Global variables

Use global var for mutable top-level state:

global var requests: Int = 0;

fun recordRequest() {
    requests = requests + 1;
}

The variable is initialized before program execution and remains available for the process lifetime.

Reading and writing a global

global var lastStatus: Int = 0;

fun updateStatus(status: Int) {
    lastStatus = status;
}

fun currentStatus() Int {
    return lastStatus;
}

Prefer explicit state

Global variables hide which code can change a value and make tests harder to isolate. Prefer passing state to functions or storing it in a class:

class Metrics {
    priv requests: Int;

    pub fun record() {
        self.requests = self.requests + 1;
    }

    pub fun count() Int {
        return self.requests;
    }
}

Use a global only when one process-wide mutable value is genuinely part of the program’s design.