Add const declerations to type aliases

[kunzaatko]

• feat(perf): Add const declarations to type aliases

[kunzaatko]

It should in theory lead to type specialization and avoid runtime dispatch.
It should not change any functionality since the types are not changed elsewhere.

[codecov]

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[kunzaatko]

Could you add the the run benchmark label so that we can see whether it truly makes a difference or the compiler is smart enough to infer the const?

[timholy]

This is only cosmetic, as

julia> using FixedPointNumbers, ColorTypes

julia> FixedColorant{T<:Normed} = Colorant{T}
ColorantNormed (alias for Colorant{T} where T<:Normed)

julia> isconst(Main, :FixedColorant)
true

The key point is that all of these have curly braces {T} in the left-hand side, so Julia knows they refer to types and marks them const.

That said, if you like the code better with the explicit declarations, we can merge this.

[kunzaatko]

Thanks for the explanation!
I do like the code better since I see it often in other packages and consider it a standard that supports explicitness. As a newcomer, one knows that what is declared const is not modified within the rest of the package, however as you say, this would probably madden the compiler and it would not happen anyway.
However you should not feel pressured into merging this if you like the code the other way around.