Handle empty input

CHANGELOG.md

@@ -1,6 +1,10 @@
 OhMyThreads.jl Changelog
 =========================
 
+Version 0.5.2
+-------------
+- ![Enhancement][badge-enhancement] For empty input (e.g. `Float64[]` or `11:10`) behavior is now aligned with the serial functions in `Base`.
+
 Version 0.5.1
 -------------
 - ![Feature][badge-feature] Within a parallel `@tasks` block one can now mark a region with `@one_by_one`. This region will be run by one task at a time ("critical region").

src/implementation.jl

@@ -60,13 +60,9 @@ function tmapreduce(f, op, Arrs...;
         kwargs...)
     mapreduce_kwargs = isgiven(init) ? (; init) : (;)
     _scheduler = _scheduler_from_userinput(scheduler; kwargs...)
-    if isempty(first(Arrs))
-        isempty(mapreduce_kwargs) && reduce_empty_err()
-        return mapreduce_kwargs.init
-    end
 
-    # @show _scheduler
-    if _scheduler isa SerialScheduler
+    if _scheduler isa SerialScheduler || isempty(first(Arrs))
+        # empty input collection → align with Base.mapreduce behavior
         mapreduce(f, op, Arrs...; mapreduce_kwargs...)
     else
         @noinline _tmapreduce(f, op, Arrs, outputtype, _scheduler, mapreduce_kwargs)
@@ -78,10 +74,6 @@ end
     throw(ArgumentError("Providing an explicit scheduler as well as direct keyword arguments (e.g. $(kwargstr)) is currently not supported."))
 end
 
-@noinline function reduce_empty_err()
-    throw(ArgumentError("reducing over an empty collection is not allowed; consider supplying `init`"))
-end
-
 treducemap(op, f, A...; kwargs...) = tmapreduce(f, op, A...; kwargs...)
 
 # DynamicScheduler: AbstractArray/Generic
@@ -357,7 +349,8 @@ function tmap(f,
     end
 
     Arrs = (A, _Arrs...)
-    if _scheduler isa SerialScheduler
+    if _scheduler isa SerialScheduler || isempty(A)
+        # empty input collection → align with Base.map behavior
         map(f, Arrs...; kwargs...)
     else
         check_all_have_same_indices(Arrs)

test/runtests.jl

@@ -364,14 +364,30 @@ end;
 end;
 
 @testset "empty collections" begin
+    @static if VERSION < v"1.11.0-"
+        err = MethodError
+    else
+        err = ArgumentError
+    end
     for empty_coll in (11:9, Float64[])
         for f in (sin, x -> im * x, identity)
             for op in (+, *, min)
-                @test_throws ArgumentError tmapreduce(f, op, empty_coll)
+                # mapreduce
                 for init in (0.0, 0, 0.0 * im, 0.0f0)
                     @test tmapreduce(f, op, empty_coll; init) == init
                 end
+                # foreach
                 @test tforeach(f, empty_coll) |> isnothing
+                # reduce
+                if op != min
+                    @test treduce(op, empty_coll) == reduce(op, empty_coll)
+                else
+                    @test_throws err treduce(op, empty_coll)
+                end
+                # map
+                @test tmap(f, empty_coll) == map(f, empty_coll)
+                # collect
+                @test tcollect(empty_coll) == collect(empty_coll)
             end
         end
     end