Once example

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once.fl

once func Action() => (i32);
unsafe once func UnsafeAction() => (i32);

structure Token { *i32 tears; i32 value; };
unsafe Token Token::init(*i32 tears, i32 value) override {
    return build Token {
        self.tears = tears;
        self.value = value;
    };
}
void Token::tear(&self) override {
    unsafe { *self->tears = *self->tears + 1; }
}
i32 consume(Token token) { return token.value; }
i32 answer() { return 22; }

unsafe i32 main() {
    i32 tears = 0;
    {
        Token token = Token::init(&raw tears, 20);
        Action action = once [own token]() => (i32) {
            return consume(token);
        };
        if action() != 20 { return 1; }
        if tears != 1 { return 2; }
    }
    if tears != 1 { return 3; }

    {
        Token token = Token::init(&raw tears, 1);
        Action never = once [own token]() => (i32) {
            return consume(token);
        };
    }
    pointer, failure := new<i32>(20);
    if failure != none { return 4; }
    UnsafeAction release = unsafe once [own pointer]() => (i32) {
        i32 value = *pointer;
        free(pointer);
        return value;
    };
    Action direct = answer;
    return release() + direct() + tears - 2;
}