Export tuple type length function

[NHDaly]

Originally posted by @NHDaly in #32427 (comment)

#32427 added an unexported function, _counttuple(::Type{<:Tuple}) which returns the number of elements in the tuple type.

Can we name this something not private and export it? This is something we use all the time in our code at RelationalAI, where we do a lot of stuff with tuples. It also seems like something that other code will use a lot, like DataFrames, CSV, etc.

In that other comment I suggested arity(::Type{<:Tuple}) as one suggestion. I still like that best, but open to others!

• arity()
• tupletypewidth() / tuple_type_width()
• tupletypecount() / tuple_type_count()
• tuplearity()
• tupletypelength() / tuple_type_length()

[NHDaly]

This was originally proposed as a fast implementation for fieldcount(::Type{<:Tuple}), but it was deemed that adding methods to fieldcount isn't worth the cost for potential dynamic dispatches: #32495.

[sanjibansg]

Can I work in this issue? Please guide me with the required procedures. I am new to this organisation. @NHDaly

[NHDaly]

@vtjnash - what do you say? Do you have a preference on any of the names proposed above? ❤️

It would be great to allow @Kahanikaar to pick this up :)

[NHDaly]

@Kahanikaar - Thanks for offering to help! Welcome to the community! 😁
I may have been a bit over-zealous in adding the good first issue label: I think it would be a good first issue, but it's slightly blocked on a decision to pick a name. 😊

That said, if you want to give this a shot and open a PR, we can always work-shop the name in the PR!

I think resolving this issue would involve starting from this function:

julia/base/tuple.jl

Lines 17 to 20 in 11cbaf6

	# convenience function for extracting N from a Tuple (if defined)
	# else return `nothing` for anything else given (such as Vararg or other non-sized Union)
	_counttuple(::Type{<:NTuple{N,Any}}) where {N} = N
	_counttuple(::Type) = nothing

and renaming it to one of the above choices, and then adding a nice docstring to it! :)

We might also want to add it to the exported names, here:
https://github.com/JuliaLang/julia/blob/master/base/exports.jl

And finally depending on if there are already people relying on the existing name, _counttuple maybe keeping that name as an alias to the new name (i.e. const _counttuple = <new name here>).

Let me know if you have questions!

[sanjibansg]

Initial PR made. Do review @NHDaly @vtjnash

[NHDaly]

Closing this, as fieldcount is now statically inferred in the compiler:
#39755 (comment)
#39755 (comment)