Change affect_neg! keyword arg to instead be a different constructor

[ChrisRackauckas]

While it seems odd to get rid of ! on a mutating function, @ccontrer 's example brings up a big issue:

callback = ContinuousCallback(condtion,affect_bounce!,rootfind,save_positions,affect_neg! = affect_negative!)

That works.

callback = ContinuousCallback(condtion,affect_bounce!,rootfind,save_positions,affect_neg!=affect_negative!)

That errors. See the difference? Julia parses affect_neg!=affect_negative! as affect_neg != affect_negative!, and errors. That's not nice behavior, and so I think it might be best to just take off the !.

[ccontrer]

Right! I thought about that. Well, it's only a keyword, isn't it? The function itself will still be mutating function.

[ChrisRackauckas]

Yeah, but the name should probably be consistent. If the keyword arg is affect_neg, then I think the field should be too, and then I think affect should be the other. They would still be mutating. Is that sensible?

[ccontrer]

If the keyword arg is affect_neg, then I think the field should be too, and then I think affect should be the other.

I agree. Or not letting affect_neg! be an keyword. As in

ContinuousCallback(condition,affect!,affect_neg!,
                   rootfind,
                   save_positions;
                   interp_points=10,
                   abstol=1e-14,reltol=0)
ContinuousCallback(condition,affect!,
                   rootfind,
                   save_positions;
                   interp_points=10,
                   abstol=1e-14,reltol=0) = ContinuousCallback(condition,affect!,affect!,
                                                               rootfind,save_positions;
                                                               interp_points=10,
                                                               abstol=1e-14,reltol=0)

or something like that.

[ChrisRackauckas]

I like that suggestion a lot. I think that's the correct way forward.

[ChrisRackauckas]

I implemented this suggestion. There is a depwarn telling people to look at the docs if they use the kwarg, and the docs are being updated right now. I'll tag a new version with this soon.