Merge pull request #83 from JuliaDiff/ox/nongenbacking

Bring back nongenerated backing

Author: oxinabox

src/compat.jl

@@ -1,3 +1,23 @@
 if VERSION < v"1.2"
     Base.getproperty(x::Tuple, f::Int) = getfield(x, f)
 end
+
+if VERSION < v"1.1"
+    # Note: these are actually *better* than the ones in julia 1.1, 1.2, 1.3,and 1.4
+    # See: https://github.com/JuliaLang/julia/issues/34292
+    function fieldtypes(::Type{T}) where T
+        if @generated
+            ntuple(i -> fieldtype(T, i), fieldcount(T))
+        else
+            ntuple(i -> fieldtype(T, i), fieldcount(T))
+        end
+    end
+
+    function fieldnames(::Type{T}) where T
+        if @generated
+            ntuple(i -> fieldname(T, i), fieldcount(T))
+        else
+            ntuple(i -> fieldname(T, i), fieldcount(T))
+        end
+    end
+end

src/differentials/composite.jl

@@ -77,14 +77,27 @@ backing(x::Tuple) = x
 backing(x::NamedTuple) = x
 backing(x::Composite) = getfield(x, :backing)
 
-@generated function backing(x)::NamedTuple
-    !isstructtype(x) && throw(DomainError(x, "backing can only be use on composite types"))
-    nfields = fieldcount(x)
-    names = ntuple(ii->fieldname(x, ii), nfields)
-    types = ntuple(ii->fieldtype(x, ii), nfields)
-
-    vals = Expr(:tuple, ntuple(ii->:(getfield(x, $ii)), nfields)...)
-    return :(NamedTuple{$names, Tuple{$(types...)}}($vals))
+function backing(x::T)::NamedTuple where T
+    # note: all computation outside the if @generated happens at runtime.
+    # so the first 4 lines of the branchs look the same, but can not be moved out.
+    # see https://github.com/JuliaLang/julia/issues/34283
+    if @generated
+        !isstructtype(T) && throw(DomainError(T, "backing can only be use on composite types"))
+        nfields = fieldcount(T)
+        names = fieldnames(T)
+        types = fieldtypes(T)
+        
+        vals = Expr(:tuple, ntuple(ii->:(getfield(x, $ii)), nfields)...)
+        return :(NamedTuple{$names, Tuple{$(types...)}}($vals))
+    else
+        !isstructtype(T) && throw(DomainError(T, "backing can only be use on composite types"))
+        nfields = fieldcount(T)
+        names = fieldnames(T)
+        types = fieldtypes(T)
+
+        vals = ntuple(ii->getfield(x, ii), nfields)
+        return NamedTuple{names, Tuple{types...}}(vals)
+    end
 end
 
 """