Measurements.± has already a non-infix operator equivalent: Measurements.measurement, you don’t need to make your own function. But non-infix operator can’t be used as…infix operators, that’s why your attempt to use .mpm wouldn’t work. But you can do
julia> using Measurements: measurement
julia> measurement(10, 1)
10.0 ± 1.0
julia> measurement.([10, 20, 30], [1, 2, 3])
3-element Vector{Measurements.Measurement{Float64}}:
10.0 ± 1.0
20.0 ± 2.0
30.0 ± 3.0