Merge pull request #181 from JuliaDiff/mz/struct-to-vec

try to handle structs with custom constructors

Author: mzgubic

Project.toml

@@ -1,6 +1,6 @@
 name = "FiniteDifferences"
 uuid = "26cc04aa-876d-5657-8c51-4c34ba976000"
-version = "0.12.14"
+version = "0.12.15"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/to_vec.jl

@@ -21,6 +21,18 @@ end
 # Base case -- if x is already a Vector{<:Real} there's no conversion necessary.
 to_vec(x::Vector{<:Real}) = (x, identity)
 
+# get around the constructors and make the type directly
+# Note this is moderately evil accessing julia's internals
+if VERSION >= v"1.3"
+    @generated function _force_construct(T, args...)
+        return Expr(:splatnew, :T, :args)
+    end
+else
+    @generated function _force_construct(T, args...)
+        return Expr(:new, :T, Any[:(args[$i]) for i in 1:length(args)]...)
+    end
+end
+
 # Fallback method for `to_vec`. Won't always do what you wanted, but should be fine a decent
 # chunk of the time.
 function to_vec(x::T) where {T}
@@ -35,7 +47,11 @@ function to_vec(x::T) where {T}
     function structtype_from_vec(v::Vector{<:Real})
         val_vecs = vals_from_vec(v)
         values = map((b, v) -> b(v), backs, val_vecs)
-        return T(values...)
+        try
+            T(values...)
+        catch MethodError
+            return _force_construct(T, values...)
+        end
     end
     return v, structtype_from_vec
 end

test/to_vec.jl

@@ -44,6 +44,18 @@ end
 Base.size(a::WrapperArray) = size(a.data)
 Base.getindex(a::WrapperArray, inds...) = getindex(a.data, inds...)
 
+# can not construct it from: cca = CustomConstructorArray(rand(2, 2))
+# T = typeof(cca) # CustomConstructorArray{Float64, 2, Matrix{Float64}}
+# T(rand(2, 3)) # errors
+struct CustomConstructorArray{T, N, A<:AbstractArray{T, N}} <: AbstractArray{T, N}
+    data::A
+    function CustomConstructorArray(data::A) where {T, N, A<:AbstractArray{T, N}}
+        return new{T, N, A}(data)
+    end
+end
+Base.size(a::CustomConstructorArray) = size(a.data)
+Base.getindex(a::CustomConstructorArray, inds...) = getindex(a.data, inds...)
+
 function test_to_vec(x::T; check_inferred=true) where {T}
     check_inferred && @inferred to_vec(x)
     x_vec, back = to_vec(x)
@@ -195,4 +207,9 @@ end
         wa = WrapperArray(rand(4, 5))
         test_to_vec(wa; check_inferred=false)
     end
+
+    @testset "CustomConstructorArray" begin
+        cca = CustomConstructorArray(rand(2, 3))
+        test_to_vec(cca; check_inferred=false)
+    end
 end