---
name: references tutorial
---
# References — a tutorial

A **reference** in Perl is a scalar that points at another value:
an array, a hash, a subroutine, another scalar, even another
reference. References are the single mechanism that turns Perl's
three container types — scalars, arrays, hashes — into arbitrary
nested data structures.

Without references you cannot build a hash of arrays, an array of
hashes, a tree, a graph, a record with mixed fields, a callback
table, or a closure. With them, you can. This tutorial walks you
from the two reference-making operators, through the syntax for
getting the underlying value back, up to anonymous constructors,
code references, and the weak-reference trick that keeps cyclic
structures from leaking.

## Who this is for

You already write working Perl. You use arrays and hashes
comfortably, but the moment the problem calls for a hash whose
values are arrays — or an array of records, or a callback you can
store in a table — the syntax stops being obvious. That gap is what
references fill, and what this tutorial closes.

## How this tutorial is organised

Each chapter introduces one concept and stands on its own. Read
them in order the first time; jump to the relevant chapter later.

```{toctree}
:maxdepth: 1

basics
arrays-of-arrays
hashes-and-mixes
anonymous-refs
subroutine-refs
weak-refs
```

- **Basics** — the `\` operator, scalar/array/hash dereference with
  `$$x`, `@$x`, `%$x`, curly-brace disambiguation, and the `->`
  arrow for element access.
- **Arrays of arrays** — two-dimensional data, iteration patterns,
  the arrow-between-subscripts rule that makes `$m[i][j]` read as
  a matrix.
- **Hashes and mixes** — hashes of arrays, arrays of hashes, and
  the common record-table shape.
- **Anonymous references** — `[...]` and `{...}` as inline
  constructors, when to choose them over named variables.
- **Subroutine references** — `\&name`, anonymous `sub { ... }`,
  calling with `->(...)`, and how closures capture lexicals.
- **Weak references** — `Scalar::Util::weaken` and why cyclic
  structures need it.

## Related reference pages

- [`ref`](../../p5/core/perlfunc/ref) — ask a value what kind of
  reference it is.
- [`defined`](../../p5/core/perlfunc/defined) — the standard way to
  check "does this reference exist yet?" after autovivification.
- [`bless`](../../p5/core/perlfunc/bless) — the step that turns a
  plain reference into an object.