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.
Thats interresting, thanks! Stuff for me to look into!
I also think halfway through the conversation i might have given the impression i was talking about pointers, while it was not my intention to do so. That said, the readonly/mutable reference thing is very interresting!
Ill look into what rust does/has that is like the following psuedocode :
DataBaseUser variable1 = GetDataBaseUser(20);
userService.Users.Add(variable1);
variable1 = null; // or free?
[end of function scope here, reference to heap now in list ]
No problem. I’m no guru and I’m currently on Zig but I think learning some Rust is a really fast way to hone skills that are implied by other languages.
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
'aannotation for strA and the return value, and'bfor 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.
Thats interresting, thanks! Stuff for me to look into!
I also think halfway through the conversation i might have given the impression i was talking about pointers, while it was not my intention to do so. That said, the readonly/mutable reference thing is very interresting!
Ill look into what rust does/has that is like the following psuedocode :
No problem. I’m no guru and I’m currently on Zig but I think learning some Rust is a really fast way to hone skills that are implied by other languages.