Generalize at-argout to multiple arguments.

src/utils.jl

@@ -93,33 +93,41 @@ A common use case is to pass a newly-created Ref and immediately dereference tha
 
     @argout(some_getter(Ref{Int}()))[]
 
+If no output argument is specified, `nothing` will be returned.
+Multiple output arguments return a tuple.
+
 """
 macro argout(ex)
     Meta.isexpr(ex, :call) || throw(ArgumentError("@argout macro should be applied to a function call"))
 
-    # look for an output argument (`out(...)`)
-    output_arg = 0
+    block = quote end
+
+    # look for output arguments (`out(...)`)
+    output_vars = []
     args = ex.args[2:end]
     for (i,arg) in enumerate(args)
         if Meta.isexpr(arg, :call) && arg.args[1] == :out
-            output_arg == 0 || throw(ArgumentError("There can only be one output argument (both argument $output_arg and $i are marked out)"))
-            output_arg = i
+            # allocate a variable
+            @gensym output_val
+            push!(block.args, :($output_val = $(ex.args[i+1].args[2]))) # strip `output(...)`
+            push!(output_vars, output_val)
+
+            # replace the argument
+            ex.args[i+1] = output_val
         end
     end
-    output_arg == 0 && throw(ArgumentError("No output argument found"))
-
-    # get the arguments
-    Largs = ex.args[2:output_arg]
-    ret_arg = ex.args[output_arg+1].args[2] # strip the call to `out`
-    Rargs = ex.args[output_arg+2:end]
-
-    @gensym ret_val
-    ex.args[output_arg+1] = ret_val
-    esc(quote
-        $ret_val = $ret_arg
-        $ex
-        $ret_val
-    end)
+
+    # generate a return
+    push!(block.args, ex)
+    if isempty(output_vars)
+        push!(block.args, :(nothing))
+    elseif length(output_vars) == 1
+        push!(block.args, :($(output_vars[1])))
+    else
+        push!(block.args, :(tuple($(output_vars...))))
+    end
+
+    esc(block)
 end
 
 """

test/base.jl

@@ -6,6 +6,16 @@ import CUDAdrv: CuPtr, CU_NULL
 
 @test CuArrays.functional()
 
+@testset "essential utilities" begin
+  f() = 1
+  f(a) = 2
+  f(a,b) = 3
+
+  @test CuArrays.@argout(f()) == nothing
+  @test CuArrays.@argout(f(out(4))) == 4
+  @test CuArrays.@argout(f(out(5), out(6))) == (5,6)
+end
+
 @testset "Memory" begin
   CuArrays.alloc(0)