Before this commit, recursive coroutines did not work properly if they
had out arguments with reference type.
The reason is that `rc_run` was inferring the type of its arguments from
the arguments themselves, not from the prototype of the recursive
coroutine.
Hence, code snippets like the following did not work properly, because
`rc_run` was taking x by value, not by reference.
```
RecursiveCoroutine<void> accumulate_on_i(int &i) {
// ...
}
int f() {
int x = 0;
rc_run(accumulate_on_i, x);
return x;
}
```
This commit fixes the problem. Now the arguments of `rc_run` are
properly forwarded to the recursive coroutine.
RecursiveCoroutines are a facility intended to be used as-drop in
replacement of recursive functions.
They provide the following features.
- They can be written almost as regular recursive functions,
with 4 caveats.
1. A recursive coroutine that returns a type `T`, needs to be declared
to return a `RecursiveCoroutine<T>`.
2. Inside the body of a recursive coroutine, when recursively calling
another recursive coroutine, the recursive call needs to be
prepended by the new keyword `rc_recur`.
3. Inside the body of a recursive coroutine, the `return` statement
needs to be substituted with `rc_return`.
4. When launching a recursive coroutine `A` from a function that is
not a recursive coroutine, `A` needs to be called with the provided
dedicated template wrapper `rc_run`.
The syntax is the following `rc_run(A, arg0, arg1, ...)`.
This is necessary to enable swapping off recursive coroutine and
fall back to regular recursion for debug.
See below for how to do it.
- Unlike regular recursive functions, they don't use the system stack
for recursion. They use a custom heap-allocated stack to manage
recursion. This makes them more robust for implementing recursive
functions that manipulate user-defined input, because they are much
less likely to trigger stack overflow.
- They can be turned off compiling with
`-DDISABLE_RECURSIVE_COROUTINES`, falling back to regular recursion,
for debug purposes.
- They support both direct and indirect recursion, i.e. a recursive
coroutine A can recursively call itself, or it can recursively call
another recursive coroutine B, which in turns recursively calls A.
Alessandro Di Federico