Re: programmatically create a TClass at runtime

Philippe,

On Wed, 4 May 2011 12:42:52 -0500, Philippe Canal <pcanal_at_fnal.gov> wrote:
> Hi Sebastien,
>
> The work need is similar to the work done by Cintex for Reflex.
> For example the answer to your direct question is somewhat
> in the file cint/cintex/src/ROOTClassEnhancer.cxx
thanks. I think "I know kung-fu now".

I actually went using/wrapping the Reflex(TypeBuilder) API as it is somewhat more straightforward than the G__stuff one (or perhaps it is b/c I am more familiar with the Reflex one ?)

probably not the most efficient use of CPU cycles but I can read/write simple structs...

so now, to tackle the Go-slices so they are properly recognized as collections, do I understand correctly that I "just" need to implement a 'createCollFuncTable' FunctionTypeBuilder with the correct 'size', 'feed', ... slots ?

I fear they won't be completely properly handled as most of the code I have seen relies on TClassEdit::IsSTLCont(typename_str) to decide if a type is collection-like...
or should I just grab the TClass corresponding to the new Reflex::Type and call TClass::SetCollectionProxy(go_slice_proxy) ?

-s

>
> Cheers,
> Philippe.
>
> On 5/4/11 12:00 PM, Sebastien Binet wrote:
> > hi there,
> >
> > I am playing with Go (the language at golang.org) and trying to see if
> > one could use ROOT as an I/O back-end.
> >
> > Go has built-in reflection capabilities so theoretically any Go struct
> > can be described at runtime/compiletime and converted to a Reflex or
> > CINT metadata.
> > Moreover, Go-struct usually have the same layout than their C cousin
> > (that's not true for Go-strings and Go-slices (which are views into
> > arrays))
> >
> > the amount of work on my side to be able to support the below kind of
> > code should be rather minimal:
> >
> > // ---
> > type MyStruct struct {
> > IntData [10]int32
> > FloatData [20]float64
> > }
> >
> > f := ROOT.NewFile("foo.root", "recreate")
> > t := ROOT.NewTree("tree", "title")
> > s := MyStruct{}
> > t.Branch("mystruct",&s) //<---
> > // ---
> >
> > From my end, I would need to create a ROOT::TClass instance for the
> > Go-struct MyStruct leveraging Go's "reflect" package which knows the types
> > and offsets of each data member.
> >
> > is this possible without reaching to automatically generated code ?
> > (rootcint|genreflex)
> > that would simplify the amount of infrastructure to provide...
> >
> > -s
> >
> > PS: right now, I am just unfolding the struct and register branches like
> > so (in pseudo-code):
> > for f := range typ.Fields() {
> > s := "mystruct_"+f.Name()
> > field_addr := obj.Address()+f.Offset()
> > branch_typ := s+"/"+go2ctype[f.Type()].Name()
> > tree.Branch(s, field_addr, branch_typ)
> > }
> >

-- 
#########################################
# Dr. Sebastien Binet
# Laboratoire de l'Accelerateur Lineaire
# Universite Paris-Sud XI
# Batiment 200
# 91898 Orsay
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