Generic fallbacks for type reflection

[BeastyBlacksmith]

I think it would make sense for the reflection functions on types such as isstructtype, isabstracttype, etc. to have the generic fallback

isstructtype(x) = false

For example getting the names of all types defined in a module via

filter(x->(x = getproperty(MODULE, x); isstructtype(x)), names(MODULE, all = true))

currently errors.

I'd happy to make a PR if this would be a worthwhile addition to Base.

[aviatesk]

FWIW, isstructtype now doesn't throw MethodError when taking arbitrary type object:

julia/base/reflection.jl

Line 499 in 6bea8e3

function isstructtype(@nospecialize t)

To me, the essential problem here seems to be that actual method signatures of those reflection tools are sometimes not reflected in documentation. So I guess it would be more appropriated if your PR takes a direction of syncing the actual method signatures with those described in docstrings.

[JeffBezanson]

AFAICT isstructtype already returns false for arbitrary objects; what error are you getting?

julia> isstructtype(false)
false

julia> isstructtype(nothing)
false

julia> isstructtype("")
false

[aviatesk]

AFAICT isstructtype already returns false for arbitrary objects

The method signature of isstructtype was widened fairly recently in #43087 in order to make its @nospecialize annotation to be functional (although we also fixed that need in #43113 too).

[BeastyBlacksmith]

what error are you getting?

At least on 1.7.0 i get

ERROR: MethodError: no method matching isstructtype(::IdDict{Any, Any})
Closest candidates are:
  isstructtype(::Type) at ~/.asdf/installs/julia/1.7.0/share/julia/base/reflection.jl:499
Stacktrace:
 [1] (::var"#5#6")(x::Symbol)
   @ Main ./REPL[5]:1
 [2] filter(f::var"#5#6", a::Vector{Symbol})
   @ Base ./array.jl:2484
 [3] top-level scope
   @ REPL[5]:1

[inkydragon]

v1.7.0:

julia/base/reflection.jl

Line 499 in 3bf9d17

function isstructtype(@nospecialize(t::Type))

@nospecialize(t::Type) -> @nospecialize t: #43087