traits

What does Box<Fn() + Send + 'static> mean in rust? I stumbled upon this syntax while reading advanced types chapter. Send is a trait but what does it mean to + a lifetime to a trait ( 'static in this case) in type parametrization ? Also what is Fn() ? Masaki Hara Let's decompose it one-by-one. Box Box<T> is a pointer to heap-allocated T . We use it here because trait objects can only exist behind pointers. Trait objects In Box<Fn() + Send + 'static> , Fn() + Send + 'static is a trait object type. In future, it will be written Box<dyn (Fn() + Send + 'static)> to avoid confusion. Inside dyn are

I want to exclude all inherited methods from trait(s) from the list that are not overriden in a class So how to know if a class member is inherited from trait? Yes, I can check it like this: if ($trait->hasMethod($methodName) || $ref->getTraitAliases()[$methodName] !== null) { // } But what if the trait method is overriden in a class? How to know it? One way is to check if method bodies are similar, if so, i may exclude it, but is there a better way to achieve this? Important notes This is only because of "academical" interest, in real situation you should not care about - from where method

I'm wondering if there is any good reason why this behaviour is possible in the current PHP 5.4 implementation: trait T { public function test(PDO $pdo) {} } class C { use T; public function test(DOMDocument $dom) {} } I thought that the fact that a class uses a trait, guaranteed that this class had a specific interface available. But here, if we inadvertently override the trait method for another purpose, we don't even receive a Strict Standards notice, as with classic inheritance. Is this specifically allowed on purpose? What for? This behavior is documented. From php.net ( http://php.net

Could someone please help me understand Scala's various "Like" traits in the collection API. I've been reading over and trying to compare each without luck. I think I can see that Map for example, extends MapLike - adding 2 concrete methods. But this begs the question of why do this at all? Why not just have 1 Map trait in the Collections API instead of Map and MapLike? Thank you! The best source for these details is Martin Odersky and Lex Spoon's "What's New in Scala 2.8: The Architecture of Scala Collections" : The Scala collection library avoids code duplication and achieves the "same

I am new to C++ so please bear with me. I am trying to understand STL iterator_traits. In the book "The C++ Standard Library" the structure iterator_traits is defined as follows: template <class T> struct iterator_traits{ typedef typename T::value_type value_type typedef typename T::difference_type difference_type typedef typename T::iterator_category iterator_category typedef typename T::pointer pointer typedef typename T::reference reference } So it seems to me that it is re-exposing the subtypes that T already exposes. Moving ahead further, the book gives an example of how to use it, which

Is there any function in PHP (5.4) to get used traits as array or similar: class myClass extends movingThings { use bikes, tanks; __construct() { echo 'I\'m using the two traits:' . ????; // bikes, tanks } } To easily get the used traits you can call class_uses() $usedTraits = class_uses(MyClass); // or $usedTraits = class_uses($myObject); General recommendations When checking for available functionality, I would generally recommend to use interfaces . To add default functionality to an interface you would use traits . This way you can also benefit from type hinting. Force an object having