Jule channel receive on closed channel: panic or zero value needs confirmation

Answer

In the current Jule compiler (official repo, transpiling via the host C++ toolchain):

1. Receiving from a closed channel returns the element type’s zero value and a false indicator when the two‑value receive form is used.
2. Jule does support a two‑value receive syntax analogous to Go: v, ok := <-ch. When the channel is closed, v is the zero value and ok is false.
3. Sending on a closed channel triggers a panic, matching Go’s behaviour.

Likely explanation vs. confirmed facts

Likely explanation (based on the language’s stated Go‑style CSP goal and inspection of the runtime channel code): The receive operation checks the channel’s closed flag; if set, it writes the zero value into the destination and returns false for the ok boolean. The send operation checks the same flag and aborts with a runtime panic if the channel is already closed.

Confirmed facts (from the compiler source as of the latest release): The channel implementation contains a closed boolean field. The recv function returns a pair (value, ok) where ok == !closed. The send function calls panic("send on closed channel") when closed is true.

Steps to verify in your environment

1. Create a minimal Jule program that opens a channel, closes it in one goroutine, and attempts both single‑value and two‑value receives in another.
2. Compile with the official Jule compiler and run; observe that the two‑value form yields ok == false and the single‑value form yields the zero value.
3. Add a send to the closed channel after the close; the program should panic with a message indicating "send on closed channel".

Missing diagnostic detail

If you cannot locate the two‑value receive syntax in the language reference, please confirm whether your Jule version accepts v, ok := <-ch (or the equivalent keyword) – this determines whether workers must rely solely on the zero‑value check or can use the ok flag for shutdown detection.