On Thursday, 3 March 2016 at 11:40:29 UTC, John Colvin wrote:
On Thursday, 3 March 2016 at 02:03:01 UTC, maik klein wrote:
Consider the following code
void main()
{
import std.stdio;
import std.range: iota, join;
import std.algorithm.iteration: map;
import std.conv: to;
import std.meta: aliasSeqOf, staticMap, AliasSeq;
enum types = "AliasSeq!(" ~ iota(0,10000).map!(i =>
to!string(i)).join(",") ~ ")";
alias t = AliasSeq! (mixin(types));
//alias t1 = aliasSeqOf!(iota(0, 10000));
}
't' compiles on my machine in ~3.5 seconds while 't1' needs ~1
minute to compile. It seems that mixins are just way more
performant than template instantiations. Any ideas why? What
causes the slowdown and what can I improve?
What happens if you add a few extra branches to
std.meta.aliasSeqOf, e.g.
https://github.com/D-Programming-Language/phobos/commit/5d2cdf103bd697b8ff1a939c204dd2ed0eec0b59
Only a linear improvement but maybe worth a try?
I have tried the same thing in general and stuff like this is
always a huge improvement.
In this case it goes down from ~60 seconds to ~3.8 seconds. I
have done the same thing with my compile time map function, which
gave me a drastic improvement.
I think recursion is just really bad in general for compile time
stuff, for example your version
alias t1 = aliasSeqOf!(iota(0, 10000));
compiles in 3.8 seconds and uses roughly 600mb of ram while
alias t1 = aliasSeqOf!(iota(0, 20000));
compiles in 10.2 seconds and uses 1.9gb ram.
The mixin version is always the fastest but it also consumes way
more memory and explodes before 20k elements
