Slight refactor to collection widening

base/array.jl

@@ -656,6 +656,15 @@ function collect_to_with_first!(dest, v1, itr, st)
     return grow_to!(dest, itr, st)
 end
 
+function setindex_widen!(dest::Array{T}, el, i) where T
+    @_inline_meta
+    R = promote_typejoin(T, typeof(el))
+    new = similar(dest, R)
+    copyto!(new,1, dest,1, i-1)
+    @inbounds new[i] = el
+    return new
+end
+
 function collect_to!(dest::AbstractArray{T}, itr, offs, st) where T
     # collect to dest array, checking the type of each result. if a result does not
     # match, widen the result type and re-dispatch.
@@ -668,10 +677,7 @@ function collect_to!(dest::AbstractArray{T}, itr, offs, st) where T
             @inbounds dest[i] = el::T
             i += 1
         else
-            R = promote_typejoin(T, typeof(el))
-            new = similar(dest, R)
-            copyto!(new,1, dest,1, i-1)
-            @inbounds new[i] = el
+            new = setindex_widen!(dest, el, i)
             return collect_to!(new, itr, i+1, st)
         end
     end
@@ -686,6 +692,21 @@ function grow_to!(dest, itr)
     grow_to!(dest2, itr, y[2])
 end
 
+function push_widen!(dest, el)
+    @_inline_meta
+    T = eltype(dest)
+    S = typeof(el)
+    new = sizehint!(empty(dest, promote_typejoin(T, S)), length(dest))
+    if new isa AbstractSet
+        # TODO: merge back these two branches when copy! is re-enabled for sets/vectors
+        union!(new, dest)
+    else
+        append!(new, dest)
+    end
+    push!(new, el)
+    return new
+end
+
 function grow_to!(dest, itr, st)
     T = eltype(dest)
     y = iterate(itr, st)
@@ -695,14 +716,7 @@ function grow_to!(dest, itr, st)
         if S === T || S <: T
             push!(dest, el::T)
         else
-            new = sizehint!(empty(dest, promote_typejoin(T, S)), length(dest))
-            if new isa AbstractSet
-                # TODO: merge back these two branches when copy! is re-enabled for sets/vectors
-                union!(new, dest)
-            else
-                append!(new, dest)
-            end
-            push!(new, el)
+            new = push_widen!(dest, el)
             return grow_to!(new, itr, st)
         end
         y = iterate(itr, st)