boost asio channels "no type named 'receive_cancelled_signature'"

Question

I'm trying to implement a thread safe observer design pattern using boost so I want to iterate over a list of boost asio channels?

Say I have

struct A{};

std::list<boost::asio::experimental::channel<void(std::error_code, std::shared_ptr<A>>> channels;

for (auto it = channels.begin(); it != channels.end(); ++it)
{}

Using this code I got :

error, no type named 'receive_cancelled_signature'.

When I remove the for loop, the program compiles without errors Is it possible to iterate over channels in boost asio ?

Answer 1

Simpler repro: Live On Coliru

#include <boost/asio/experimental/channel.hpp>
#include <boost/asio/system_executor.hpp>

using Channel = boost::asio::experimental::channel<void(std::error_code, size_t)>;

int main() {
    Channel c(boost::asio::system_executor{});
}

shared_ptr, A, list and the loop had nothing to do with it.

Your mistake is that you use std::error_code which isn't supported by default.

Standalone Asio does use std::error_code, and perhaps Boost Asio can be configured to do so.

Keep in mind that Boost System has more features, and excellent interop with std::error_code these days.

Fix

Use boost::system::error_code:

Live On Coliru

#include <boost/asio.hpp>
#include <boost/asio/experimental/channel.hpp>
#include <iostream>
#include <list>

using Channel = boost::asio::experimental::channel<void(boost::system::error_code, size_t)>;


int main() {
    boost::asio::io_context ctx;

    std::list<Channel> channels;

    for (auto n = 5; n--;)
        channels.emplace_back(ctx);

    for (Channel& ch : channels) {
        std::cout << "Ch at address " << &ch << std::endl;
    }
}

Prints e.g.

Ch at address 0x2047d90
Ch at address 0x2048130
Ch at address 0x2048470
Ch at address 0x20487b0
Ch at address 0x2048af0