On Wednesday, 28 May 2014 at 14:36:25 UTC, Chris wrote:
I use Appender to fill an array. The Appender is a class
variable and is not instantiated with each function call to
save instantiation. However, the return value or the function
must be dup'ed, like so:
Appender!(MyType[]) append;
public auto doSomething() {
scope (exit) { // clear append }
// ... do something
append ~= item;
return (append.data).dup
}
My question is whether I save anything with Appender as a class
variable here. I have to .dup the return value (+ clear the
Appender). If I had a new Appender with each function call, it
might be just as good.
public auto doSomething() {
Appender!(MyType[]) append;
// ....
return append.data.
}
Right or wrong?
You might save a little because you avoid the cost of "growing"
your appender repeatedly: Once the appender has come to
"maturity", it will very likely stop growing.
At that point, you only pay for *1* allocation per call to
doSomething. Further advantages include:
- dup has "APPENDABLE" info (whereas appender.data does not).
- less wasted memory: dup uses no more memory than it has to,
whereas Appender may over-allocate, depending on how you fill it.
The "downside" to your approach is that you keep a handle on a
buffer that can grow, but never shrink. If a at a certain point,
you have to process some particularly large input, then you'll
consume excessive amounts of memory.
