add Cols (#18)

Author: bkamins

Project.toml

@@ -1,7 +1,7 @@
 name = "DataAPI"
 uuid = "9a962f9c-6df0-11e9-0e5d-c546b8b5ee8a"
 authors = ["quinnj <[email protected]>"]
-version = "1.2.0"
+version = "1.3.0"
 
 [compat]
 julia = "1"

src/DataAPI.jl

@@ -117,4 +117,14 @@ struct All{T<:Tuple}
     All(args...) = new{typeof(args)}(args)
 end
 
+"""
+    Cols(cols...)
+
+Select the union of the selections in `cols`. If `cols == ()`, select no columns.
+"""
+struct Cols{T<:Tuple}
+    cols::T
+    Cols(args...) = new{typeof(args)}(args)
+end
+
 end # module

test/runtests.jl

@@ -70,16 +70,18 @@ end
 
 end
 
-@testset "All" begin
+@testset "All and Cols" begin
 
-    @test DataAPI.All().cols == ()
-    @test DataAPI.All(1).cols == (1,)
-    @test DataAPI.All([1,2,3], :a).cols == ([1, 2, 3], :a)
+    for v in (DataAPI.All, DataAPI.Cols)
+        @test v().cols == ()
+        @test v(1).cols == (1,)
+        @test v([1,2,3], :a).cols == ([1, 2, 3], :a)
 
-    a = DataAPI.All(DataAPI.All())
-    @test length(a.cols) == 1
-    @test a.cols[1] isa DataAPI.All
-    @test a.cols[1].cols == ()
+        a = v(v())
+        @test length(a.cols) == 1
+        @test a.cols[1] isa v
+        @test a.cols[1].cols == ()
+    end
 
 end