Default constructor could take instance as first argument

[lawremi]

methods::initialize() takes an instance of the class (or subclass, in which case extra slots are dropped) as the first argument, and named arguments specify the slot values, overriding those of the first argument. This behavior has proven convenient for creating derivative objects. I wonder if the default constructor could behave similarly. This would often force property arguments to be named in calls to the constructor, but that at least benefits clarity.

I wonder though whether this is a feature that most benefits implementations, and so should instead be supported by a different function, like set_props(), which would just be a simple wrapper around props<-().

[hadley]

You can do this currently with `props<-`(obj, x = 1, y = 2) but that's an unpleasant syntax.

[hadley]

@lawremi Which of the following syntaxes would you prefer?

set_props(obj, x = 1, y = 2)
set_props(obj, list(x = 1, y = 2))

The first is more user friendly but there's no obvious way to supply a list.

In the tidyverse we'd use "dynamic dots" here, so you could do set_props(obj, !!!a_list). I'm not sure what the base equivalent is? Add a .list argument so you can do set_props(obj, .list = a_list)?

[mmaechler]

Hmm, I never got why set_props() was needed when we have props(obj) <- <propslist>
and indeed the RHS could be a simple list ??
Using set_*() is really "S4-ish" and "non-R-ish" in comparison with props(.) <- ..
{yes, I must have missed something}

[hadley]

@mmaechler sometimes you want to create a modified copy of the object, rather than modifying in place.