Confusing MethodError message

[knuesel]

The error shown by zeta for unsupported number types is confusing:

julia> using Measurements

julia> zeta(2.0 ± 0.1)
ERROR: MethodError: no method matching zeta(::Measurement{Float64})
Closest candidates are:
  zeta(::Number) at /home/user/.julia/packages/SpecialFunctions/Bdhxh/src/gamma.jl:527
  zeta(::Number, ::Number) at /home/user/.julia/packages/SpecialFunctions/Bdhxh/src/gamma.jl:547
  zeta(::BigFloat) at /home/user/.julia/packages/SpecialFunctions/Bdhxh/src/gamma.jl:465
  ...

It's confusing since there is a candidate zeta(::Number) and

julia> Measurement{Float64} <: Number
true

[giordano]

Well, the method you mentioned throws a MethodError:

SpecialFunctions.jl/src/gamma.jl

Lines 526 to 531 in fc960c6

	function $f(z::Number)
	x = float(z)
	typeof(x) === typeof(z) && throw(MethodError($f, (z,)))
	# There is nothing to fallback to, as this didn't change the argument types
	$f(x)
	end

The case of the zeta function is explicitly mentioned in the documentation of Measurements.jl:

julia> using Measurements, SpecialFunctions

julia> @uncertain zeta(2.0 ± 0.1)
1.645 ± 0.094

[knuesel]

Indeed... Maybe it should throw an ArgumentError instead, with an informative message? Or maybe it's an issue with MethodError itself (discussion on Discourse).

[devmotion]

The confusing MethodError was fixed by #347. Instead of throwing a MethodError manually now zeta(::Number) calls an internal function SpecialFunctions._zeta which uses regular dispatching. With SpecialFunctions 1.7.0:

julia> using Measurements, SpecialFunctions

julia> zeta(2.0 ± 0.1)
ERROR: MethodError: no method matching _zeta(::Measurement{Float64})
Closest candidates are:
  _zeta(::Union{Float64, ComplexF64}) at /home/david/.julia/packages/SpecialFunctions/5CocL/src/gamma.jl:414
  _zeta(::T, ::T) where T<:Union{Float64, ComplexF64} at /home/david/.julia/packages/SpecialFunctions/5CocL/src/gamma.jl:233
  _zeta(::BigFloat) at /home/david/.julia/packages/SpecialFunctions/5CocL/src/gamma.jl:473
  ...
Stacktrace:
 [1] zeta(s::Measurement{Float64})
   @ SpecialFunctions ~/.julia/packages/SpecialFunctions/5CocL/src/gamma.jl:412
 [2] top-level scope
   @ REPL[4]:1

[knuesel]

Indeed that fixes it, thanks!