Andrei Alexandrescu wrote:
On 6/17/11 1:56 AM, Kagamin wrote:
Andrei Alexandrescu Wrote:
This has sparked an interesting discussion, to which I added my
bit.
int fun(int a) pure { if (a> 10) writeln("I'm impure); }
As I understand, even if some calls to a function have some
repeatability properties, this doesn't mean the function is pure. In
this example fun is obviously impure. Here one can talk about
allowing to call impure functions from pure ones, but that's a way
different task.
Right. I gave that example within the context of the discussion, which
considered purity a path-sensitive property. By that definition, if fun
is provably never invoked with a > 10, then it's effectively pure.
Andrei
And that's an interesting thing about CTFE: although it can never do
anything impure, it can call impure functions, provided it avoids the
impure bits of them:
int foo(int n)
{
static int x = 56;
if (n<10)
return n;
++x;
return x;
}
static assert(n(5) == 5);
Likewise, it can never doing anything unsafe, but can call unsafe functions.
bool bar(int n)
{
if (n < 2) return true;
corruptTheStack();
return false;
}
static assert(bar(1));
