On 2/4/2012 2:04 PM, Era Scarecrow wrote:
[...]
struct X {
int i;
pure int squaredPlus(int x) {
return x*x + i
}
alias squaredPlus sqp;
}
X st(15);
writeln(st.sqp(0)); //15
int i1 = st.sqp(10); st.i++;
int i2 = st.sqp(10); st.i++;
int i3 = st.sqp(10); st.i++;
int i4 = st.sqp(10); st.i++;
You can rewrite these like so:
int i1 = sqp(st, 10); st.i++;
int i2 = sqp(st, 10); st.i++;
int i3 = sqp(st, 10); st.i++;
int i4 = sqp(st, 10);
At this point it becomes a little more obvious that these cannot be
reordered because their arguments have a shared dependency, just like
the following cannot be reordered:
int i = 15;
int i1 = i * i; ++i;
int i2 = i * i; ++i;
int i3 = i * i; ++i;
int i4 = i * i;
I hope we all agree that opMult(int, int) is pure, and that is both safe
to reorder its execution with non-dependent args, and unsafe to do so here.
assert(i1 == 100); //pass/fail?
> [...]
Fail. It should be i1 == 115. ;)
Dave
