Correctly handle functors when auto-generating column names (#2934)

src/other/utils.jl

@@ -120,8 +120,13 @@ function gennames(n::Integer)
 end
 
 function funname(f)
-    n = nameof(f)
-    String(n)[1] == '#' ? :function : n
+    if applicable(nameof, f)
+        n = nameof(f)
+        return String(n)[1] == '#' ? :function : n
+    else
+        # handle the case of functors that do not support nameof
+        return :function
+    end
 end
 
 funname(c::ComposedFunction) = Symbol(funname(c.outer), :_, funname(c.inner))

test/select.jl

@@ -2346,4 +2346,18 @@ end
     @test_throws ArgumentError DataFrames.broadcast_pair(df, 1:3 .=> sum .=> Between(:x1, :x2))
 end
 
+struct Identity
+end
+
+function (::Identity)(x)
+    return x
+end
+
+@testset "correct handling of functors" begin
+    i = Identity()
+    df = DataFrame(x=1:3)
+    @test_throws ArgumentError combine(df, :x => i) # i is not Callable
+    @test combine(df, :x => identity∘i) == DataFrame(x_identity_function=1:3)
+end
+
 end # module