use Base.Fix1 instead of closures in ForwardDiffStaticArraysExt.jl (#735)

* use `Base.Fix1` instead of closures in `ForwardDiffStaticArraysExt.jl`

* inference tets from issue #639 and pr #735

Author: jondeuce

ext/ForwardDiffStaticArraysExt.jl

@@ -103,16 +103,16 @@ end
     T = typeof(Tag(f, eltype(x)))
     ydual = static_dual_eval(T, f, x)
     result = DiffResults.jacobian!(result, extract_jacobian(T, ydual, x))
-    result = DiffResults.value!(d -> value(T,d), result, ydual)
+    result = DiffResults.value!(Base.Fix1(value, T), result, ydual)
     return result
 end
 
 # Hessian
-ForwardDiff.hessian(f::F, x::StaticArray) where {F} = jacobian(y -> gradient(f, y), x)
+ForwardDiff.hessian(f::F, x::StaticArray) where {F} = jacobian(Base.Fix1(gradient, f), x)
 ForwardDiff.hessian(f::F, x::StaticArray, cfg::HessianConfig) where {F} = hessian(f, x)
 ForwardDiff.hessian(f::F, x::StaticArray, cfg::HessianConfig, ::Val) where {F} = hessian(f, x)
 
-ForwardDiff.hessian!(result::AbstractArray, f::F, x::StaticArray) where {F} = jacobian!(result, y -> gradient(f, y), x)
+ForwardDiff.hessian!(result::AbstractArray, f::F, x::StaticArray) where {F} = jacobian!(result, Base.Fix1(gradient, f), x)
 
 ForwardDiff.hessian!(result::MutableDiffResult, f::F, x::StaticArray) where {F} = hessian!(result, f, x, HessianConfig(f, result, x))
 

test/JacobianTest.jl

@@ -259,6 +259,24 @@ end
 @testset "type stability" begin
     g!(dy, y) = dy[1] = y[1]
     @inferred ForwardDiff.jacobian(g!, [1.0], [0.0])
+
+    @testset "issue 639" begin
+        f(x) = SA[x[1]^2+x[2]^2, x[2]^2+x[3]^2]
+        x = SA[1.0, 2.0, 3.0]
+        y = f(x)
+        imdr = DiffResults.JacobianResult(y, x)
+        @inferred ForwardDiff.jacobian!(imdr, f, x)
+    end
+
+    @testset "pr 735" begin
+        f(x) = x .^ 2 ./ 2
+        function withjacobian(x)
+            res = DiffResults.JacobianResult(x)
+            res = ForwardDiff.jacobian!(res, f, x)
+            return DiffResults.value(res), DiffResults.jacobian(res)
+        end
+        @inferred withjacobian(SA[1.0, 2.0])
+    end
 end
 
 end # module