Checked Slices

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// Build: build/flecha build examples/checked_slices.fl -o build/checked_slices
void increment([]i32 values) {
    loop usize i = 0; i < values.len(); i++ {
        values[i]++;
    }
}

i32 sum([]const i32 values) {
    i32 total = 0;
    for (_, value) := range values {
        total = total + value;
    }
    return total;
}

i32 main() {
    [5]i32 values = [10, 20, 30, 40, 50];
    middle := values[1:4]; // Borrows elements 1, 2, and 3; no allocation.
    increment(middle);   // Reborrows for the call; middle remains usable.
    middle.front() = 22;
    last := &middle.back();
    *last = 42;

    []const i32 readonly = middle[:];
    copy := readonly; // Read-only handles can be copied.
    if sum(copy) != 95 { return 1; }
    for (index, value) := range readonly {
        stdoutln(index);
        stdoutln(value);
    }
    // All shared uses ended; mutation through middle is available again.
    moved := middle; // Mutable handles move; middle is no longer usable.
    moved[1]++;
    empty := moved[3:3];
    if empty.len() != 0 { return 2; }

    // The last slice use ended; direct array access is available again.
    if values[1] != 22 or values[2] != 32 or values[3] != 42 { return 3; }
    return 0;
}