std :: async可以调用std :: function对象吗? [英] Can std::async call std::function objects?
问题描述
是否可以使用std :: async调用使用std :: bind创建的函数对象。以下代码无法编译:
Is it possible to call function objects created with std::bind using std::async. The following code fails to compile:
#include <iostream>
#include <future>
#include <functional>
using namespace std;
class Adder {
public:
int add(int x, int y) {
return x + y;
}
};
int main(int argc, const char * argv[])
{
Adder a;
function<int(int, int)> sumFunc = bind(&Adder::add, &a, 1, 2);
auto future = async(launch::async, sumFunc); // ERROR HERE
cout << future.get();
return 0;
}
错误是:
没有用于调用异步的匹配函数:
候选模板被忽略:替换失败[with Fp = std :: _1 :: function& ;, Args =< ;>]:'std :: _1 :: __ invoke_of中没有名为'type'的类型,>
No matching function for call to 'async': Candidate template ignored: substitution failure [with Fp = std::_1::function &, Args = <>]: no type named 'type' in 'std::_1::__invoke_of, >
是否不可能在std中使用异步:: function对象还是我做错了什么?
Is it just not possible to use async with std::function objects or am I doing something wrong?
(正在使用Xcode 5和Apple LLVM 5.0编译器进行编译)
(This is being compiled using Xcode 5 with the Apple LLVM 5.0 compiler)
推荐答案
是否可以使用以下方法调用使用
std :: bind
创建的函数对象std :: async
是的,您可以调用任何仿函数,只要
Yes, you can call any functor, as long as you provide the right number of arguments.
我做错了吗?
am I doing something wrong?
您正在将不带参数的绑定函数转换为 function< int(int,int)>
,它接受(并忽略)两个参数;
You're converting the bound function, which takes no arguments, to a function<int(int,int)>
, which takes (and ignores) two arguments; then trying to launch that with no arguments.
您可以指定正确的签名:
You could specify the correct signature:
function<int()> sumFunc = bind(&Adder::add, &a, 1, 2);
或避免创建函数的开销
:
auto sumFunc = bind(&Adder::add, &a, 1, 2);
或根本不用 bind
打扰:
auto future = async(launch::async, &Adder::add, &a, 1, 2);
或使用lambda:
auto future = async(launch::async, []{return a.add(1,2);});
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