fix type stability of kwarg handling

src/implementation.jl

@@ -6,19 +6,16 @@ using ThreadsBasics: chunks, @spawn
 using Base: @propagate_inbounds
 using Base.Threads: nthreads, @threads
 
-
-struct NoInit end
-
 function tmapreduce(f, op, A;
-                    init=NoInit(),
                     nchunks::Int = 2 * nthreads(),
                     split::Symbol = :batch,
                     schedule::Symbol =:dynamic,
-                    outputtype::Type = Any,)
+                    outputtype::Type = Any,
+                    kwargs...)
     if schedule === :dynamic
-        _tmapreduce(f, op, A, outputtype, init, nchunks, split)
+        _tmapreduce(f, op, A, outputtype, nchunks, split; kwargs...)
     elseif schedule === :static
-        _tmapreduce_static(f, op, outputtype, A, init, nchunks, split)
+        _tmapreduce_static(f, op, outputtype, A, nchunks, split; kwargs...)
     else
         schedule_err(schedule)
     end
@@ -27,24 +24,14 @@ end
 
 treducemap(op, f, A; kwargs...) = tmapreduce(f, op, A; kwargs...)
 
-function _tmapreduce(f, op, A, ::Type{OutputType}, init, nchunks, split=:batch)::OutputType where {OutputType}
-    if init isa NoInit
-        kwargs = (;)
-    else
-        kwargs = (;init)
-    end
+function _tmapreduce(f, op, A, ::Type{OutputType}, nchunks, split=:batch; kwargs...)::OutputType where {OutputType}
     tasks = map(chunks(A; n=nchunks, split)) do inds
         @spawn mapreduce(f, op, @view(A[inds]); kwargs...)
     end
     mapreduce(fetch, op, tasks)
 end
 
-function _tmapreduce_static(f, op, ::Type{OutputType}, A, init, nchunks, split) where {OutputType}
-    if init isa NoInit
-        kwargs = (;)
-    else
-        kwargs = (;init)
-    end
+function _tmapreduce_static(f, op, ::Type{OutputType}, A, nchunks, split; kwargs...) where {OutputType}
     results = Vector{OutputType}(undef, min(nchunks, length(A)))
     @threads :static for (ichunk, inds) ∈ enumerate(chunks(A; n=nchunks, split))
         results[ichunk] = mapreduce(f, op, @view(A[inds]); kwargs...)