Pure, Nothrow in Generic Programming

[Andrei Alexandrescu]

Walter Bright wrote:
> dsimcha wrote:
>> I think you misunderstood the argument.  memcmp() could be @trusted if 
>> functions
>> only need to be safe when passed valid parameters, though I don't 
>> necessarily
>> agree that this makes sense.  I was thinking memcmp() shouldn't even 
>> be marked
>> @trusted because it's so easy to invoke undefined behavior by passing 
>> incorrect
>> parameters.  This would mean that, if opCmp() uses it, opCmp() 
>> couldn't be marked
>> as @safe.
> 
> memcmp() could be marked @trusted, but it should not be. This is because 
> @trusted functions can be called by @safe ones, but there's no way that 
> an @safe function can guarantee it sends memcmp() arguments that will 
> work safely with memcmp().
> 
> Whoever calls memcmp() can be marked @trusted.

Hm, if we think of it, memcmp can be @safe no problem. This is beacuse 
it oly reads stuff. There are three possible outcomes:

a) valid addresses, all's fine

b) incorrect addresses within the application, erroneous result returned

c) incorrect addresses outside the application, segfault

None of the above is unsafe. So memcmp is safe. (In contrast, memcpy is 
not). Color me surprised but convinced.


Andrei