Wiping modules and persistent Base.show

General Usage
2

In the latter case you are adding a new method to an existing function, not defining a new function. Methods in Julia have no notion of scope, a given function always refers to the same methods, regardless of from where it is called. This is actually a feature, because it’s one of the the main reason Julia’s multiple dispatch is so powerful for generic code.

For your particular use case you could perhaps use Base.delete_method, but note that this is an internal function, so it might break in future Julia versions:

julia> Base.show(io::IO, ::MIME"text/html", i::Int) = print(io, "<span>Int: $i</span>")

julia> repr(MIME("text/html"), 1)                             "<span>Int: 1</span>"

julia> Base.delete_method(which(show, (IO, MIME"text/html", Int)))

julia> repr(MIME("text/html"), 1)                             ERROR: MethodError: no method matching show(::IOBuffer, ::MIME{Symbol("text/html")}, ::Int64)
Closest candidates are:
  show(::IO, ::AbstractString, ::Any) at ~/.julia/juliaup/julia-1.7.0+0~aarch64/share/julia/base/multimedia.jl:111
  show(::IO, ::MIME{Symbol("text/plain")}, ::Any) at ~/.julia/juliaup/julia-1.7.0+0~aarch64/share/julia/base/multimedia.jl:47
  show(::IO, ::MIME{Symbol("text/csv")}, ::Any) at ~/.julia/juliaup/julia-1.7.0+0~aarch64/share/julia/stdlib/v1.7/DelimitedFiles/src/DelimitedFiles.jl:829
  ...
Stacktrace:
 [1] __binrepr(m::MIME{Symbol("text/html")}, x::Int64, context::Nothing)
   @ Base.Multimedia ./multimedia.jl:159
 [2] _textrepr(m::MIME{Symbol("text/html")}, x::Int64, context::Nothing)
   @ Base.Multimedia ./multimedia.jl:151
 [3] repr(m::MIME{Symbol("text/html")}, x::Int64; context::Nothing)
   @ Base.Multimedia ./multimedia.jl:147
 [4] repr(m::MIME{Symbol("text/html")}, x::Int64)
   @ Base.Multimedia ./multimedia.jl:147
 [5] top-level scope
   @ REPL[25]:1

Also keep in mind that you can’t revert to the previous definition if you completely overwrite a previously defined method. It’s also still type piracy, so it’s definitely possible that such workarounds result in weird bugs or even segfaults and you are likely to encounter excessive compile times due to method invalidatioms.

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