• 0 Posts
  • 4 Comments
Joined 11 months ago
cake
Cake day: November 26th, 2023

help-circle

  • It’s new to me, I think it’s saying that your system is built up by you declaring what you want in a file, a single source that everything comes from.

    It’s atomic because each action the system takes is carefully completed rather than bailing out and requiring you to fix something.

    It’s immutable meaning you declare how you want things to be set up and then critical changes stem from those declarations and nothing else. You would obviously generate preferences, save data, etc. but the files that make the system / packages work are carefully locked.

    It’s like the concept of flatpaks + structured system defining + modern common sense OS operations?



  • You use lifetimes to annotate parameters and return values in order to tell the compiler about how long things must last for your function to be valid. You can link a specific input with the output, or explicitly separate them. If you don’t give lifetimes the language uses some basic rules to do it for you. If it can’t, eg it’s ambiguous, then it’s a compile error and you need to do it manually.

    It’s one of the harder concepts of rust to explain succinctly. But imagine you had a function that took strA and strB, used strB to find a subsection of strA, and then return a slice of strA. That slice is tied to strA. You would use 'a annotation for strA and the return value, and 'b for strB.

    Rust compiler will detect the lifetime being shorter than expected.


    Also, ownership semantics. Think c++ move semantics. Only one person is left with a good value, the previous owners just have garbage data they can’t use anymore. If you created a thing on the heap and then gave it away, you wouldn’t have it anymore to free at the end. If you want to have “multiple owners” then you need ref counting and such, which also stops this problem of premature freeing.


    Edit: one more thing: reference rules. You can have many read-only references to a thing, or one mutable reference. Unless you’re doing crazy things, the compiler simply won’t let you have references to a thing, and then via one of those references free that thing, thereby invalidating the other references.