Context Managers

`with (...) { ... }` invokes `__enter__()` on entry and

Path

docs/examples/language/context_managers.gb

Category

Language

__exit__() on every exit path (normal completion,

exception, return, break, continue).

Context managers are a scoped-cleanup construct

distinct from destructors. They never invoke

~ClassName() - end-of-lifetime cleanup is a

separate concern.

Source

import io;

class Transaction {
    string label;

    func Transaction(string label) { this.label = label; }

    func __enter__(): Transaction {
        io.println("begin " + this.label);
        return this;
    }

    func __exit__(): void {
        io.println("commit " + this.label);
    }
}

with (tx = Transaction("write")) {
    io.println("inside " + tx.label);
}

/* __exit__ runs on every exit path - here a break. */
class Span {
    string name;
    func Span(string n) { this.name = n; }
    func __enter__(): Span { return this; }
    func __exit__(): void { io.println("end " + this.name); }
}

for (i in [1, 2, 3]) {
    with (s = Span("iter-" + (i as string))) {
        if (i == 2) {
            break;
        }
        io.println("body " + s.name);
    }
}