# How to define function signature with nested types of tuples, functions, vectors, and reals?

**URL:** <https://discourse.julialang.org/t/how-to-define-function-signature-with-nested-types-of-tuples-functions-vectors-and-reals/48739>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [October 21, 2020, 11:44am UTC](https://discourse.julialang.org/t/how-to-define-function-signature-with-nested-types-of-tuples-functions-vectors-and-reals/48739 "2020-10-21T11:44:31Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![kapple](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kapple/32/218915_2.png) [@kapple](https://discourse.julialang.org/u/kapple)\
**Post date:** [October 21, 2020, 11:44am UTC](https://discourse.julialang.org/t/how-to-define-function-signature-with-nested-types-of-tuples-functions-vectors-and-reals/48739/1 "2020-10-21T11:44:31Z")

</div>

What am I doing wrong here?

```julia
julia> function fcn(xvec::AbstractVector{T}, ytup::Tuple{V}, ztup::Tuple{V}) where {T <: Real, V <: AbstractVector{T}}
       @show typeof(xVec)
       @show typeof(ytup)
       @show typeof(ztup)
       end
fcn (generic function with 1 method)

julia> fcn([1, 2, 3], ([1, 2, 3], [4, 5, 6]), ([7, 8, 9], [10, 11, 12]))
ERROR: MethodError: no method matching fcn(::Array{Int64,1}, ::Tuple{Array{Int64,1},Array{Int64,1}}, ::Tuple{Array{Int64,1},Array{Int64,1}})
Closest candidates are:
  fcn(::AbstractArray{T,1}, ::Tuple{V}, ::Tuple{V}) where {T<:Real, V<:AbstractArray{T,1}} at REPL[39]:1
Stacktrace:
 [1] top-level scope at REPL[40]:1

```

---

<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [October 21, 2020, 11:58am UTC](https://discourse.julialang.org/t/how-to-define-function-signature-with-nested-types-of-tuples-functions-vectors-and-reals/48739/2 "2020-10-21T11:58:43Z")

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Problem 1: You are over-typing your code 😉

Problem 2:

```julia
julia> (2.1,) isa Tuple{Float64}
true

julia> (2.1,3.0) isa Tuple{Float64}
false

```

So `Tuple{V}` can only have a single element.

This works, but only for length-2 tuples:

```julia

function fcn(xvec::AbstractVector{T}, ytup::Tuple{V,V}, ztup::Tuple{V,V}) where {T <: Real, V <: AbstractVector{T}}
    @show typeof(xvec)
    @show typeof(ytup)
    @show typeof(ztup)
end

```

You also have a typo `xVec` → `xvec`.

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<div class="post-metadata">

**Author:** ![simeonschaub](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/simeonschaub/32/216566_2.png) [@simeonschaub](https://discourse.julialang.org/u/simeonschaub)\
**Post date:** [October 21, 2020, 12:04pm UTC](https://discourse.julialang.org/t/how-to-define-function-signature-with-nested-types-of-tuples-functions-vectors-and-reals/48739/3 "2020-10-21T12:04:08Z")

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To make this example work as you intended, you probably want to use either `Tuple{Vararg{V}}`, or `NTuple{N,V} where N`, which will work for tuples of an arbitrary number of elements `<:V`.

---

<div class="post-metadata">

**Author:** ![kapple](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kapple/32/218915_2.png) [@kapple](https://discourse.julialang.org/u/kapple)\
**Post date:** [October 21, 2020, 12:47pm UTC](https://discourse.julialang.org/t/how-to-define-function-signature-with-nested-types-of-tuples-functions-vectors-and-reals/48739/4 "2020-10-21T12:47:51Z")

</div>

Thank you both of you!

What about here?

```julia
function fcn(TupVecs::NTuple{N, V}) where {N, V <: AbstractVector}
	x = 1
	for nVec ∈ eachindex(TupVecs)
		y = TupVecs[nVec][2]
		println(y)
	end
end

function fcn(TupFcns::NTuple{N, F}) where {N, F <: Function}
	x = 1
	for nFcn ∈ eachindex(TupFcns)
		y = TupFcns[nFcn](x)
		println(y)
	end
end

TupVecs = (
	[1, 3, 5],
	[1, 4, 6, 9],
	[1, 5]
)

TupFcns = (
	x -> x^2,
	x -> x^3,
	x -> x^4
)

fcn(TupVecs) # works fine
fcn(TupFcns) # method error

```

Edit: I’m going to stick with vectors of functions and vectors, instead of tuples of functions and vectors.