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7324 :: C++ bindings - doubt with an argument's default value

• mantielero (orginal) [2021-01-02T20:54:46+01:00] view original

  I have doubts with the following header: Material from OpenSceneGraph:

  namespace osg {
  /** Material - encapsulates OpenGL glMaterial state.*/
  class OSG_EXPORT Material : public StateAttribute
  {
      public :
          
          Material();
          
          /** Copy constructor using CopyOp to manage deep vs shallow copy. */
          Material(const Material& mat,const CopyOp& copyop=CopyOp::SHALLOW_COPY):
  Run

  in particular the const CopyOp& copyop=CopyOp::SHALLOW_COPY) part.

  I am converting that constructor into this:

  proc constructMaterial*(mat: Material, copyop: CopyOp = SHALLOW_COPY): Material {.constructor,importcpp: "osg::Material::Material(@)".}
  Run

  The problem comes with SHALLOW_COPY which is an enum (Options) defined here. This is the default value for copyop whose type is CopyOp which is an object.

  This creates a type mismatch error:

  
  /home/jose/src/openscenegraph.nim/osg/Material.nim(30, 57) Error: type mismatch: got <Options> but expected 'CopyOp = object'
  Run

  Any suggestion about how to handle this defaut value?

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• haxscramper_ (orginal) [2021-01-02T21:07:07+01:00] view original

  It seems like Options is implicitly convertible to CopyOp on C++ side, but this is not the case in nim. In general, C++ default arguments should be wrapped using arg: Type = initType(defaultValue) where toType is wrapper for implicit conversion constructor on the C++ side.

  In C++ default arguments are constructor parameters and not actual values to be used (that's why it is posssible to use aggregate initalization in default parameters for example).

  This is a much more convoluted example for wrapping different combinations of default parameters -

  • https://github.com/haxscramper/hax-nim/blob/master/wraptests/initalization/init.nim
  • https://github.com/haxscramper/hax-nim/blob/master/wraptests/initalization/header.hpp

  With generic argument

  • https://github.com/haxscramper/hax-nim/blob/master/wraptests/default_generics/generics.nim
  • https://github.com/haxscramper/hax-nim/blob/master/wraptests/default_generics/generics.hpp

  In C++ default arguments are

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• mantielero (orginal) [2021-01-02T22:41:46+01:00] view original

  Thanks. Understood. It looks I have to do:

  proc constructMaterial*(mat: Material, copyop: CopyOp = constructCopyOp(CopyFlags(SHALLOW_COPY))): Material {.constructor,importcpp: "osg::Material::Material(@)".}    ## Copy constructor using CopyOp to manage deep vs shallow copy.
  Run

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