{"action":"created","comment":{"url":"https://api.github.com/repos/apache/spark/pulls/comments/31199699","id":31199699,"diff_hunk":"@@ -125,7 +133,9 @@ case class GroupExpression(children: Seq[Expression]) extends Expression {\n  * so that the proper type conversions can be performed in the analyzer.\n  */\n trait ExpectsInputTypes {\n+  self: Expression =>\n \n   def expectedChildTypes: Seq[DataType]\n \n+  override def validInputTypes: Boolean = children.map(_.dataType) == expectedChildTypes","path":"sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/Expression.scala","position":37,"original_position":37,"commit_id":"029c5b6eb8f925e4058d3c9609452767ebf17af2","original_commit_id":"029c5b6eb8f925e4058d3c9609452767ebf17af2","user":{"login":"rxin","id":323388,"avatar_url":"https://avatars.githubusercontent.com/u/323388?v=3","gravatar_id":"","url":"https://api.github.com/users/rxin","html_url":"https://github.com/rxin","followers_url":"https://api.github.com/users/rxin/followers","following_url":"https://api.github.com/users/rxin/following{/other_user}","gists_url":"https://api.github.com/users/rxin/gists{/gist_id}","starred_url":"https://api.github.com/users/rxin/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/rxin/subscriptions","organizations_url":"https://api.github.com/users/rxin/orgs","repos_url":"https://api.github.com/users/rxin/repos","events_url":"https://api.github.com/users/rxin/events{/privacy}","received_events_url":"https://api.github.com/users/rxin/received_events","type":"User","site_admin":false},"body":"That should be fine right? \r\n\r\nAlso - add inline comment explaining this (i.e. things get casted).\r\n","created_at":"2015-05-28T02:49:44Z","updated_at":"2015-05-28T02:49:44Z","html_url":"https://github.com/apache/spark/pull/6405#discussion_r31199699","pull_request_url":"https://api.github.com/repos/apache/spark/pulls/6405","_links":{"self":{"href":"https://api.github.com/repos/apache/spark/pulls/comments/31199699"},"html":{"href":"https://github.com/apache/spark/pull/6405#discussion_r31199699"},"pull_request":{"href":"https://api.github.com/repos/apache/spark/pulls/6405"}}},"pull_request":{"url":"https://api.github.com/repos/apache/spark/pulls/6405","id":36178481,"html_url":"https://github.com/apache/spark/pull/6405","diff_url":"https://github.com/apache/spark/pull/6405.diff","patch_url":"https://github.com/apache/spark/pull/6405.patch","issue_url":"https://api.github.com/repos/apache/spark/issues/6405","number":6405,"state":"open","locked":false,"title":"[WIP][SPARK-7562][SPARK-6444][SQL] Improve error reporting for expression data type mismatch","user":{"login":"cloud-fan","id":3182036,"avatar_url":"https://avatars.githubusercontent.com/u/3182036?v=3","gravatar_id":"","url":"https://api.github.com/users/cloud-fan","html_url":"https://github.com/cloud-fan","followers_url":"https://api.github.com/users/cloud-fan/followers","following_url":"https://api.github.com/users/cloud-fan/following{/other_user}","gists_url":"https://api.github.com/users/cloud-fan/gists{/gist_id}","starred_url":"https://api.github.com/users/cloud-fan/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/cloud-fan/subscriptions","organizations_url":"https://api.github.com/users/cloud-fan/orgs","repos_url":"https://api.github.com/users/cloud-fan/repos","events_url":"https://api.github.com/users/cloud-fan/events{/privacy}","received_events_url":"https://api.github.com/users/cloud-fan/received_events","type":"User","site_admin":false},"body":"It seems hard to find a common pattern of checking types in `Expression`. Sometimes we know what input types we need(like `And`, we know we need two booleans), sometimes we just have some rules(like `Add`, we need 2 numeric types which are equal). So I defined a very general interface `TypeConstraint` with two sub-interfaces `ExpectsInputTypes` and `TypeEqualConstraint`. I'm still seeking a better generalization.\r\n\r\nThis PR mainly works on apply input types checking for arithmetic and predicate expressions.\r\n\r\nI also abstracted some common patterns to reduce code size:\r\n* abstract the usage of getting a `Numeric[Any]` or `Ordering[Any]`\r\n* abstract the type check for numeric, bitwise, ordering, etc.\r\n\r\nTODO:\r\n* When detect data types mismatch, we may need to do type casting(`ExpectsInputTypes` defines the casting behavior). Should we generalize it?\r\n* docs and 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