Type unstability with args

New to Julia
1

Hello,

I would like to make the following function type stable:

function f(args…)
t = Tuple([arg] for arg in args)
return t
end

f(1,2.0,“s”)

a run from @code_warntype gives me

julia> @code_warntype f2(1,2.0,“s”)
MethodInstance for f2(::Int64, ::Float64, ::String)
from f2(args…) @ Main REPL[40]:1
Arguments
#self#::Core.Const(Main.f2)
args::Tuple{Int64, Float64, String}
Locals
#25::var"#25#26"
t::Tuple{Vararg{Vector}}
Body::Tuple{Vararg{Vector}}
1 ─ %1 = Main.Tuple::Core.Const(Tuple)
│ %2 = Main.:(var"#25#26")::Core.Const(var"#25#26")
│ (#25 = %new(%2))
│ %4 = #25::Core.Const(var"#25#26"())
│ %5 = Base.Generator(%4, args)::Base.Generator{Tuple{Int64, Float64, String}, var"#25#26"}
│ (t = (%1)(%5))
│ %7 = t::Tuple{Vararg{Vector}}
└── return %7

The type of args is inferred correctly. I thought it would be enough to guess the correct type of t but somehow there is a Vararg which pops up.

Any help would be appreciated.

2

The issue is that looping over the tuple results in the element type being inferred as Any. (that could possibly be changed, to be fair).
So, instead of using a for loop, you can access the tuple elements in a different manner. For example, here, I access them by indexing:

function f(args...)
    ntuple(length(args)) do i
        [args[i]]
    end
end

This is type stable.

2 Likes
3

Thank you very much it works !
I was not aware of this method to create ntuple.

4

map should be type stable too

map(args) do x
    [x]
end