Suggestion: Warn on `x -> foo(x)`

[jakobnissen]

It's common to see people do e.g. filter(i -> isodd(i), arr). This is unidiomatic and should be filter(isodd, arr). It seems like it should be easy to add to the linter.

[nsajko]

I think this problem may not be as easy as it seems at first hand, because any type may be callable in Julia and the proposed suggestion only makes sense in general for Function subtypes.

For example:

julia> struct S end

julia> (::S)() = 3

julia> s = S()
S()

julia> f = (() -> s())
#1 (generic function with 1 method)

julia> s() == f()
true

julia> s isa Function
false

julia> f isa Function
true

Docs: https://docs.julialang.org/en/v1/manual/methods/#Function-like-objects

[pfitzseb]

This is only relevant when the higher order function the functor is passed to has a strict type constraints on Function (instead of e.g. Base.Callable).

[nsajko]

This is only relevant when the higher order function the functor is passed to has a strict type constraints on Function

Yes, but this isn't "only" as far as I see. Furthermore, the constraint doesn't need to be on the direct callee - you'd have to check all potential indirect callees for such constraints.

instead of e.g. Base.Callable

Base.Callable is completely undocumented.