traits

问题 I'm writing very basic AI system in Rust. It's main components are: Action s, which can be implemented by library user, for specific use, Generic Context , which is passed to all actions, and only needs to live during the action execution, ActionsContainer , which "globally" stores all possible actions, System , which chooses the correct action and runs it. There are many systems, one for each agent. However, they share the same set of behaviours, so they all reference a common

问题 I have a Java / Scala mix Maven project. I need to reuse a Saddle method make that is concretely defined as part of a trait called Index . The method is defined here if that helps in any way. I have tried calling that method from java using Index.make or Index$class.make but in both cases I get the error: cannot find symbol compilation error. Is there a way to call a concrete Trait method from Java? 回答1: A trait is similar to a Java interface in a sense that it is not a concrete constructor.

问题 The code pub trait Q<S> { fn f(); } pub trait A { type I; type F: Q<Self::I>; } // this works (1) // // pub struct S<T> // where // T: A // { // unsatisfied trait bound (2) pub struct S<T> where T: A<I = bool>, { t: T, } fails to compile: error[E0277]: the trait bound `<T as A>::F: Q<bool>` is not satisfied --> src/main.rs:18:1 | 18 | / pub struct S<T> 19 | | where 20 | | T: A<I = bool>, 21 | | { 22 | | t: T, 23 | | } | |_^ the trait `Q<bool>` is not implemented for `<T as A>::F` | = help:

问题 I'm using CakePHP 2.4.5 and PHP 5.5, and would like to use a trait. I have a trait in Utility/VariablesTrait.php called VariablesTrait . To take advantage of namespaces, I've given it a namespace of App\Utility\VariablesTrait , since Utility\VariablesTrait seems a bit too global, and the former would work better with CakePHP 3. In my class that I want to use it in, I have the use App\Utility\VariablesTrait; statement in the class. For backup, I also have a App::uses('VariablesTrait', 'Utility

问题 In many blog about Groovy Traits it's mentioned that it will solve the Diamond Problem. But the concept is not clear to me that how traits will solve the Diamond Problem. Can any one explain please. 回答1: The diamond problem is a problem when you have multiple inheritance and two or more super classes define one or more functions with the same signature. With groovy traits, the behaviour is well-defined. By default, the last implementation is chosen. trait A { String name() { "A" } } trait B {

问题 I'm trying to understand how to implement a generic trait in Rust. While I've seen a number of examples, the examples are too tied to a specific use (e.g. genomic mutators) for me to be able to understand at this point in my Rust development. Instead, here's a simple example based on something fairly universal--incrementing: trait Incrementable { fn post_inc(&mut self) -> Self; fn post_inc_by(&mut self, n: usize) -> Self; } impl Incrementable for usize { fn post_inc(&mut self) -> Self { let

问题 When attempting to answer this question, I wrote this code: trait MyTrait { type A; type B; } trait WithFoo: MyTrait { fn foo(a: Self::A) -> Self::B; } impl<T, U: MyTrait<A = T, B = T>> WithFoo for U { fn foo(a: T) -> T { a } } struct S1; impl MyTrait for S1 { type A = u32; type B = f32; } impl WithFoo for S1 { fn foo<T>(a: Self::A) -> Self::B { a as f32 } } struct S2; impl MyTrait for S2 { type A = u32; type B = u32; } fn main() { S1::foo(42); S2::foo(42); } playground This fails to compile

问题 I have a class template with a member function that has a lambda which wants to use a class template parameter type. It fails to compile inside the lambda but succeeds, as anticipated, outside the lambda. struct wcout_reporter { static void report(const std::wstring& output) { std::wcout << output << std::endl; } }; template <typename reporter = wcout_reporter> class agency { public: void report_all() { reporter::report(L"dummy"); // Compiles. std::for_each(reports_.begin(), reports_.end(),

问题 I'm trying to define a function that will take a reference as a parameter, and call a generic method on the referenced object, passing in a concrete value. I need a way of requiring that the generic type of the parameter passed to my function is a trait of the concrete type that the function will use it with. I can't seem to work out how to do this. A minimal example of the sort of thing I'm trying to achieve: trait Vehicle {} trait Floating {} struct Boat; impl Vehicle for Boat {} impl

问题 Code: trait Trait<T> {} struct Struct<U>; impl<T, U: Trait<T>> Struct<U> {} Error: error[E0207]: the type parameter `T` is not constrained by the impl trait, self type, or predicates --> src/main.rs:5:6 | 5 | impl<T, U: Trait<T>> Struct<U> {} | ^ unconstrained type parameter It seems that RFC 447 prohibits this pattern; is there any way to work around this? I think it could be solved by changing T to an associated type, but that would prevent me from doing multidispatch. 回答1: A type parameter