I am kinda surprised nobody mentioned Lazy.jl and its macro @forward.
Basically you can do:
import Base: length, getindex, setindex
using Lazy: @forward
struct MyVec <: AbstractVector{Float64}
v::Vector{Float64} # same as Array{Float64, 1}
end
@forward MyVec.v Base.size, Base.getindex, Base.setindex!
For all function you just delegate to the field.