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Why are multiple package versions a problem? In Rust they Just Work.

stubish 5y ago
It can mess up when you are dealing with global resources. ie. two different versions of the same package both attempting to initialize global state (memory, filesystem, databases, whatever) will usually conflict with itself. Often in ways that will crash or even cause data loss.
- pcwalton 5y ago
  I've never had that happen in Rust because multiple versions of a crate effectively live in completely separate worlds: they have their own copies of globals, for example. Can you name an example of multiple versions conflicting at runtime in Rust?
  - stubish 5y ago
    By globals, I mean global resources outside of the codes namespace. It may not even be a resource in the process, such as a log file or temporary directory or a database. If you have two versions of a crate in their completely separate worlds, and call both of their init_logging() functions to log to a file specified by an environment variable, things are likely to go pear shaped when they stomp over each others log file. I'm a Rust novice, but the example I tripped over in Go was https://github.com/golang/glog https://github.com/golang/glog. It has a module level init() initialization routine that makes calls to the stdlib flags package, manipulating the default command line flags (a global resource). If you ended up with multiple versions of glog via transient dependencies, your program would panic on startup as the second version's init() would make calls only allowed to be called once. Rust thankfully avoids this particular one by requiring initialization to be called by main() (apart from the hack described in the article).
    - cute_boi 5y ago
      First of all, in Rust global are highly discouraged and if there are shared resources then they should be defined or initialized by binary writer not the library writer Otherwise the library is not of good quality. Regarding go I can't say as I have never programmed go.

It can mess up when you are dealing with global resources. ie. two different versions of the same package both attempting to initialize global state (memory, filesystem, databases, whatever) will usually conflict with itself. Often in ways that will crash or even cause data loss.

pcwalton 5y ago
I've never had that happen in Rust because multiple versions of a crate effectively live in completely separate worlds: they have their own copies of globals, for example. Can you name an example of multiple versions conflicting at runtime in Rust?
- stubish 5y ago
  By globals, I mean global resources outside of the codes namespace. It may not even be a resource in the process, such as a log file or temporary directory or a database. If you have two versions of a crate in their completely separate worlds, and call both of their init_logging() functions to log to a file specified by an environment variable, things are likely to go pear shaped when they stomp over each others log file. I'm a Rust novice, but the example I tripped over in Go was https://github.com/golang/glog https://github.com/golang/glog. It has a module level init() initialization routine that makes calls to the stdlib flags package, manipulating the default command line flags (a global resource). If you ended up with multiple versions of glog via transient dependencies, your program would panic on startup as the second version's init() would make calls only allowed to be called once. Rust thankfully avoids this particular one by requiring initialization to be called by main() (apart from the hack described in the article).
  - cute_boi 5y ago
    First of all, in Rust global are highly discouraged and if there are shared resources then they should be defined or initialized by binary writer not the library writer Otherwise the library is not of good quality. Regarding go I can't say as I have never programmed go.