BUG: strange error when using `methods` function

[sglyon]

Consider this very dumb example:

julia> g(x, y) = println("$(typeof(x))\t$(typeof(y))")
g (generic function with 1 method)

julia> g(1.0, 2)
Float64 Int64

julia> methods(g)
#1 method for generic function "g":
g(x,y) at none:1

julia> g(x::Vector, y::Real) = println("Vector and Real")
g (generic function with 2 methods)

julia> g([1.0], 2.0)   # so we know it works
Vector and Real

julia> methods(g)
#2 methods for generic function "g":
gError showing value of type MethodTable:
ERROR: type DataType has no field body
 in show at show.jl:80 (repeats 2 times)
 in print_to_string at ./string.jl:24
 in argtype_decl at methodshow.jl:18
 in arg_decl_parts at methodshow.jl:30
 in show at methodshow.jl:36
 in show_method_table at methodshow.jl:61
 in show at methodshow.jl:74
 in anonymous at show.jl:1107
 in with_output_limit at ./show.jl:1084
 in showlimited at show.jl:1106
 in writemime at replutil.jl:2
 in display at REPL.jl:118
 in display at REPL.jl:121
 in display at multimedia.jl:149
 in print_response at REPL.jl:140
 in print_response at REPL.jl:125
 in anonymous at REPL.jl:587
 in run_interface at ./LineEdit.jl:1377
 in run_interface at /usr/local/julia/usr/lib/julia/sys.dylib
 in run_frontend at ./REPL.jl:819
 in run_repl at ./REPL.jl:170
 in _start at ./client.jl:399
 in _start at /usr/local/julia/usr/lib/julia/sys.dylib

Any idea why this is happening?

[stevengj]

I ran into this earlier today. The error originates in:

show(io::IO, x::TypeConstructor) = show(io, x.body)

I'm not actually sure what TypeConstructor is, but the odd thing is that sometimes it works, depending on exactly what order I initialize things. Also, inserting a dump(x) into this method seems to indicate that x.body exists.

@JeffBezanson, isn't TypeConstructor some kind of internal magic? How should we print it if it is encountered in a method table?

[vtjnash]

I think I usually see TypeConstructors show up in conjunction with typealiases:

julia> AbstractVector|>typeof
TypeConstructor

[stevengj]

And yet AbstractVector.body is defined and gives AbstractArray{T,1}.

[stevengj]

The exception message above makes it seem like the TypeConstructor got converted to a DataType somehow; is there some kind of race condition here?

[vtjnash]

should now be fixed by bd7d3f5