warning when redefining show, Julia >=0.5 only

[stephancb]

Since Julia 0.5 I get (slightly annoying)

WARNING: Method definition show(IO, ....

when redefining the show function of a "with_kw" immutable:

julia> using Parameters

julia> @with_kw immutable Tstmp
           day2000::Int
           msec::Int
       end
Tstmp

julia> Base.show(io::IO, tt::Tstmp) = print(io, "days since 2000-01-01: $(tt.day2000) millisec of day: $(tt.msec)")
WARNING: Method definition show(IO, Main.Tstmp) in module Main at /home/scb/code/julia/pkg/v0.5/Parameters/src/Parameters.jl:375 overwritten at REPL[3]:1.

[mauro3]

Yes, this is expected and is hitting one of 0.5's more controversial features:
JuliaLang/julia#18725

The @with_kw macro also defines a show method:

julia> type A
       a
       b
       end

julia> A(3,4)
A(3,4)

julia> @with_kw type B
       a
       b
       end
B

julia> B(3,4)
B
  a: 3
  b: 4

So if you define your own show method it will overwrite the one of @with_kw and trigger the warning.

Solutions: live with it or remove the show definition from the macro.

[stephancb]

Ok, thanks.

[mauro3]

One solution could be to have several macros, one of which, didn't make a show method. But that does lead to quite a bit more complexity, which I'm hesitant to add. I'll leave this open for now and ponder it some.

[mauro3]

Also you could use https://github.com/Ismael-VC/Suppressor.jl:

julia> using Parameters

julia> @with_kw immutable Tstmp
           day2000::Int
           msec::Int
       end
Tstmp

julia> @suppress_err Base.show(io::IO, tt::Tstmp) = print(io, "days since 2000-01-01: $(tt.day2000) millisec of day: $(tt.msec)")

[mauro3]

Closing this as "won't-fix" as I want to keep the automatically defined show methods.

[juliohm]

Could you please reconsider this issue? I really like the keyword parameters, but I also think that in many cases the user wants to write their own Base.show. Using another package for just hiding the warning seems like hmmm... 👎

I hope the issue won't be ported to Base. Keyword parameters are awesome without shows.

[ChrisRackauckas]

@with_kw_noshow?

[juliohm]

Wonderful!

[mauro3]

Ok.

[mauro3]

This still needs docs, so I'll keep it open for now. But it works:

@with_kw_noshow struct A
a
end

[juliohm]

That is awesome @mauro3 , thanks for adding this feature 🙂

[mauro3]

You're welcome!

[mauro3]

Now also has docs.