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Lifetime in Rust

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In this ppt, we will explore how to manage lifetimes in rust in complex situations and where rust brings an upper hand over conventional languages.

These slides cover:
- Ownership and References
- Borrowing and Borrow Checking
- Explicit annotation of a lifetime
- Advanced concept of a lifetime such as a Lifetime Elision

Publié dans : Technologie
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Lifetime in Rust

  1. 1. Learn More Lifetime in Rust Ayush Prashar Software Consultant
  2. 2. Session Etiquettes ● Respect session timings, you are requested not to join sessions after a 5 minutes threshold post the session start time. ● Make sure to submit a constructive feedback for all sessions as it is very helpful for the presenter. ● Keep your mobile devices in silent mode, feel free to move out of session in case you need to attend an urgent call. ● Avoid unwanted chit chat during the session.
  3. 3. Agenda 1. Ownership 2. References 3. Dangling Reference 4. Borrow Checker 5. Lifetime Annotation 6. Lifetimes in Struct 7. Lifetime Ellison 8. Static Lifetime
  4. 4. Ownership 1. Each value in Rust has a variable known as its Owner. 2. There can be only one owner at a time. 3. When the owner goes out of scope, the value will be dropped.
  5. 5. References ● References allow usage of variables without transfer of ownership. ● It is denoted by & modifier.
  6. 6. Dangling Reference ● References which point to illegal memory. ● Is the root of memory related bugs. ● Caught at compile time.
  7. 7. How does the compiler know? ● Rust compiler has a borrow checker ● Borrow checker compares the scope of the reference variable and the variable it is referencing. ● It ensures that the subject of reference variable lives at least as long as the reference variable.
  8. 8. What if we can’t tell if a reference is valid?
  9. 9. We need to ensure that what the function may return is valid.
  10. 10. Lifetime Annotation ● A notation which describes relative lifetimes of references. ● It never changes the lifetime of the references, just constraints a specific lifetime. ● It tells that the references are valid for at least that amount of time.
  11. 11. Lifetime Annotation ● Syntax starts with an ‘ followed by a small case name which is generally a single letter. ● fn<’a> foo(param1: &’a type) -> &’a return_value ● fn<’a> foo(param1: &’a mut type)->&’a return_value
  12. 12. How do we calculate ‘a ? ● ‘a refers to the lifetime in which all the related references are valid, which is the overlap all of the references’ lifetimes. ● As a result, the smallest lifetime of all the references gets assigned to ‘a.
  13. 13. Lifetime in Structs ● Struct fields could be a reference variable. ● In structs, they imply that the instance of a structure can not out live the subject of reference of the field.
  14. 14. Lifetime Ellison ● Some coding patterns were very common and hence annotating them was considered an overhead. ● Rust identified a few of them and designed some rules. ● These rules are tested for at compile time and are used to determine the lifetimes.
  15. 15. Lifetime Ellison Rules ● Each input parameter gets its own lifetime parameter. ● If there’s only one input parameter, its lifetime is assigned to the returned value. ● If there are multiple input parameters but one of them is &self or & mut self, it’s lifetime is assigned to the returning value.
  16. 16. Lifetime Ellison ● If the compiler parses this code without any annotation and there is no reference who’s lifetime is not determined, the code is compiled successfully ● If the compiler can’t infer the lifetime of any reference, it throws an error. ● These aren’t to follow, but available at the disposal of the developer.
  17. 17. Static Lifetime ● Denotes lifetime of entire duration of the program. ● Denoted by ‘static. ● Means the reference can outlive anything. ● Anything static is directly provided inside the binary of the program.
  18. 18. Static Lifetime Variables with static lifetimes can be declared by two ways: 1. By declaring static constants static AGE: i32 = 25; 2. By declaring string literals let name: &’static str = “ayush prashar”;
  19. 19. References 1. The Rust Book(https://doc.rust-lang.org/book/index.html) 2. Stack Overflow 3. Reddit 4. Gitter Rust
  20. 20. Thank You!