@trusting generic functions

[ag0aep6g via Digitalmars-d-learn]

On 05/28/2016 02:43 PM, Lodovico Giaretta wrote:
> struct S1
> {
>      int doSomething() @safe
>      {
>          // do something safely
>          return 1;
>      }
> }
>
> struct S2
> {
>      int doSomething() @system
>      {
>          // do something usafe
>          return 2;
>      }
> }
>
> auto doSomethingDumb(T)(ref T t)
> {
>      T* pt = &t;
>      return pt.doSomething();
> }
>
> auto s1 = S1();
> auto s2 = S2();
> auto x = doSomethingDumb(s1); // this call should be possible in @safe code
> auto y = doSomethingDumb(s2); // this should only be possible in @system
> code

I'm not sure if should mention it, but there is this little trick:

----
auto doSomethingDumb(T)(ref T t)
{
     T* pt;
     () @trusted { pt = &t; } (); /* Ok, because the reference is never 
returned. NOTE: DON'T RETURN THIS POINTER! */
     return pt.doSomething();
}
----

Though in cases like this it's kind of an anti-pattern. The trusted code 
itself isn't actually safe, but the compiler thinks so. So you have to 
manually verify that doSomethingDumb is safe, even though it's not 
marked @trusted. That's pretty bug-prone.