From 8251cb3f9558671fddea913b415f6becbf2bd9e0 Mon Sep 17 00:00:00 2001
From: Adrian Hill <adrian.hill@mailbox.org>
Date: Thu, 15 Aug 2024 13:56:41 +0200
Subject: [PATCH] Add direct type conversions on `Dual` (#168)

---
 src/overloads/conversion.jl |  8 ++++++++
 src/patterns.jl             |  4 ++--
 test/test_constructors.jl   | 30 ++++++++++++++++++++++++++++--
 test/test_hessian.jl        |  7 ++++++-
 4 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/src/overloads/conversion.jl b/src/overloads/conversion.jl
index 91f4dd3..ceff378 100644
--- a/src/overloads/conversion.jl
+++ b/src/overloads/conversion.jl
@@ -50,6 +50,14 @@ function Base.convert(::Type{Dual{P1,T}}, d::Dual{P2,T}) where {P1,P2,T}
     return Dual(convert(P1, primal(d)), tracer(d))
 end
 
+# Explicit type conversions
+for T in (:Int, :Integer, :Float64, :Float32)
+    @eval function Base.$T(d::Dual)
+        isemptytracer(d) || throw(InexactError(Symbol($T), $T, d))
+        $T(primal(d))
+    end
+end
+
 ## Constants
 # These are methods defined on types. Methods on variables are in operators.jl 
 Base.zero(::Type{D})        where {P,T,D<:Dual{P,T}} = D(zero(P),        myempty(T))
diff --git a/src/patterns.jl b/src/patterns.jl
index c79da1a..a07756a 100644
--- a/src/patterns.jl
+++ b/src/patterns.jl
@@ -143,9 +143,9 @@ function union_product!(
     return hessian
 end
 
-#=======================#
+#=========================#
 # AbstractGradientPattern #
-#=======================#
+#=========================#
 
 # For use with GradientTracer.
 
diff --git a/test/test_constructors.jl b/test/test_constructors.jl
index cc8b906..fca3eff 100644
--- a/test/test_constructors.jl
+++ b/test/test_constructors.jl
@@ -1,7 +1,7 @@
 # Test construction and conversions of internal tracer types
 using SparseConnectivityTracer: AbstractTracer, GradientTracer, HessianTracer, Dual
-using SparseConnectivityTracer: primal, tracer, isemptytracer
-using SparseConnectivityTracer: myempty, name
+using SparseConnectivityTracer: primal, tracer, isemptytracer, myempty, name
+using SparseConnectivityTracer: IndexSetGradientPattern
 using Test
 
 # Load definitions of GRADIENT_TRACERS, GRADIENT_PATTERNS, HESSIAN_TRACERS and HESSIAN_PATTERNS
@@ -200,3 +200,29 @@ end
         test_similar(T)
     end
 end
+
+@testset "Explicit type conversions on Dual" begin
+    @testset "$T" for T in union(GRADIENT_TRACERS, HESSIAN_TRACERS)
+        P = IndexSetGradientPattern{Int,BitSet}
+        T = GradientTracer{P}
+
+        p       = P(BitSet(2))
+        t_full  = T(p)
+        t_empty = myempty(T)
+        d_full  = Dual(1.0, t_full)
+        d_empty = Dual(1.0, t_empty)
+
+        @testset "Non-empty tracer" begin
+            @testset "$TOUT" for TOUT in (Int, Integer, Float64, Float32)
+                @test_throws InexactError TOUT(d_full)
+            end
+        end
+        @testset "Empty tracer" begin
+            @testset "$TOUT" for TOUT in (Int, Integer, Float64, Float32)
+                out = TOUT(d_empty)
+                @test out isa TOUT # not a Dual!
+                @test isone(out)
+            end
+        end
+    end
+end
diff --git a/test/test_hessian.jl b/test/test_hessian.jl
index 2466571..9fb0d5d 100644
--- a/test/test_hessian.jl
+++ b/test/test_hessian.jl
@@ -9,12 +9,17 @@ using NNlib: NNlib
 
 # Load definitions of GRADIENT_TRACERS, GRADIENT_PATTERNS, HESSIAN_TRACERS and HESSIAN_PATTERNS
 include("tracers_definitions.jl")
+REAL_TYPES = (Float64, Int, Bool, UInt8, Float16, Rational{Int})
 
-# This exists to be able to quickly run tests in the REPL.
+# These exists to be able to quickly run tests in the REPL.
 # NOTE: H gets overwritten inside the testsets.
 method = TracerSparsityDetector()
 H(f, x) = hessian_sparsity(f, x, method)
 
+P = first(HESSIAN_PATTERNS)
+T = HessianTracer{P}
+D = Dual{Int,T}
+
 @testset "Global Hessian" begin
     @testset "$P" for P in HESSIAN_PATTERNS
         T = HessianTracer{P}