← All notes

Answer: Vec<T>, also known as a vector, lets you store more than one value in a single data structure that puts all the values next to each other in memory. Vectors can only store values of the same type. (S1)

Creating one

• Rust conveniently provides the vec! macro, which will create a new vector that holds the values you give it. (S1)
• More often, you'll create a Vec<T> with initial values, and Rust will infer the type of value you want to store. (S1)
• Like slices, their size is not known at compile time, but they can grow or shrink at any time. (S2)
• The capacity indicates how much memory is reserved for the vector; when that threshold needs to be surpassed, the vector is reallocated with a larger capacity. (S2)

Reading elements

• There are two ways to reference a value stored in a vector: via indexing or by using the get method. (S1)
• When we use the get method with the index passed as an argument, we get an Option<&T> that we can use with match. (S1)
• Indexing with [] will cause the program to panic when it references a nonexistent element. (S1)

Borrowing rules still apply

• Recall the rule that states you can't have mutable and immutable references in the same scope. (S1)
• That rule applies when we hold an immutable reference to the first element in a vector and try to add an element to the end. (S1)
• Iterating over a vector, whether immutably or mutably, is safe because of the borrow checker's rules. (S1)

Claims

• id: C1 claim: Vectors store values of one type next to each other in memory. source: S1 evidence: "Vectors can only store values that are of the same type."
• id: C2 claim: get returns an Option<&T>. source: S1 evidence: "we get an Option<&T> that we can"
• id: C3 claim: A vector is reallocated when it outgrows its capacity. source: S2 evidence: "the vector is reallocated with a larger capacity."
• id: C4 claim: Vectors can grow or shrink at any time. source: S2 evidence: "time, but they can grow or shrink at any time."

Sources

• [S1] Storing Lists of Values with Vectors - The Rust Programming Language. The Rust Programming Language. https://doc.rust-lang.org/book/ch08-01-vectors.html . License: MIT or Apache-2.0 (rust-lang/book; Copyright (c) 2010 The Rust Project Developers; https://github.com/rust-lang/book/blob/main/LICENSE-MIT). Accessed 2026-11-04.
• [S2] Vectors - Rust By Example. Rust by Example. https://doc.rust-lang.org/rust-by-example/std/vec.html . License: MIT or Apache-2.0 (rust-lang/rust-by-example; Copyright (c) 2014 Jorge Aparicio; https://github.com/rust-lang/rust-by-example/blob/master/LICENSE-MIT). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_msgvp1yr,
  author = {{iinventedlight}},
  title = {{Rust vectors: Vec<T>, indexing versus get, and borrowing}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/rust-vectors/},
  note = {Permanent ID iil:note:msgvp1yr. License: CC-BY-4.0.},
}

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