About MC for managing the image

[Daniel Vainsencher]

So this is what I'm working on -
MCConfigurations, by using merge instead of load when it is needed, 
solve the "older dependency problem" (at least in the context of 
developers).

However to me the fact that they specify a load order, instead of 
loading all those versions simultaneously, looks like a bug. The way 
I've been thinking about ordering issues is that if you need to specify 
an order because of reference dependencies, that's what simultaneous 
loading is for. If you need to specify an order for bootstrapping 
reasons, then you should have a sequence of configurations that each 
specify a step that works from the previous step, and allow those steps 
to define the necessary orderings of changes.

So unless there's another reason for the total order, or a problem with 
one of the above, it seems we can avoid specifying and maintaining a 
load order, and also be able to load circularly dependent packages.

Of course circularly dependent packages should be eventually dealt with, 
but that should not determine our upgrade mechanism, especially when MC 
already handles simu-load.

So I'm proposing to have MCConfigs to use simu-load for users and 
simu-merge developers, and ignore any specified order. Avi and have 
sketched the needed changes out, I'll work on it soon.

Daniel

Andreas Raab wrote:
> Early on we looked at using dependencies but they didn't work very well 
> for what we wanted to do. Most importantly, if you have a newer version 
> of a package it will load the older version instead (VERY bad). There 
> were also some serious issues with nested dependencies (Bert and I had a 
> lot of fun figuring that out). And keep in mind that dependencies are 
> not as good as a load-order since they typically only specify a partial 
>  relation (A dependsOn: X and B dependsOn: X does not specify whether A 
> is loaded before B or vice versa) whereas we wanted to make sure that 
> the updating process uses a single well-defined load order for everyone.
> 
> Cheers,
>   - Andreas
>