add metadata

Project.toml

@@ -1,7 +1,7 @@
 name = "DataAPI"
 uuid = "9a962f9c-6df0-11e9-0e5d-c546b8b5ee8a"
 authors = ["quinnj <[email protected]>"]
-version = "1.10.0"
+version = "1.11.0"
 
 [compat]
 julia = "1"

src/DataAPI.jl

@@ -287,4 +287,14 @@ using a `sink` function to materialize the table.
 """
 function allcombinations end
 
+"""
+    metadata(x)
+
+Return metadata associated with object `x` as an `AbstractDict{String}` object
+(or an object implementing the same interface), or `nothing` if `x` does not support metadata.
+
+Note that some systems, like Arrow.jl, might assume that metadata values are also `String`.
+"""
+metadata(::Any) = nothing
+
 end # module

test/runtests.jl

@@ -9,6 +9,7 @@ end
 Base.size(x::TestArray) = size(x.x)
 Base.getindex(x::TestArray, i) = x.x[i]
 DataAPI.levels(x::TestArray) = reverse(DataAPI.levels(x.x))
+DataAPI.metadata(x::TestArray) = Dict("length" => length(x))
 
 @testset "DataAPI" begin
 
@@ -173,4 +174,9 @@ end
     @test DataAPI.unwrap(missing) === missing
 end
 
+@testset "metadata" begin
+    @test DataAPI.metadata(1) === nothing
+    @test DataAPI.metadata(TestArray([1, 2])) == Dict("length" => 2)
+end
+
 end # @testset "DataAPI"