On 09/29/2012 06:26 PM, Maxim Fomin wrote:
On Saturday, 29 September 2012 at 16:05:03 UTC, ixid wrote:
This behaviour seems inconsistent and unintuitive:
void main() {
int[3] a = [1,2,3];
a = [4, a[0], 6];
struct S {
int a, b, c;
}
S s = S(1,2,3);
s = S(4, s.a, 6);
assert(a == [4,1,6]);
assert(s == S(4,4,6));
}
Setting the struct writes s.a before evaluating it while the reverse
is true of the array assignment. Using DMD 2.0.60. GDC does what I'd
expect and gives both as 4,1,6.
I think this is notorious "i = ++i + ++i".
There is only one mutating sub-expression.
Statement s = S(4, s.a, 6) writes to s object and simultaneously reads it.
http://dlang.org/expression.html states that assign expression is
evaluated in implementation defined-manner and it is an error to depend
on things like this.
No evaluation order of the assignment expression can possibly lead to
this result. This seems to be a DMD bug.
