javascript - AngularJS : Passing a function to an isolated scope of a directive to be called within its controller? -

i'm trying call function passed controller's scope directive via "&" operation directive's controller. method, however, claimed angular undefined. after reading code on , over, scouring internet, , repeating process, i've decided turn here.

here's relevant part of controller. contains method pass directive.

angular.module('myapp.controllers', []).controller('postctrl', ['$scope', 'postalservice', function($scope, postalservice) {     $scope.posts = [];      $scope.getposts = function() {         postalservice.getposts(function(err, posts) {             if(err);             else $scope.posts = posts;         });     }; }]); 

here's directive. unable invoke onpost.

angular.module('myapp.directives', []).directive('compose', ['postalservice', function(postalservice) {     return {         restrict: 'e',         transclude: false,         replace: true,         scope: {             onpost: "&" //why not         },         templateurl: "partials/components/compose-partial.html",         controller: function($scope, postalservice) {             $scope.title = "";             $scope.content = "";             $scope.newpost = function() {                 postalservice.newpost($scope.title, $scope.content, function(err) {                     if(err) console.log(err + ":(");                     else {                         console.log("success getting posts.");                         //why can not invoke onpost()??                         $scope.onpost();                     }                 });             };         },     }; }]); 

and here's relevant part of html

<div ng-controller="postctrl">     <section class="side-bar panel hide-for-small">         <compose onpost="getposts()"></compose>     </section>      <!--more, non-relevant html here-->  </div> 

i know problem not postalservice service. instead, directive reports no function passed it. why??

replace

<compose onpost="getposts()"></compose> 

with

<compose on-post="getposts()"></compose> 

and it'll work.

the angular docs why it's so:

directives have camel cased names such ngbind. directive can invoked translating camel case name snake case these special characters :, -, or _.