size of a glm-like object

Dear all,
I'm writing a package where the main function fn(), say, returns a glm-like
object, with three additional components.

obj<-glm(....)
out<-fn(obj,....)

out is substantially an updated version of obj, with the same response and
some (two or three) additional variables in the linear predictor.
My problem is that out is much bigger than obj, and the three additional
components don't seem responsible, as they are quite small.

class(obj)

[1] "glm" "lm"

class(out)

[1] "myclass" "glm"       "lm"

object.size(obj)

[1] 1685228

object.size(out)

[1] 2701292

Why is out so larger than obj? the additional components are rather small
and the remaining ones seem approximatevely the same.
Many thanks,
vito

#the size of the additional components:

object.size(out$psi)

[1] 348

object.size(out$it)

[1] 36

object.size(out$epsilon)

[1] 36

#the size of some remaining component:

all.equal(out$y,obj$y)

[1] TRUE

object.size(obj$R)

[1] 9284

object.size(out$R)

[1] 10356

object.size(obj$coef)

[1] 1024

object.size(out$coef)

[1] 1064

object.size(obj$call)

[1] 1456

object.size(out$call)

[1] 764


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