasticsearch/pull/21506#discussion_r88029487","pull_request_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/21506","_links":{"self":{"href":"https://api.github.com/repos/elastic/elasticsearch/pulls/comments/88029487"},"html":{"href":"https://github.com/elastic/elasticsearch/pull/21506#discussion_r88029487"},"pull_request":{"href":"https://api.github.com/repos/elastic/elasticsearch/pulls/21506"}}},"pull_request":{"url":"https://api.github.com/repos/elastic/elasticsearch/pulls/21506","id":93379064,"html_url":"https://github.com/elastic/elasticsearch/pull/21506","diff_url":"https://github.com/elastic/elasticsearch/pull/21506.diff","patch_url":"https://github.com/elastic/elasticsearch/pull/21506.patch","issue_url":"https://api.github.com/repos/elastic/elasticsearch/issues/21506","number":21506,"state":"open","locked":false,"title":"Implement the ?: operator in painless","user":{"login":"nik9000","id":215970,"avatar_url":"https://avatars.githubusercontent.com/u/215970?v=3","gravatar_id":"","url":"https://api.github.com/users/nik9000","html_url":"https://github.com/nik9000","followers_url":"https://api.github.com/users/nik9000/followers","following_url":"https://api.github.com/users/nik9000/following{/other_user}","gists_url":"https://api.github.com/users/nik9000/gists{/gist_id}","starred_url":"https://api.github.com/users/nik9000/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nik9000/subscriptions","organizations_url":"https://api.github.com/users/nik9000/orgs","repos_url":"https://api.github.com/users/nik9000/repos","events_url":"https://api.github.com/users/nik9000/events{/privacy}","received_events_url":"https://api.github.com/users/nik9000/received_events","type":"User","site_admin":false},"body":"Implements a [null coalescing operator](https://en.wikipedia.org/wiki/Null_coalescing_operator) in painless that looks like `?:`. This form was chosen to emulate Groovy's `?:` operator. It is different in that it only coalesces `null` values, instead of Groovy's `?:` operator which coalesces all [falsy](http://groovy-lang.org/semantics.html#Groovy-Truth) values. I believe that makes it the same as Kotlin's `?:` operator. In other languages this operator looks like `??` (C#) and `COALESCE` ([SQL](https://www.postgresql.org/docs/9.1/static/functions-conditional.html#FUNCTIONS-COALESCE-NVL-IFNULL)) `:-` (bash).\r\n\r\nThis operator is lazy, meaning the right hand side is only evaluated at all if the left hand side is null.","created_at":"2016-11-11T18:50:22Z","updated_at":"2016-11-15T14:44:00Z","closed_at":null,"merged_at":null,"merge_commit_sha":"ff1c863c75845607bdb3746caba0178d0973d32d","assignee":null,"assignees":[],"milestone":null,"commits_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/21506/commits","review_comments_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/21506/comments","review_comment_url":"https://api.github.com/repos/elastic/elasticsearch/pulls/comments{/number}","comments_url":"https://api.github.com/repos/elastic/elasticsearch/issues/21506/comments","statuses_url":"https://api.github.com/repos/elastic/elasticsearch/statuses/f1a230eb92e15938f5a515b69113c10e92f80159","head":{"label":"nik9000:elvis","ref":"elvis","sha":"f1a230eb92e15938f5a515b69113c10e92f80159","user":{"login":"nik9000","id":215970,"avatar_url":"https://avatars.githubusercontent.com/u/215970?v=3","gravatar_id":"","url":"https://api.github.com/users/nik9000","html_url":"https://github.com/nik9000","followers_url":"https://api.github.com/users/nik9000/followers","following_url":"https://api.github.com/users/nik9000/following{/other_user}","gists_url":"https://api.github.com/users/nik9000/gists{/gist_id}","starred_url":"https://api.github.com/users/nik9000/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nik9000/subscriptions","organizations_url":"https://api.github.com/users/nik9000/orgs","repos_url":"https://api.github.com/users/nik9000/repos","events_url":"https://api.github.com/users/nik9000/events{/privacy}","received_events_url":"https://api.github.com/users/nik9000/received_events","type":"User","site_admin":false},"repo":{"id":11487195,"name":"elasticsearch","full_name":"nik9000/elasticsearch","owner":{"login":"nik9000","id":215970,"avatar_url":"https://avatars.githubusercontent.com/u/215970?v=3","gravatar_id":"","url":"https://api.github.com/users/nik9000","html_url":"https://github.com/nik9000","followers_url":"https://api.github.com/users/nik9000/followers","following_url":"https://api.github.com/users/nik9000/following{/other_user}","gists_url":"https://api.github.com/users/nik9000/gists{/gist_id}","starred_url":"https://api.github.com/users/nik9000/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/nik9000/subscriptions","organizations_url":"https://api.github.com/users/nik9000/orgs","repos_url":"https://api.github.com/users/nik9000/repos","events_url":"https://api.github.com/users/nik9000/events{/privacy}","received_events_url":"https://api.github.com/users/nik9000/received_events","type":"User","site_admin":false},"private":false,"html_url":"https://github.com/nik9000/elasticsearch","description":"Open 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