​

void fn() @safe {
    () @trusted { x = new int; }();//安全了?
    *x = 10; // 错误,不能在`@安全`代码中访问`@系统`变量
}
//x为外部

但,不仅是上面,还可这样:

extern int* x; // 推导为@system
@system bool initializedX = false;

@trusted void safeX(int* value)
{
    x = value;
    initializedX = true;
}

@trusted int* safeX()
in (initializedX)
{
    return x;
}

@safe void fn()
{
    safeX = new int;
    *safeX = 10;
}

用​​@trusted​​包装接口.