# Is there a way to preserve overwritten method?

**URL:** <https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551>\
**Category:** General Usage\
**Created:** [November 15, 2018, 8:03am UTC](https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551 "2018-11-15T08:03:44Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![Liso](https://avatars.discourse-cdn.com/v4/letter/l/898d66/32.png) [@Liso](https://discourse.julialang.org/u/Liso)\
**Post date:** [November 15, 2018, 8:03am UTC](https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551/1 "2018-11-15T08:03:44Z")

</div>

I was thinking about [switch proposal](https://discourse.julialang.org/t/why-so-complex-representation-of-a-char/17052/47)…

We have complex info in REPL about character:

```julia
julia> 'a'
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)

```

If I want to avoid it I could do

```julia
julia> import Base.show

julia> show(io::IO, ::MIME{Symbol("text/plain")}, c::Char) = show(io, c)
show (generic function with 296 methods)

julia> 'a'
'a'

```

but if I want to have possibility to switch it on I need to remember old functionality. This doesn’t work:

```julia
julia> oldfnc(io::IO, m::MIME{Symbol("text/plain")}, c::Char) = show(io, m, c);

julia> oldfnc(stdout, MIME{Symbol("text/plain")}(), 'a')
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
julia> import Base.show

julia> show(io::IO, ::MIME{Symbol("text/plain")}, c::Char) = show(io, c)
show (generic function with 296 methods)

julia> oldfnc(stdout, MIME{Symbol("text/plain")}(), 'a')
'a'

```

this naive experiment doesn’t work either

```julia
julia> mm = collect(methods(show, [IO, MIME{Symbol("text/plain")}, Char]))[1]
show(io::IO, ::MIME{Symbol("text/plain")}, c::T) where T<:AbstractChar in Base at char.jl:281

julia> mm('a')
ERROR: MethodError: objects of type Method are not callable

```

---

<div class="post-metadata">

**Author:** ![jling](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jling/32/212909_2.png) [@jling](https://discourse.julialang.org/u/jling)\
**Post date:** [November 15, 2018, 8:48am UTC](https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551/2 "2018-11-15T08:48:49Z")

</div>

Interesting. Do you know what function is being called when we put `'a'` into the REPL?

Because `Base.show` is not the function out side of `'a'`

```nohighlight
julia> Base.show('a')
'a'

julia> 'a'
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)

julia> dump('a')
Char 'a'

julia> eval('a')
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)

julia> dump(eval('a'))
Char 'a'

```

---

<div class="post-metadata">

**Author:** ![Liso](https://avatars.discourse-cdn.com/v4/letter/l/898d66/32.png) [@Liso](https://discourse.julialang.org/u/Liso)\
**Post date:** [November 15, 2018, 9:21am UTC](https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551/3 "2018-11-15T09:21:13Z")

</div>

It is `Base.show` , but it have more than 200 methods, so you need to call proper one 🙂

Try this:

```julia
julia> show(stdout, MIME{Symbol("text/plain")}(), 'a')
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)

```

BTW you could also look at source code:

```julia
julia> @less show(stdout, MIME{Symbol("text/plain")}(), 'a')

```

---

<div class="post-metadata">

**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [November 15, 2018, 10:03am UTC](https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551/4 "2018-11-15T10:03:37Z")

</div>

It’s pretty easy with Revise & Rebugger:

```julia
julia> using Revise, Rebugger

julia> m = @which show(stdout, MIME("text/plain"), 'a')
show(io::IO, ::MIME{Symbol("text/plain")}, c::T) where T<:AbstractChar in Base at char.jl:281

julia> ex = Revise.get_def(m)
[ Info: tracking Base
:(function show(io::IO, ::@MIME_str("text/plain"), c::T) where T <: AbstractChar
      show(io, c)
      if !(ismalformed(c))
          print(io, ": ")
          if isoverlong(c)
              print(io, "[overlong] ")
              u = decode_overlong(c)
              c = T(u)
          else
              u = codepoint(c)
          end
          h = string(u, base=16, pad=if u ≤ 0xffff
                          4
                      else
                          6
                      end)
          print(io, if isascii(c)
                  "ASCII/"
              else
                  ""
              end, "Unicode U+", h)
      else
          print(io, ": Malformed UTF-8")
      end
      abr = Unicode.category_abbrev(c)
      str = Unicode.category_string(c)
      print(io, " (category ", abr, ": ", str, ")")
  end)

julia> Core.eval(Base, convert(Expr, Rebugger.rename_method(ex, :oldshow, nothing)))
oldshow (generic function with 1 method)

julia> Base.oldshow(stdout, MIME("text/plain"), 'a')
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)

```

---

<div class="post-metadata">

**Author:** ![jlapeyre](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jlapeyre/32/4514_2.png) [@jlapeyre](https://discourse.julialang.org/u/jlapeyre)\
**Post date:** [November 15, 2018, 11:00am UTC](https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551/5 "2018-11-15T11:00:23Z")

</div>

Hmm. Maybe I need a newer (or older snapshot)…

```julia
  | | |_| | | | (_| | | Version 1.1.0-DEV.542 (2018-10-25)
 _/ |\ __'_|_|_|\__'_| | Commit 36e21d47b5 (21 days old master)

julia> using Revise; using Rebugger

julia> m = @which show(stdout, MIME("text/plain"), 'a')
show(io::IO, ::MIME{Symbol("text/plain")}, c::T) where T<:AbstractChar in Base at char.jl:292

julia> ex = Revise.get_def(m)
[ Info: tracking Base
ERROR: KeyError: key "/home/lapeyre/.local/julias/julia-1.1.0-DEV.542/share/julia/base/char.jl" not found
Stacktrace:
 [1] getindex at ./dict.jl:478 [inlined]
 [2] macro expansion at ./logging.jl:313 [inlined]
 [3] #get_def#53(::Set{String}, ::Function, ::Method) at /home/lapeyre/.julia/packages/Revise/xO23U/src/Revise.jl:628
 [4] get_def(::Method) at /home/lapeyre/.julia/packages/Revise/xO23U/src/Revise.jl:606
 [5] top-level scope at none:0

```

---

<div class="post-metadata">

**Author:** ![tim.holy](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tim.holy/32/52_2.png) [@tim.holy](https://discourse.julialang.org/u/tim.holy)\
**Post date:** [November 15, 2018, 11:06am UTC](https://discourse.julialang.org/t/is-there-a-way-to-preserve-overwritten-method/17551/6 "2018-11-15T11:06:35Z")

</div>

Seems like a path issue; I haven’t had anyone report one of those in a while. Please open a Revise issue and report your findings while following [these tips](https://timholy.github.io/Revise.jl/stable/config.html#Fixing-a-broken-or-partially-working-installation-1).