Merge pull request #74 from nickrobinson251/npr/73-rational-promotion

Fix promotion between FixedDecimal and Rational

Author: NHDaly

src/FixedPointDecimals.jl

@@ -328,7 +328,7 @@ end
 
 Base.promote_rule(::Type{FD{T, f}}, ::Type{<:Integer}) where {T, f} = FD{T, f}
 Base.promote_rule(::Type{<:FD}, ::Type{TF}) where {TF <: AbstractFloat} = TF
-Base.promote_rule(::Type{<:FD}, ::Type{Rational{TR}}) where {TR} = Rational{TR}
+Base.promote_rule(::Type{<:FD{T}}, ::Type{Rational{TR}}) where {T, TR} = Rational{promote_type(T, TR)}
 
 # TODO: decide if these are the right semantics;
 # right now we pick the bigger int type and the bigger decimal point

test/runtests.jl

@@ -266,6 +266,12 @@ end
     @test 1 + FD2(0.1) === FD2(1.1)
     @test FD2(0.1) + FD4(0.0001) === FD4(0.1001)
     @test WFD2(0.1) + FD4(0.0001) === WFD4(0.1001)
+
+    # promotion with Rational
+    # see https://github.com/JuliaMath/FixedPointDecimals.jl/issues/73
+    r = Rational{Int8}(1//1)
+    fd = FixedDecimal{Int128,4}(2.5806)
+    @test (r + fd) isa Rational{Int128}
 end
 
 @testset "float" begin