use ternery instead of ifelse since ifelse force evaluation of the RHS

[KristofferC]

Made on top of #77 to avoid some merge conflicts and have up to date benchmarks.

I was looking at why the following benchmark allocates:

julia> using StyledStrings

julia> styles = Pair{Symbol, Any}[:face => :green]
1-element Vector{Pair{Symbol, Any}}:
 :face => :green

julia> face = StyledStrings.getface(styles);

julia> using BenchmarkTools

julia> @btime merge($face, $face)
  19.266 ns (2 allocations: 32 bytes)

With the following PR we instead get

julia> @btime merge($face, $face)
  13.388 ns (0 allocations: 0 bytes)

The benchmark in #75

goes from

  8.654 ms (202611 allocations: 16.62 MiB)

to

  7.972 ms (148360 allocations: 15.72 MiB)

Not a huge speedup but quite a big reduction in allocations which might be useful as other things improve.

I am not 100% sure why this is needed but I typically find the compiler optimizes better with ternary ? over ifelse.

[tecosaur]

Interesting, since there's no computation to be done I simply assumed that ifelse would be equivalent to an actual branch.

[KristofferC]

This is just a guess but the field on the RHS for e.g. underline is not very well-typed so accessing that could have some cost? Not sure..

[KristofferC]

FWIW, I would write this something like

abheight = isnothing(bheight) ? aheight :
           isnothing(aheight) ? bheight :
           bheight isa Int    ? bheight :
           aheight isa Int    ? round(Int, aheight * bheight) :
                                aheight * bheight

I haven't really seen Julia code that puts the body of an if on the same line as the condition, instead people typically use terneries in cases like this from my experience.

[tecosaur]

I have seen that pattern a bit, but I can't say I'm a fan of it. Perhaps it's a bit selfish of me, but I'm rather a fan of (if cond val otherwise) and (cond ...) forms and so like to use them over ternaries in projects where I'm the primary author.

I'm also a fan of consistency, and there are nine other one-line if ... else ... end statements floating around already.