[英]C++ lambda as std::function in template function
Let's say we have this simplified version of my code:假设我们有我的代码的这个简化版本:
template<typename R>
R Context::executeTransient(std::function<R(VkCommandBuffer)> const &commands) {
...
R result = commands(commandBuffer);
...
return result;
}
I tried to pass a lambda function as a parameter to the function Context::executeTransient()
but it works only if I explicitly assign the lambda to a specific std::function
type. I tried to pass a lambda function as a parameter to the function Context::executeTransient()
but it works only if I explicitly assign the lambda to a specific std::function
type. This works:这有效:
std::function<int(VkCommandBuffer)> f = [](VkCommandBuffer commandBuffer) {
printf("Test execution");
return 1;
};
context.executeTransient(f);
The example above works but I'd like to achieve the example below because of aesthetic reasons and don't know if this is even possible:上面的例子有效,但由于美学原因,我想实现下面的例子,不知道这是否可能:
context.executeTransient([](VkCommandBuffer commandBuffer) {
printf("Test execution");
return 1;
});
My only requirement is that Context::executeTransient()
should accept lambdas and functions with a templated return type and input argument with some specific type eg VkCommandBuffer
.我唯一的要求是Context::executeTransient()
应该接受具有模板化返回类型的 lambda 和函数以及具有某些特定类型的输入参数,例如VkCommandBuffer
。
What about simply as follows?简单如下呢?
template <typename F>
auto Context::executeTransient (F const & commands) {
...
auto result = commands(commandBuffer);
...
return result;
}
This way your method accept both standard functions and lambdas (without converting them to standard functions, that is preferable, from the performance point of view (as far as I know)) and the return type is deduced from the use ( auto
).这样,您的方法同时接受标准函数和 lambdas(不将它们转换为标准函数,从性能的角度来看(据我所知)这是更可取的),并且返回类型是从使用( auto
)推导出来的。
In you need to know the R
type inside the method, you can apply decltype()
to result
在您需要知道方法内的R
类型时,您可以应用decltype()
到result
auto result = commands(commandBuffer);
using R = decltype(result);
If you need to know the R
type as template parameter of the method, its a little more complex because involve std::declval()
and, unfortunately, add redundancy如果您需要知道R
类型作为方法的模板参数,它有点复杂,因为涉及std::declval()
并且不幸的是,添加了冗余
template <typename F,
typename R = decltype(std::declval<F const &>()(commandBuffer))>
R Context::executeTransient (F const & commands) {
...
R result = commands(commandBuffer);
...
return result;
}
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