#[post_upgrade]Expand description
Register the canister_post_upgrade entry point of a canister.
This attribute macro will export the function canister_post_upgrade
in the canister module.
The function under this attribute must have no return value.
Each canister can only have one canister_post_upgrade entry point.
ยงExample
#[post_upgrade]
fn post_upgrade_function() {
// ...
}