FName - Pass by value or pass by reference

[Emaer]

@Doumbaga

I’m just curious about which one is more efficient, performance wise.
I don’t think that using a const reference solve my issue, but thank you for the link, it was really interesting.

For 1) Why Epic is usually passing FName by copy in the engine code instead of using const reference ?

For 2) Using a const ref doesn’t change the sizes of a FName reference. So my comparison with a FName pass by value is still the same.

For 3) Even if you use a const reference there is still an indirection.

I think compiler do the work and there is practically no difference in performance.
Im asking because Im sure dealing with FName isnt critical part of your code to worry about performance.

Ad.1) You sure? TotalCommander counts above 500 files with ‘const FName&’ phrase (just in /runtime subdir)
Ad.2) Yes, but const is important part of language. Optimizers loves const

@Jambax

There was quite a lengthy discussion about this a few weeks ago in the UE4 Slackers Discord - the general consensus is that passing by const value is the correct method due to the indirection cost of a reference.
It’s also worth pointing out that FName size actually changes depending on the build type you are using. In Editor they are larger, because they are case-sensitive - whereas outside of editor they are case-insensitive. In Editor they are 12 bytes, but outside of editor they are actually 8 bytes.

Seriously? Discussion about eight-byte structure, which perfectly fits in x64 registers? Lol.