Add a value-version of of_eltyp

Especially in anonymous functions, value-arguments are easier to keep type-stable than types-as-arguments

Author: timholy

src/MappedArrays.jl

@@ -38,11 +38,13 @@ end
 
 """
     of_eltype(T, A)
+    of_eltype(val::T, A)
 
 creates a view of `A` that lazily-converts the element type to `T`.
 """
 of_eltype{S,T}(::Type{T}, data::AbstractArray{S}) = mappedarray((x->convert(T,x), y->convert(S,y)), data)
 of_eltype{T}(::Type{T}, data::AbstractArray{T}) = data
+of_eltype{S,T}(::T, data::AbstractArray{S}) = of_eltype(T, data)
 
 Base.parent(A::AbstractMappedArray) = A.data
 Base.size(A::AbstractMappedArray) = size(A.data)

test/runtests.jl

@@ -48,8 +48,12 @@ b[2,1] = 10/255
 a = [0.1 0.3; 0.2 0.4]
 b = @inferred(of_eltype(UFixed8, a))
 @test b[1,1] === UFixed8(0.1)
+b = @inferred(of_eltype(zero(UFixed8), a))
+@test b[1,1] === UFixed8(0.1)
 b[2,1] = UFixed8(0.5)
 @test a[2,1] == UFixed8(0.5)
 @test !(b === a)
-b = of_eltype(Float64, a)
+b = @inferred(of_eltype(Float64, a))
+@test b === a
+b = @inferred(of_eltype(0.0, a))
 @test b === a