[feature] create setTime function

[aymericbouzy]

This increases the performance of startOf / endOf by a factor of about 90 for 'day'.

NB : This is my first PR, i'm not sure what I should do, especially regarding proving my call about this performance gain. I see there is a benchmark folder, but I don't know what to do about it. I have run grunt tests successfully on my computer.

[jsf-clabot]

All committers have signed the CLA.

[aymericbouzy]

#3619

[icambron]

Seems like the hour case should be this.setTime(this, this.hour(), 0, 0, 0), etc

[aymericbouzy]

True! I also need to benchmark the functions setMinutes(minutes, seconds, milliseconds) and setSeconds(seconds, milliseconds) to see if they are even more efficient.

[icambron]

This could use some benchmarks. Do you mind adding one? They run via grunt benchmarks.

[ichernev]

@aymericbouzy can you please add a simple benchmark as @icambron pointed out. Also, why stop there -- can't we use this setTime to speed up other cases as well. Of course the benchmark will show, but its minimal amount of code and looks like massive improvements of speed, so I don't see why not.

Also when we go immutable it will be much more pronounced.

[aymericbouzy]

Hi @ichernev, sorry for the delay, I've been busy and open source contribution is quite new to me. I'll look into this later today.

[aymericbouzy]

It seems my code does not speed things up when ran with command grunt benchmark. It has significant impact on my iOS React Native App though, which runs with JavaScriptCore if I'm not mistaken. I don't know how to run benchmarks using different Javascript engines. I'm really a beginner on all these subjects.

Does anyone know if I can ask grunt to run the benchmark task using a different engine ? I haven't found anything about this yet in the documentation. Otherwise, I guess we can close this PR for now.

[ichernev]

@aymericbouzy from my cursory understanding of the matter, you can not run grunt benchmark with JavaScriptCore. Maybe you can redo your tests in a clean way to make 100% certain that this particular change speeds up your code.

We've always wanted to remove this crazy case fall through, and we'll certainly like to have it in v3, so I'll merge it anyway. Just make sure to fix all cases (not just date).

[marwahaha]

Thanks for this, and sorry it never got merged. I'm going to take #4338 which will supersede this one.

[aymericbouzy]

It's fine, I never took the time to finish this PR anyway 🤗