On Thu, 05 Aug 2010 15:13:26 -0400, simendsjo <simen.end...@pandavre.com>
wrote:
On 05.08.2010 20:53, Steven Schveighoffer wrote:
On Thu, 05 Aug 2010 14:45:18 -0400, simendsjo
<simen.end...@pandavre.com> wrote:
This is only tested on dmd 2.047 on win7.
According to the spec at http://digitalmars.com/d/2.0/arrays.html:
"Concatenation always creates a copy of its operands, even if one of
the operands is a 0 length array"
But this doesn't seem like the case:
auto a = [0];
auto oldPtr = a.ptr;
assert(a.length == 1);
assert(a.capacity == 3);
a ~= 1;
assert(a.ptr != oldPtr); // Fails - Still the same array
Concatenation is this:
a ~ 1
appending is this:
a ~= 1
Two separate operations, two separate semantics. It might not be easy to
determine that from the spec, but I believe the spec is clear.
-Steve
Hmm... Doing "a = a ~ 1", and it works like specified.
I always assumed that composite operators would mean the same..
That "a += 1" is the same as "a = a + 1" etc.
I cannot find this behavior explained in the spec though..
From the Expression spec, I found that "a op= b" is the same as "a = a
op b" - see "Assignment Operator Expressions".
No mention of a CatAssignExpression behaving differently. Array doesn't
mention anything either.
I found this line in the spec:
"These issues also apply to concatenating arrays with the ~ and ~=
operators."
Where "These issues" refer to reallocating in place (look at the section
for setting the length of an array).
I think this line is in error, as it directly conflicts with the statement:
"Concatenation always creates a copy of its operands, even if one of the
operands is a 0 length array"
I think the line should read:
"These issues also apply to appending arrays with the ~= operator. Note
that the concatenation operator ~ is not affected since it always
reallocates."
I can assure you that the runtime does always make a copy on
concatenation, and always tries to append in place if possible on an
expanding length or an append.
The spec needs some work, but the runtime is correct.
I will file a bug against the spec for you.
-Steve
