Add into(T, xf, foldable)

src/Transducers.jl

@@ -6,15 +6,15 @@ export Transducer, Map, Filter, Cat, MapCat, Take, PartitionBy, Scan, Zip,
     TakeLast, FlagFirst, MapSplat, ScanEmit, Enumerate, NotA, OfType,
     transduce, eduction, setinput, Reduced, reduced, unreduced, ifunreduced,
     Completing, OnInit, CopyInit, right, reducingfunction, dreduce, dtransduce,
-    withprogress, AdHocFoldable
+    withprogress, AdHocFoldable, into
 
 # Deprecated:
 export Distinct
 
 using Base.Broadcast: Broadcasted
 
 using ArgCheck
-using BangBang: BangBang, empty!!, push!!, setindex!!
+using BangBang: BangBang, Empty, empty!!, push!!, setindex!!
 using Distributed: Distributed, @everywhere
 using Logging: LogLevel, @logmsg
 using Requires

src/processes.jl

@@ -590,6 +590,18 @@ function Base.collect(xf::Transducer, coll)
 end
 # Base.collect(xf, coll) = append!([], xf, coll)
 
+"""
+    into(T, xf, foldable) :: Union{T, Nothing}
+"""
+function into(::Type{T}, xf::Transducer, coll) where T
+    rf = Reduction(xf, Completing(push!!))
+    result = unreduced(transduce(rf, Empty(T), coll))
+    if result isa Empty
+        return nothing
+    end
+    return result
+end
+
 """
     map!(xf::Transducer, dest, src; simd)