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Course Intermediate

Ownership and the Memory Model

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By the end of this course

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01

Ownership Rules

How visible in the type a value's location is, how the single-owner rule forces a move, how borrowing grants access without transferring ownership, how a slice views data without taking ownership, and what the checker that tests all of this at compile time actually guarantees.

  1. 01 Stack and Heap A fourteen-value measurement core runs and places every value's life into one of four classes — scope end, where it was moved, an explicit call, together with its container; the result is fixed at 6/3/1/4. It measures that values ending at scope end finish in the exact reverse of their declaration order, and that a heap-allocated value drops into the same ledger.
  2. 02 Ownership and Moves Moving a value into a function, into an inner scope, and into a struct field all fall into the same class (where it was moved), and in all three the value ends exactly once; that the old binding cannot be used after a move is a rule the compiler tests at compile time, while the new owner can use the value without any problem.
  3. 03 Borrowing A value can be read and written through a reference without ever giving up ownership: while the borrow lasts no record forms in the ledger, and once the borrow's scope closes the value is still accessible in its owner. A shared and a mutable reference exclude each other; a reference's scope always has to stay inside its source's scope.
  4. 04 Slices A slice views a specific range of a string or a growable array without taking ownership: the slice gets used, the slice ends, but the source never ends. A slice's length derives from the source, and an empty slice is valid; the source cannot be changed while the slice lives, and a change goes through without a problem once the slice ends.
  5. 05 The Borrow Checker The borrow checker tests a value's ownership and borrowing rules at compile time; three rejection examples (a live borrow during a move, mutating while reading, returning a reference to a local owner) are always described in prose, with an accepted solution run alongside each. Two different solutions doing the same job can produce the same ledger record; code that follows the borrowing rules can still give a wrong result — the checker guarantees not correctness, only ownership discipline.

02

Lifetimes

The establishment of a reference's validity range as a concept, the requirement to write an annotation when two sources' lives diverge, the rules by which the compiler derives an unwritten annotation, and the condition that holding a reference in a struct's field places on the struct's own life.

  1. 01 The Lifetime Concept Establishes that the source range over which a reference is valid is not a runtime object, only a range the compiler checks. The range shown to be checked in the Borrow Checker lesson is given a name here, and it is measured that two independent references' ranges need not be nested.
  2. 02 Explicit Lifetime Annotations When a function takes multiple references and returns one of them, which input the returned reference is tied to cannot be inferred from the source alone, and an explicit lifetime annotation is required. It is measured that the annotation neither extends nor shortens a reference's life, only writes an existing relationship into the source, and that the compiler validates this writing as a request.
  3. 03 Lifetime Elision Rules Measures the rules the compiler uses to derive a lifetime annotation that is not written in a signature. The same signature is written and run in both explicit and implicit form, and both are shown to give the same behavior; a rejection-acceptance pair tests a signature elision does not cover, where the annotation stays mandatory.
  4. 04 References in Structs Measures the condition that holding a reference in a struct's field places on the struct's own life: a struct cannot outlive the data it refers to. The same data is held both by moving it into a struct and by borrowing it into one; it is compared by running the code that a moved field ends together with the struct, while borrowed data ends after the struct.

03

Shared Ownership

How heap-allocated single ownership makes a self-referential type possible, how a counter determines a shared value's lifetime, that same counter's atomic form across threads, borrow checking's move to runtime, and how two values holding onto each other keeps a lifetime from ever ending.

  1. 01 Heap-Allocated Single Ownership How a value can still have exactly one owner while it lives on the heap, how a value that ends together with its container depends on the container's own order, and how that single ownership makes a self-referential type possible.
  2. 02 Reference Counting How an Rc value's counter rises with every clone and falls with every end, and how the value reaches the ledger only once the counter hits zero, is measured; that taking a reference never changes this counter, and that what decides the end is not which copy is dropped but how many remain, is shown.
  3. 03 Atomic Reference Counting How the same counting mechanism, built with Arc, produces exactly the same end record — with the difference lying not in behavior but in how the counter is updated — is measured; which context it can be used in is not discussed here, since that is the subject of the Concurrency and Asynchronous Rust course. That shared data can only be read through an Arc, never modified directly, is also shown.
  4. 04 Interior Mutability How the same 'one writer or many readers' rule is tested with a counter at runtime instead of compile time is measured; that a binding itself can stay immutable while the value inside it becomes modifiable through RefCell, and that a failed borrow attempt can be taken as a bool result instead of a panic, are shown. The rule does not disappear, it changes location.
  5. 05 Reference Cycles How, when two values hold each other through Rc via RefCell, the strong counter never drops to zero and no record ever appears in the ledger — the course's only leak — is measured. That a weak reference breaks the same reference cycle without raising the counter, and that once broken the ledger produces two records at once, is run; strong and weak counter values are printed.

Final exam

Ownership and the Memory Model — Final Exam

In preparation

This course's question bank is not complete yet. The exam opens here automatically once enough questions are added.

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