Return the list of elements in array which occur more than once.

Return the names of fields defined in fdef.

Add fields to a type definition. Fields format: :(fieldname::Type).

@with_fields atypename fields...

Macro to define an abstract type atypename that automatically adds fields to its subtypes. The subtypes are declared using the macro @atypename.

Examples:

julia>  @with_fields abs_type a::Int b
julia>  @abs_type struct mystruct
            c::Float64
        end

julia> fieldnames(mystruct)
(:c, :a, :b)

julia> fieldtypes(mystruct)
(Float64, Int64, Any)

julia> mystruct <: abs_type
true


julia> abstract type supertype end
julia> @with_fields abs_type <: supertype field_a field_b
julia> abs_type <: supertype
true