profile better how this module work

[lekoala]

maybe this is a bias introduced by the profiling tool (using xdebug is just slow as hell), but from what i can see, the config api takes a big part from a request

sorting by total self cost, this is what i get for the top functions

this is when there is no write. when the config is being written, we have this : 23k calls to the var export function. that doesn't seem right, how can a function be called that much??

i think it's probably easy to get at least 10ms per request by improving this component

A couple of things to investigate:

• Priority::mergeArray could pass argument as reference to optimize performance
• Not sure why MemoryConfigCollection::get is slow. i'm wondering if checking deprecation at runtime is a good idea for a function called that often
• getClassConfig seems to cache everything alright. maybe the nested array has some hidden cost. trying a cache key with $classKey_$excludeMiddleware should most likely be more performant (not by much, but that thing is called so much that every gain is interesting ;-) )
• For config::inst() probably doing $this->manifests[count($this->manifests) - 1]; count each time is not great. since there is strict control over push/pop of manifest, it would be much better to return the latest manifest directly without doing a count call. again, small optimization, but this is called a lot.

:-) that's just some ideas i get by reading the code, maybe none of this matter but I can give it a try