From b4188c83155bbde70f081617c6edc654738b98d6 Mon Sep 17 00:00:00 2001
From: Chris Foster <chris42f@gmail.com>
Date: Fri, 17 Apr 2020 16:50:50 +1000
Subject: [PATCH] Widening-based map() to remove return_type

---
 src/mapreduce.jl | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/src/mapreduce.jl b/src/mapreduce.jl
index 890fb24..b5537d4 100644
--- a/src/mapreduce.jl
+++ b/src/mapreduce.jl
@@ -1,8 +1,32 @@
 function Base.map(f, a::StaticArrayLite)
-    T = Core.Compiler.return_type(f, Tuple{eltype(a)})
-    out = similar(a, T, size(a))
-    map!(f, out, a)
-    return freeze(out)
+    if length(a) == 0
+        T = Core.Compiler.return_type(f, Tuple{eltype(a)})
+        return freeze(similar(a, T, size(a)))
+    end
+    @inbounds x = f(a[first(LinearIndices(a))])
+    out = similar(a, typeof(x), size(a))
+    freeze(_map_widen!(out, 0, x, f, a))
+end
+
+function _map_widen!(out, offset, x, f, a)
+    a_i1 = first(LinearIndices(a))
+    out_i1 = first(LinearIndices(out))
+    T = eltype(out)
+    while true
+        @inbounds out[out_i1+offset] = x
+        offset += 1
+        if offset >= length(a)
+            break
+        end
+        @inbounds x = f(a[a_i1+offset])
+        if !(typeof(x) === T || x isa T)
+            T2 = Base.promote_typejoin(T, typeof(x))
+            out2 = similar(a, T2, size(a))
+            copyto!(out2, out_i1, out, out_i1, offset)
+            return _map_widen!(out2, )
+        end
+    end
+    return out
 end
 
 function Base.map(f, a::StaticArrayLite, b::StaticArrayLite)
@@ -44,4 +68,4 @@ function Base.mapreduce(f, op, a::StaticArrayLite, b::StaticArrayLite; init)
         out = op(f(@inbounds(a[i]),@inbounds(b[i])), out)
     end
     return out
-end
\ No newline at end of file
+end