Yes by design, meaning you do not have an FHS structure where "installing" means copy this in /usr/share, this in /usr/lib ... Alla packages just see a small "virtual" root tree, meaning a network of symlinks.
You can choose for package A to se package B and C, but not D, different versions means simply different packages because you have package alone, let's say the current stable version but also package_major_minor for various supported major or minor version. As well as you can choose to fetch sources from a specific commit from a public repo, build them and link them in the system.
Every package is not "isolated" in the container self, like small userlands on a common kernel, but in the sense of "having different views of the common system", so you avoid wasting gazzilion of storage and ram and CPU plus anything is still from the upstream or yourself, there are no outdated forgotten deps left around.
Plus being anything configured in the config (well, not mandatory, but that's the typical way) you have a fully reproducible system, maybe not binary-reproducible meaning "packageA now is version x.y" when you rebuild the system, but anything could be rebuild in the current state of nixpkgs/guix states from few kb of text, typically versioned in a repo. Every update does not overwrite anything, if put some new versions in a special tree /nix/store o /gnu/store and updates symlinks accordingly, if it does not work you restore the previous state instead/before garbage collection.
Practically it do the same of IllumOS with IPS (the package manager) integrated with zfs (and the bootloader), here instead of zfs clones and snapshots you have a poor man's version with symlinks.
There is no isolation by default, meaning it's a single system, but you can "portion" the system in various ways. Of course on Linux there are no IllumOS zones of FreeBSD jails, the state of paravirtualisation it's very behind those unices.
You can choose for package A to se package B and C, but not D, different versions means simply different packages because you have package alone, let's say the current stable version but also package_major_minor for various supported major or minor version. As well as you can choose to fetch sources from a specific commit from a public repo, build them and link them in the system.
Every package is not "isolated" in the container self, like small userlands on a common kernel, but in the sense of "having different views of the common system", so you avoid wasting gazzilion of storage and ram and CPU plus anything is still from the upstream or yourself, there are no outdated forgotten deps left around.
Plus being anything configured in the config (well, not mandatory, but that's the typical way) you have a fully reproducible system, maybe not binary-reproducible meaning "packageA now is version x.y" when you rebuild the system, but anything could be rebuild in the current state of nixpkgs/guix states from few kb of text, typically versioned in a repo. Every update does not overwrite anything, if put some new versions in a special tree /nix/store o /gnu/store and updates symlinks accordingly, if it does not work you restore the previous state instead/before garbage collection.
Practically it do the same of IllumOS with IPS (the package manager) integrated with zfs (and the bootloader), here instead of zfs clones and snapshots you have a poor man's version with symlinks.
There is no isolation by default, meaning it's a single system, but you can "portion" the system in various ways. Of course on Linux there are no IllumOS zones of FreeBSD jails, the state of paravirtualisation it's very behind those unices.