Everyone,
I recently took the introspection aspects of Julia for a spin and
tried to pick out the values of all the fields of a composite type
that were of a subtype of a certain type. What I observed puzzled me
and after some time staring at the code I constructed the following
minimal example that still exhibits the same odd behaviour.
type Foo{T<:Real}
bar::Array{T,2}
qux::Bool
end
foo = Foo(rand(2, 2), true)
for name in names(foo)
@show name
@show fieldtype(foo, name)
@show issubtype(fieldtype(foo, name), Array)
end
@show issubtype(Array{Float64,2}, Array)
@show issubtype(fieldtype(foo, :bar), Array)
If we run this code using the latest master, we observe:
> julia foo.jl
name => :bar
fieldtype(foo,name) => Array{Float64,2}
issubtype(fieldtype(foo,name),Array) => false
name => :qux
fieldtype(foo,name) => Bool
issubtype(fieldtype(foo,name),Array) => false
issubtype(Array{Float64,2},Array) => true
issubtype(fieldtype(foo,:bar),Array) => true
I really can not grasp why `issubtype` returns `false` for the field
`bar` in the loop, but not when evaluated with its type stand-alone as
on the last line. I am sure that I am missing something here and I
would very much appreciate if someone could tell me what aspect of
Julia introspection that I have yet to understand.
Regards,
Pontus Stenetorp
