traits

问题 How can I deduce statically if an argument is a C++ function object (functor)? template <typename F> void test(F f) {} I tried is_function<F>::value , but this doesn't work. It also seems there is no is_functor trait, so perhaps it's not possible. I appear to be only looking for a specific member function, in this case the function call operator: F::operator() . 回答1: It is possible to create such a trait, with two restrictions: For the compiler, a free function is something fundamentally

问题 There is this code: // Initial object algebra interface for expressions: integers and addition trait ExpAlg[E] { def lit(x : Int) : E def add(e1 : E, e2 : E) : E } // An object algebra implementing that interface (evaluation) // The evaluation interface trait Eval { def eval() : Int } // The object algebra trait EvalExpAlg extends ExpAlg[Eval] { def lit(x : Int) = new Eval() { def eval() = x } def add(e1 : Eval, e2 : Eval) = new Eval() { def eval() = e1.eval() + e2.eval() } } I really would

问题 I'm learning Rust and I'm having difficulties in implementing polymorphism. I want to use an array to store either Circle or Test . trait Poli { fn area(&self) -> f64; } struct Circle { x: f64, y: f64, radius: f64, } impl Circle { fn new (xx: f64, yy: f64, r: f64) -> Circle{ Circle{ x: xx, y: yy, radius: r } } } impl Poli for Circle { fn area(&self) -> f64 { std::f64::consts::PI * (self.radius * self.radius) } } struct Test { x: f64, y: f64, radius: f64, test: f64, } impl Test { fn new (xx:

问题 I posted a similar question (Rust lifetime error expected concrete lifetime but found bound lifetime) last night, but still can't figure out how to apply it to this case now. Once again, a simplified example bellow: struct Ref; struct Container<'a> { r : &'a Ref } struct ContainerB<'a> { c : Container<'a> } trait ToC { fn from_c<'a>(r : &'a Ref, c : Container<'a>) -> Self; } impl<'b> ToC for ContainerB<'b> { fn from_c<'a>(r : &'a Ref, c : Container<'a>) -> ContainerB<'a> { ContainerB{c:c} } }

问题 In the project I work for, we often need to convert text to the value of a trait. Generally, we use the is_trait_type method to do the appropriate conversion. However, it doesn't work with Date traits. Here is a MWE: from traits.has_traits import HasTraits from traits.trait_types import Int, Date class A(HasTraits): a_date = Date an_int = Int a = A() class_traits = a.class_traits() print class_traits["an_int"].is_trait_type(Int) print class_traits["a_date"].is_trait_type(Date) The Int behave

问题 I was trying to create a simple trait to intercept received messages from arbitrary actors, using the stackable trait pattern. But when creating the Props , it turns out that Props(new A with B) is different from Props[A with B] . Namely, the first variant works but not the second one. Where is the difference? A minimal example: https://gist.github.com/ale64bit/df496ec2a43d0ec2ddb3 Thanks! 回答1: I'm not sure of the exact reason behind the behavior, but it would appear that using the

问题 Is there a way to reference items in a dictionary in traitsui views? In other words, is there a way to do what I mean with the following, using a Dict trait: from traits.api import * from traitsui.api import * from traitsui.ui_editors.array_view_editor import ArrayViewEditor import numpy as np class SmallPartOfLargeApplication(HasTraits): a=Dict def _a_default(self): return {'a_stat':np.random.random((10,1)), 'b_stat':np.random.random((10,10))} traits_view=View( Item('a.a_stat',editor

问题 Traits are much more efficient than behaviors as behaviors are objects that take both time and memory.so can anyone explain how i can write trait in yii2 ? 回答1: In General: A Trait is similar to a class, but only intended to group functionality in a fine-grained and consistent way. It is not possible to instantiate a Trait on its own. <?php trait Hello { public function sayHello() { echo 'Hello '; } } trait World { public function sayWorld() { echo 'World'; } } class MyHelloWorld { use Hello,

问题 I have a trait: trait AbstractSender { abstract SentTrigger sendMail(Mail main) SentTrigger sentTrigger(Mail mail){ //do smth here } } And I have a class: class EmailSender implements AbstractSender{ @Override SentTrigger sendMail(Mail mail){ //do some stuff } } I try to compile it using gmavenplus plugin: <plugin> <groupId>org.codehaus.gmavenplus</groupId> <artifactId>gmavenplus-plugin</artifactId> <version>1.5</version> <executions> <execution> <goals> <goal>addSources</goal> <goal

问题 This question already has answers here : Using .into() when type inference is impossible (4 answers) How to use std::convert::Into in statements in Rust? [duplicate] (1 answer) Closed 3 months ago . I'm trying to understand how the From trait works. I've seen it used a lot when you want to override an error from a library with your own custom error. I tried to come up with a contrived example to see that property in action: struct Blah{ } impl From<i32> for Blah { fn from(b:i32) -> Blah {