add adapt_structure macro (#38)

* add adapt_structure macro

* add tests

* clarify doc

* move struct outside of testset for old scope rules

src/Adapt.jl

@@ -43,6 +43,7 @@ adapt_structure(to, x) = adapt_storage(to, x)
 adapt_storage(to, x) = x
 
 include("base.jl")
+include("macro.jl")
 include("wrappers.jl")
 
 end # module

src/macro.jl

@@ -0,0 +1,14 @@
+"""
+    Adapt.@adapt_structure T
+
+Define a method `adapt_structure(to, obj::T)` which calls `adapt_structure` on each field
+of `obj` and constructs a new instance of `T` using the default constuctor `T(...)`.
+"""
+macro adapt_structure(T)
+    names = fieldnames(Core.eval(__module__, T))
+    quote
+        function Adapt.adapt_structure(to, obj::$(esc(T)))
+            $(esc(T))($([:(Adapt.adapt_structure(to, obj.$name)) for name in names]...))
+        end
+    end    
+end

test/runtests.jl

@@ -168,3 +168,21 @@ end
     @test Adapt.parent(LinearAlgebra.Transpose{Float64,Array{Float64,1}}) == Array
     @test Adapt.parent(Adapt.WrappedSubArray{Float64,3,Array{Float64,3}}) == Array
 end
+
+
+struct MyStruct{A,B}
+    a::A
+    b::B
+end
+
+@testset "@adapt_structure" begin
+
+    Adapt.@adapt_structure MyStruct
+
+    u = ones(3)
+    v = zeros(5)
+
+    @test_adapt CustomArray MyStruct(u,v) MyStruct(CustomArray(u), CustomArray(v))
+    @test_adapt CustomArray MyStruct(u,1.0) MyStruct(CustomArray(u), 1.0)
+
+end