It's a hot code reloading proof of concept. Hot potato get it? No. Good.
First nimble install https://github.com/beef331/potato or add a requires "https://github.com/beef331/potato >= 0.1.2" to the .nimble file.
Add the following to config.nims
when appType == "lib":
--nimMainPrefix="libpotato"Following that import potato in the main project file.
Now one can annotate any global variables with {.persistent.} these variables will as the name implies persist across reloads.
Any global code should be non blocking as the potato library calls a specific entry procedure.
This entry procedure's signature is proc potatoMain() {.exportc, dynlib.} and must be declared.
potatoMain is called inside a while loop meaning it must not block as that will stop the hot code reloading.
Finally the program must be compiled with -d:hotPotato -d:useMalloc.
This library uses the environmental variable POTATOWATCHER to watch a program.
The first parameter is the path to the dynamic library to watch.
Following that is a command which dumps all the dependencies of the project.
This watcher must communicate to the environmental variable PORTATO port TCP messages.
src/potato/commands.nim contains the commands which potato watches for.
These are sent as single byte messages.
There are two signatures which the Potato searches for for (de)serialisation:
proc serialise*(src: T, root: JsonNode): JsonNode
proc deserialise*(dest: var T, state: var DeserialiseState, current: JsonNode)
serialise returns the JsonNode of the data to write. Global state can be added to root this is how cyclical graphs are broken by default.
deserialise writes to dest, current stores the data which is extracted to assign to dest.
Since there is no way to recover the type from inheritance migration of inheritance object is disabled by default.
There is not a clean way to migrate them consistently pointer procedures are not migrated.
Which means you must update where pointer procedures point to on reload.
In the future one could read the symbol table of a binary to migrate pointers though this causes an issue with anonymous procedures.
It is suggested to use enums into a global constant array or similar to make dispatch static as it not rely on runtime information.
As of now potatowatcher is a Linux only file watcher. In the future it makes more sense to use fswatch for cross-platform file watching.