Promote returned values to a common type in replace()

src/Nulls.jl

@@ -121,6 +121,8 @@ xor(::Integer, ::Null) = null
 
 Return an iterator wrapping iterable `itr` which replaces [`null`](@ref) values with
 `replacement`. When applicable, the size of `itr` is preserved.
+If the type of `replacement` differs from the element type of `itr`,
+returned values are promoted to a common type.
 
 See also: [`Nulls.skip`](@ref), [`Nulls.fail`](@ref)
 
@@ -132,14 +134,23 @@ julia> collect(Nulls.replace([1, null, 2], 0))
  0
  2
 
+ julia> collect(Nulls.replace([1, null, 2], 0.0))
+ 3-element Array{Float64,1}:
+  1.0
+  0.0
+  2.0
+
 julia> collect(Nulls.replace([1 null; 2 null], 0))
 2×2 Array{Int64,2}:
  1  0
  2  0
 
 ```
 """
-replace(itr, replacement) = EachReplaceNull(itr, replacement)
+function replace(itr, replacement)
+    U = promote_type(eltype(itr), typeof(replacement))
+    EachReplaceNull(itr, convert(U, replacement))
+end
 struct EachReplaceNull{T, U}
     x::T
     replacement::U
@@ -152,11 +163,12 @@ Base.length(itr::EachReplaceNull) = length(itr.x)
 Base.size(itr::EachReplaceNull) = size(itr.x)
 Base.start(itr::EachReplaceNull) = start(itr.x)
 Base.done(itr::EachReplaceNull, state) = done(itr.x, state)
-Base.eltype(itr::EachReplaceNull) =
-    Union{Nulls.T(eltype(itr.x)), typeof(itr.replacement)}
+Base.eltype(itr::EachReplaceNull{T, U}) where {T, U} =
+    promote_type(Nulls.T(eltype(itr.x)), U)
 @inline function Base.next(itr::EachReplaceNull, state)
     v, s = next(itr.x, state)
-    ((isnull(v) ? itr.replacement : v)::eltype(itr), s)
+    el = convert(eltype(itr), isnull(v) ? itr.replacement : v)
+    (el::eltype(itr), s)
 end
 
 """

test/runtests.jl

@@ -129,6 +129,12 @@ using Base.Test, Nulls
     @test size(x) == (4,)
     @test collect(x) == collect(1:4)
     @test collect(x) isa Vector{Int}
+    x = Nulls.replace([1, 2, null, 4], 3.0)
+    @test eltype(x) === Float64
+    @test length(x) == 4
+    @test size(x) == (4,)
+    @test collect(x) == collect(1:4)
+    @test collect(x) isa Vector{Float64}
     x = Nulls.replace([1 2; null 4], 3)
     @test eltype(x) === Int
     @test length(x) == 4