ambigous method error on missings

[bgctw]

The following code converts from an Vector{Tuple} to a Vector of first entry of the Tuple. I expected that I can access it like a Vector. However, currently it errors with 'method is ambiguous'. How can I make it work?

tvec = allowmissing([(rand(),rand()) for i=1:6]);
tvec[1] = missing
c = mappedarray(x-> ismissing(x) ? missing : first(x),tvec);
c[1:2]

[timholy]

This would be fixed by #34.

[bgctw]

Tested with version MasonProtter@3741807 mentioned in #34

On my Setup (Julia 1.6_RC1on Linux) it still fails:

julia> c[1:2]
ERROR: MethodError: convert(::Type{Union{}}, ::Float64) is ambiguous. Candidates:
  convert(::Type{T}, x::Number) where T<:Number in Base at number.jl:7
  convert(::Type{T}, x::Number) where T<:AbstractChar in Base at char.jl:179
  convert(::Type{C}, c::Number) where C<:Colorant in ColorTypes at /home/twutz/.julia/packages/ColorTypes/RF8lb/src/conversions.jl:74
  convert(::Type{Union{}}, x) in Base at essentials.jl:203
  convert(::Type{T}, arg) where T<:VecElement in Base at baseext.jl:8
  convert(::Type{T}, x) where T<:Observables.Observable in Observables at /home/twutz/.julia/packages/Observables/Yf3xU/src/Observables.jl:52
Possible fix, define
  convert(::Type{Union{}}, ::Number)

[bgctw]

I tried to explicitly fix the return type of the function. But this does not work either.
(Julia 1.6_RC1, ca07b29)

tvec = allowmissing([(rand(),rand()) for i=1:6]);
tvec[1] = missing
function f1(x)::Union{Missing,Float64}
    ismissing(x) ? missing : first(x)
end
c = mappedarray(f1,tvec);
c[1:2]

Interestingly, in the stacktrace, MappedArrays.jl does not appear. Maybe the cause is at a different spot than type inference?

ERROR: MethodError: convert(::Type{Union{}}, ::Float64) is ambiguous. Candidates:
  convert(::Type{T}, x::Number) where T<:Number in Base at number.jl:7
  convert(::Type{T}, x::Number) where T<:AbstractChar in Base at char.jl:179
  convert(::Type{Union{}}, x) in Base at essentials.jl:203
  convert(::Type{T}, arg) where T<:VecElement in Base at baseext.jl:8
Possible fix, define
  convert(::Type{Union{}}, ::Number)
Stacktrace:
 [1] convert(#unused#::Type{Missing}, x::Float64)
   @ Base ./missing.jl:69
 [2] setindex!(A::Vector{Missing}, x::Float64, i1::Int64)
   @ Base ./array.jl:839
 [3] macro expansion
   @ ./multidimensional.jl:860 [inlined]
 [4] macro expansion
   @ ./cartesian.jl:64 [inlined]
 [5] _unsafe_getindex!
   @ ./multidimensional.jl:855 [inlined]
 [6] _unsafe_getindex(#unused#::IndexLinear, A::ReadonlyMappedArray{Missing, 1, Vector{Union{Missing, Tuple{Float64, Float64}}}, typeof(f1)}, I::UnitRange{Int64})
   @ Base ./multidimensional.jl:846
 [7] _getindex
   @ ./multidimensional.jl:832 [inlined]
 [8] getindex(A::ReadonlyMappedArray{Missing, 1, Vector{Union{Missing, Tuple{Float64, Float64}}}, typeof(f1)}, I::UnitRange{Int64})
   @ Base ./abstractarray.jl:1164
 [9] top-level scope
   @ REPL[201]:1