On Monday, 19 August 2013 at 12:55:54 UTC, bearophile wrote:
The problem is that while writing down the proof of the purity
of foo3 is probably not too much hard, later the D compiler is
not able to verify such proof.
Bye,
bearophile
Right, that is pretty much it. EG:
//----
import core.stdc.stdlib;
int* myPureFun(int i) pure
{
auto p = cast(int*) malloc(int.sizeof);
if (!p) assert(0);
*p = i;
return p;
}
//----
I can solve this the same way (kind of) as with safety, by
marking the function as I can mark a function as trusted, by
casting the function as pure:
//----
int* myPureFun(int i) pure
{
alias extern (C) void* function(size_t) pure PureF_t;
auto p = cast(int*) (cast(PureF_t)&malloc)(int.sizeof);
if (!p) assert(0);
*p = i;
return p;
}
//----
A basic "I know what I'm doing compiler" kind of assertion.
My only issue with doing this is I'm afraid it might be wrong: A
"trusted" function means nothing to the compiler.
However, in the above example, I *marked* malloc as pure, and
even though "myPureFun" is conceptually pure, *malloc* remains
impure, and I don't know how the compiler deals with being told
it is pure.
Is that code snippet wrong?
