Add a ForwardDiff extension for dimensionless quantities (#765)

Author: Ickaser

Project.toml

@@ -11,16 +11,19 @@ Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 
 [weakdeps]
 ConstructionBase = "187b0558-2788-49d3-abe0-74a17ed4e7c9"
+ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 InverseFunctions = "3587e190-3f89-42d0-90ee-14403ec27112"
 
 [extensions]
 ConstructionBaseUnitfulExt = "ConstructionBase"
+ForwardDiffExt = "ForwardDiff"
 InverseFunctionsUnitfulExt = "InverseFunctions"
 
 [compat]
 Aqua = "0.8"
 ConstructionBase = "1"
 Dates = "<0.0.1, 1"
+ForwardDiff = "0.10, 1"
 InverseFunctions = "0.1"
 LinearAlgebra = "<0.0.1, 1"
 REPL = "<0.0.1, 1"
@@ -31,11 +34,12 @@ julia = "1"
 [extras]
 Aqua = "4c88cf16-eb10-579e-8560-4a9242c79595"
 ConstructionBase = "187b0558-2788-49d3-abe0-74a17ed4e7c9"
+ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 InverseFunctions = "3587e190-3f89-42d0-90ee-14403ec27112"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 REPL = "3fa0cd96-eef1-5676-8a61-b3b8758bbffb"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Aqua", "ConstructionBase", "InverseFunctions", "LinearAlgebra", "Test", "Random", "REPL"]
+test = ["Aqua", "ConstructionBase", "ForwardDiff", "InverseFunctions", "LinearAlgebra", "Test", "Random", "REPL"]

ext/ForwardDiffExt.jl

@@ -0,0 +1,9 @@
+module ForwardDiffExt
+using Unitful
+using ForwardDiff
+
+function Base.convert(d::Type{ForwardDiff.Dual{T, V, N}}, q::Quantity{T2, NoDims}) where {T, V, N, T2}
+    return d(uconvert(NoUnits, q))
+end
+
+end

test/runtests.jl

@@ -3,6 +3,7 @@ using Test, LinearAlgebra, Random, ConstructionBase, InverseFunctions
 import Unitful: DimensionError, AffineError
 import Unitful: LogScaled, LogInfo, Level, Gain, MixedUnits, Decibel
 import Unitful: FreeUnits, ContextUnits, FixedUnits, AffineUnits, AffineQuantity
+import ForwardDiff
 
 import Unitful:
     nm, μm, mm, cm, m, km, inch, ft, mi,
@@ -2206,6 +2207,12 @@ end
     @test isa(TUM.fu^2, TUM.FakeDim212345Units)
 end
 
+if isdefined(Base, :get_extension)
+    @testset "ForwardDiff extension, solving Issue 682" begin
+        @test ForwardDiff.Dual(1.0)*u"cm/m" + ForwardDiff.Dual(1.0) == 1.01
+        @test ForwardDiff.Dual(1.0)*u"cm/m" == ForwardDiff.Dual(0.01)
+    end
+end
 
 struct Num <: Real
    x::Float64