Hygiene of named function objects

[Roger-luo]

shouldn't this macro have no effect?

macro noeffect(e)
    return e
end

but it raises error if you use it to this function

struct foo
end

@noeffect function (f::foo)()
   println("no effect")
end

ERROR: LoadError: syntax: "Main.f" is not a valid function argument name

Version Info

Julia Version 0.6.0
Commit 9036443 (2017-06-19 13:05 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i5-4200M CPU @ 2.50GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Haswell)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, haswell)

[KristofferC]

julia> @macroexpand @noeffect function (f::foo)()
          println("no effect")
       end
:(function (Main.f::Main.foo)()
      #= REPL[5]:2 =#
      (Main.println)("no effect")
  end)

julia> macro noeffect2(e)
           return esc(e)
       end
@noeffect2 (macro with 1 method)

julia> @macroexpand @noeffect2 function (f::foo)()
          println("no effect")
       end
:(function (f::foo)()
      #= REPL[7]:2 =#
      println("no effect")
  end)

See https://docs.julialang.org/en/stable/manual/metaprogramming/#Hygiene-1

Please use the forum at https://discourse.julialang.org list for usage question

[mbauman]

I agree that this seems to be a usage question — and using esc is definitely the right answer.

But it does seem like there's an issue here. I would expect the hygiene of (f::T)() = f to behave similarly to g(f::T) = f. You're naming a local argument. Compare:

julia> @macroexpand @noeffect (f::foo)() = f
:((Main.f::Main.foo)() = begin
          #= REPL[4]:1 =#
          Main.f
      end)

julia> @macroexpand @noeffect g(f::Foo) = f
:((Main.g)(#5#f::Main.Foo) = begin
          #= REPL[6]:1 =#
          #5#f
      end)

[JeffBezanson]

Agreed, this is a hygiene bug.