std :: variant转换移动构造函数的模板专业化变量

时间：2018-07-19 18:23:19

标签： c++ constructor move variant

我正在使用一个封装std :: variant模板专业化的类，例如：

    org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'bindingService' defined in class path resource [org/springframework/cloud/stream/config/BindingServiceConfiguration.class]: Unsatisfied dependency expressed through method 'bindingService' parameter 1; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.cloud.stream.config.BinderFactoryConfiguration': Unsatisfied dependency expressed through field 'binderFactoryListeners'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.cloud.stream.config.BindersHealthIndicatorAutoConfiguration': Unexpected exception during bean creation; nested exception is java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:732) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:474) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1256) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1105) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:760) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550) ~[spring-context-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:759) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:395) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1255) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1243) [spring-boot-2.0.3.RELEASE.jar:2.0.3.RELEASE]
    at com.abc.uf.service.myApplicationServiceApplication.main(myApplicationServiceApplication.java:18) [classes/:na]
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.cloud.stream.config.BinderFactoryConfiguration': Unsatisfied dependency expressed through field 'binderFactoryListeners'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.cloud.stream.config.BindersHealthIndicatorAutoConfiguration': Unexpected exception during bean creation; nested exception is java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:587) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:91) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:373) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1350) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:372) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1256) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1105) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1138) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:818) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:724) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 19 common frames omitted
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.cloud.stream.config.BindersHealthIndicatorAutoConfiguration': Unexpected exception during bean creation; nested exception is java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:372) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1256) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1105) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:251) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.addCandidateEntry(DefaultListableBeanFactory.java:1325) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1291) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveMultipleBeans(DefaultListableBeanFactory.java:1193) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1096) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:584) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 42 common frames omitted
Caused by: java.lang.ArrayStoreException: sun.reflect.annotation.TypeNotPresentExceptionProxy
    at sun.reflect.annotation.AnnotationParser.parseClassArray(AnnotationParser.java:724) ~[na:1.8.0_152]
    at sun.reflect.annotation.AnnotationParser.parseArray(AnnotationParser.java:531) ~[na:1.8.0_152]
    at sun.reflect.annotation.AnnotationParser.parseMemberValue(AnnotationParser.java:355) ~[na:1.8.0_152]
    at sun.reflect.annotation.AnnotationParser.parseAnnotation2(AnnotationParser.java:286) ~[na:1.8.0_152]
    at sun.reflect.annotation.AnnotationParser.parseAnnotations2(AnnotationParser.java:120) ~[na:1.8.0_152]
    at sun.reflect.annotation.AnnotationParser.parseAnnotations(AnnotationParser.java:72) ~[na:1.8.0_152]
    at java.lang.Class.createAnnotationData(Class.java:3521) ~[na:1.8.0_152]
    at java.lang.Class.annotationData(Class.java:3510) ~[na:1.8.0_152]
    at java.lang.Class.createAnnotationData(Class.java:3526) ~[na:1.8.0_152]
    at java.lang.Class.annotationData(Class.java:3510) ~[na:1.8.0_152
    at java.lang.Class.getDeclaredAnnotation(Class.java:3458) ~[na:1.8.0_152]
    at org.springframework.core.KotlinDetector.isKotlinType(KotlinDetector.java:62) ~[spring-core-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.BeanUtils.findPrimaryConstructor(BeanUtils.java:199) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.determineCandidateConstructors(AutowiredAnnotationBeanPostProcessor.java:286) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineConstructorsFromBeanPostProcessors(AbstractAutowireCapableBeanFactory.java:1204) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1129) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503) ~[spring-beans-5.0.7.RELEASE.jar:5.0.7.RELEASE]
    ... 62 common frames omitted

我正在尝试使用转换的move构造函数从template<typename Type> struct Generic_node {...}; struct Leaf_node : Generic_node<...> {...}; struct Inner_node : Generic_node<...> {...}; struct Node {std::variant<Leaf_node, Inner_node> variant_;}; 中的函数构造一个Node，但是编译失败。

我定义了一个模板构造函数，该模板构造函数接受一个右值引用（假设是一个专门的类），并通过将值移动到变量中来构造变量，我希望在其中调用转换移动构造函数# (4)。 / p>

当我尝试创建最小的非工作示例时，我发现问题实际上仅从模板函数显示，如果我知道确切的类型（编译器知道的Generic_node），则移动构造会成功。因此，我认为总会发生一些意料之外的模板魔术。

Leaf_node == Generic_node<...>

相关的编译器错误消息（clang 7，libstdc ++-8）：

#include <variant>

template<typename T>
struct Base
{
    void f();
};

struct Derived : Base<int> {};

struct Variant
{
    // In real program expecting the T to be one of the multiple variants
    // Here I use only one variant because it suffices to illustrate the problem
    template<typename T>
    Variant(T&& t)
        :
        variant_ {std::move(t)}
    {
    }

    std::variant<Derived> variant_;
};

template<typename T>
void
Base<T>::
f()
{
    Variant {std::move(Derived {})}; // can call on  exact type
    Variant {std::move(Base<T> {})}; // can not call on specialized template type
}

int
main()
{
    Derived {}.f();
}

问题很可能与变量无关，而是与Variant构造函数的模板实例化中的note: candidate template ignored: substitution failure [with _Tp = Base<int>, $1 = void, $2 = void]: implicit instantiation of undefined template 'std::variant<Derived>::__to_type_impl<18446744073709551615, false>' variant(_Tp&& __t) 相等，编译器似乎没有看到。

模板实例化中发生了什么，为什么编译器不能调用提供的构造函数？

编辑：由于我打算创建专门化类，因此我忘记了继承不能暗示类类型相等，即使从技术上讲在这种特殊情况下也是如此。因此，这是一个容易的任务，即从特殊的Base构造“通过移动导出”：

Base<T> == Derived

如果我是对的，则需要为Base的每个派生类显式定义构造函数。

1 个答案:

答案 0 :(得分：0)

在您给出的示例中，Derived类是与Base不同的类。它们具有完全相同的成员，相同的方法，但是它们仍然是单独的类。

解决此问题的最简单方法是使用using语句，而不是将其声明为单独的类：

using Derived = Base<int>;
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