Arrays And Collections: Introduction
Hack includes diverse range of array-like data structures.
Hack arrays are value types for storing iterable data. The types
available are vec, dict and keyset. When in doubt, use Hack
arrays.
Collections are object types for storing iterable data. The types
available include Vector, Map, Set, Pair and helper
interfaces.
Quickstart
You can create Hack arrays as follows:
$v = vec[2, 1, 2];
$k = keyset[2, 1];
$d = dict['a' => 1, 'b' => 3];
The Hack Standard Library
There are many helpful functions in the C, Vec, Keyset and Dict
namespaces, which are a part of the Hack Standard Library (HSL).
For more information on included HSL namespaces, see Hack Standard Library: Namespaces.
// The C namespace contains generic functions that are relevant to
// all array and collection types.
C\count(vec[]); // 0
C\is_empty(keyset[]); // true
// The Vec, Keyset and Dict namespaces group functions according
// to their return type.
Vec\keys(dict['x' => 1]); // vec['x']
Keyset\keys(dict['x' => 1]); // keyset['x']
Vec\map(keyset[1, 2], $x ==> $x + 1); // vec[2, 3]
Arrays Cheat Sheet
| Operation | vec |
dict |
keyset |
|---|---|---|---|
| Initialize empty | $v = vec[]; |
$d = dict[]; |
$k = keyset[]; |
| Literal | $v = vec[1, 2, 3]; |
$d = dict['foo' => 1]; |
$k = keyset['foo', 'bar']; |
| From Another Container* | $v = vec($container); |
$d = dict($keyed_container); |
$k = keyset($container); |
| Keys from Container* | $v = Vec\keys($container); |
N/A | $k = Keyset\keys($container); |
| Add Elements | $v[] = 4; |
$d['baz'] = 2; |
$k[] = 'baz'; |
| Bulk Add Elements | $v = Vec\concat($t1, $t2) |
$d = Dict\merge($kt1, $kt2) |
$k = Keyset\union($t1, $t2) |
| Remove Elements | Remove-at-index is unsupported; Vec\drop($v,$n), Vec\take($v,$n); $first=C\pop_front(inout $x), $last=C\pop_back(inout $x) |
unset($d['baz']); |
unset($k['baz']); |
| Key Existence | C\contains_key($v, 1) |
C\contains_key($d, 'foo') |
C\contains_key($k, 'foo') |
| Value Existence | C\contains($v, 3) |
C\contains($d, 2) |
Use C\contains_key($k, 'foo') |
| Equality (Order-Dependent) | $v1 === $v2 |
$d1 === $d2 |
$k1 === $k2 |
| Equality (Order-Independent) | N/A | Dict\equal($d1, $d2) |
Keyset\equal($k1, $k2) |
| Count Elements (i.e., length, size of array) | C\count($v) |
C\count($d) |
C\count($k) |
| Type Signature | vec<Tv> |
dict<Tk, Tv> |
keyset<Tk> |
| Type Refinement | $v is vec<_> |
$d is dict<_, _> |
$k is keyset<_> |
Awaitable Consolidation |
Vec\from_async($v) |
Dict\from_async($d) |
Keyset\from_async($x) |
* $container can be a Hack Array or Hack Collection
Arrays Conversion Cheat sheet
Prefer to use Hack arrays whenever possible. When interfacing with legacy APIs that expect older Containers, it may be easier to convert. Here's how:
| Converting | To Vector |
To Map |
To Set |
|---|---|---|---|
dict |
N/A | new Map($d) |
N/A |
dict keys |
Vector::fromKeysOf($d) |
N/A | Set::fromKeysOf($d) |
dict values |
new Vector($d) |
N/A | new Set($d) |
vec |
new Vector($v) |
new Map($v) |
new Set($v) |
keyset |
new Vector($k) |
new Map($k) |
new Set($k) |