parameter problem in coroutine functions

[ghost]

If I use coroutine, can the parameters of the function only be passed by value like the first function, and can they be passed by reference like the second function?

[an-tao]

The parameters can't be passed by reference when using coroutines.

[ghost]

If I call a custom coroutine function in the handler function, can the called function be a reference parameter transfer?

[VladlenPopolitov]

When you take decision about reference parameter transfer, you have to consider the time of life for every parameter. You have to remember, that coroutines are not usual functions, they are created (coroutine handle and local memory allocated), called, returned execution to caller (looks like they sleep), resume again and again, and destroyed where they call co_return (handle and allocated variables memory destroyed and released).

1. If you pass to custom coroutine reference to global variable, it will exists longer , then you custom coroutine, you can pass by reference. Anyway, this global variable can be deleted in other part of the program, you have to understand it.
2. the same with static variables, you can send by reference, but it is your responsibility to know, can it be deleted somewhere outside of the coroutine code.
3. if coroutine call your custom coroutine, it can pass own local variables and own parameters to custom coroutine by reference, if you can guarantee, that caller coroutine will leave longer , than you custom coroutine.
   You have understand, that passing parameters by value does not guarantee the correct work. For example, you can pass std::string_view by value, but it will refer the data, that already destroyed. The rule is - pass object itself or reference (pointer) to the object, that will live longer, than coroutine.
   If you still not read some book about coroutines, I would recommend the good article - the best what I saw till now: https://www.scs.stanford.edu/~dm/blog/c++-coroutines.html . It could take 2-3 days to make all examples and rethink the ideas.

[ghost]

Thank you very much!!