Use promotion rather than typejoin to infer map/broadcast output eltype

This allows `Union`s as the output type for mixtures of `Null` and
numeric types, which can be more efficient than the `Any` you'd get from
typejoin, at least in 0.7.

It also makes `SVectors` of abstract types like `Number` become concrete
after numerical operations, which is inconsistent with base, but
probably not a problem for realisitc uses of this package.

src/broadcast.jl

@@ -105,7 +105,7 @@ end
     return quote
         @_inline_meta
         elements = tuple($(exprs...))
-        @inbounds return similar_type($first_staticarray, eltype(elements), Size($newsize))(elements)
+        @inbounds return similar_type($first_staticarray, promote_tuple_eltype(elements), Size($newsize))(elements)
     end
 end
 

src/mapreduce.jl

@@ -25,7 +25,7 @@ end
     return quote
         @_inline_meta
         elements = tuple($(exprs...))
-        @inbounds return similar_type(typeof(_first(a...)), eltype(elements), Size(S))(elements)
+        @inbounds return similar_type(typeof(_first(a...)), promote_tuple_eltype(elements), Size(S))(elements)
     end
 end
 
@@ -126,7 +126,7 @@ end
     return quote
         @_inline_meta
         elements = tuple($(exprs...))
-        @inbounds return similar_type(a, eltype(elements), Size($Snew))(elements)
+        @inbounds return similar_type(a, promote_tuple_eltype(elements), Size($Snew))(elements)
     end
 end
 

test/broadcast.jl

@@ -134,16 +134,16 @@ end
     @testset "eltype after broadcast" begin
         # test cases issue #198
         let a = SVector{4, Number}(2, 2.0, 4//2, 2+0im)
-            @test eltype(a + 2) == Number
-            @test eltype(a - 2) == Number
-            @test eltype(a * 2) == Number
-            @test eltype(a / 2) == Number
+            @test_broken eltype(a + 2) == Number
+            @test_broken eltype(a - 2) == Number
+            @test_broken eltype(a * 2) == Number
+            @test_broken eltype(a / 2) == Number
         end
         let a = SVector{3, Real}(2, 2.0, 4//2)
-            @test eltype(a + 2) == Real
-            @test eltype(a - 2) == Real
-            @test eltype(a * 2) == Real
-            @test eltype(a / 2) == Real
+            @test_broken eltype(a + 2) == Real
+            @test_broken eltype(a - 2) == Real
+            @test_broken eltype(a * 2) == Real
+            @test_broken eltype(a / 2) == Real
         end
         let a = SVector{3, Real}(2, 2.0, 4//2)
             @test eltype(a + 2.0) == Float64