PHP7以上才能安裝和使用該數據結構擴展，安裝比較簡單：
1. 運行命令 pecl install ds
2. 在php.ini中添加 extension=ds.so
3. 重啟PHP或重載配置
Collection Interface：包含本庫中所有數據結構通用功能的基本interface。 It guarantees that all structures are traversable, countable, and can be converted to json using json_encode().
Ds\Collection implements Traversable , Countable , JsonSerializable {
/* 方法 */
abstract public void clear ( void )
abstract public Ds\Collection copy ( void )
abstract public bool isEmpty ( void )
abstract public array toArray ( void )
}
Hashable Interface：which allows objects to be used as keys.
Ds\Hashable {
/* 方法 */
abstract public bool equals ( object $obj )
abstract public mixed hash ( void )
}
Sequence Interface：A Sequence 相當于一個一維的數字key數組, with the exception of a few characteristics:
Values will always be indexed as [0, 1, 2, …, size - 1].
Only allowed to access values by index in the range [0, size - 1].
Use cases：
Wherever you would use an array as a list (not concerned with keys).
A more efficient alternative to SplDoublyLinkedList and SplFixedArray.
Vector Class：Vector是自動增長和收縮的連續緩沖區中的一系列值。它是最有效的順序結構，值的索引直接映射到緩沖區中索引，增長因子不綁定到特定的倍數或指數。其具有以下優缺點：
Supports array syntax (square brackets).
Uses less overall memory than an array for the same number of values.
Automatically frees allocated memory when its size drops low enough.
Capacity does not have to be a power of 2.
get(), set(), push(), pop() are all O(1).
但是 shift(), unshift(), insert() and remove() are all O(n).
Ds\Vector::allocate — Allocates enough memory for a required capacity. Ds\Vector::apply — Updates all values by applying a callback function to each value. Ds\Vector::capacity — Returns the current capacity. Ds\Vector::clear — Removes all values. Ds\Vector::__construct — Creates a new instance. Ds\Vector::contains — Determines if the vector contains given values. Ds\Vector::copy — Returns a shallow copy of the vector. Ds\Vector::count — Returns the number of values in the collection. Ds\Vector::filter — Creates a new vector using a callable to determine which values to include. Ds\Vector::find — Attempts to find a value's index. Ds\Vector::first — Returns the first value in the vector. Ds\Vector::get — Returns the value at a given index. Ds\Vector::insert — Inserts values at a given index. Ds\Vector::isEmpty — Returns whether the vector is empty Ds\Vector::join — Joins all values together as a string. Ds\Vector::jsonSerialize — Returns a representation that can be converted to JSON. Ds\Vector::last — Returns the last value. Ds\Vector::map — Returns the result of applying a callback to each value. Ds\Vector::merge — Returns the result of adding all given values to the vector. Ds\Vector::pop — Removes and returns the last value. Ds\Vector::push — Adds values to the end of the vector. Ds\Vector::reduce — Reduces the vector to a single value using a callback function. Ds\Vector::remove — Removes and returns a value by index. Ds\Vector::reverse — Reverses the vector in-place. Ds\Vector::reversed — Returns a reversed copy. Ds\Vector::rotate — Rotates the vector by a given number of rotations. Ds\Vector::set — Updates a value at a given index. Ds\Vector::shift — Removes and returns the first value. Ds\Vector::slice — Returns a sub-vector of a given range. Ds\Vector::sort — Sorts the vector in-place. Ds\Vector::sorted — Returns a sorted copy. Ds\Vector::sum — Returns the sum of all values in the vector. Ds\Vector::toArray — Converts the vector to an array. Ds\Vector::unshift — Adds values to the front of the vector.
Deque Class：“雙端隊列”的縮寫，也用于Ds\Queue中，擁有head、tail兩個指針。The pointers can “wrap around” the end of the buffer, which avoids the need to move other values around to make room. This makes shift and unshift very fast — something a Ds\Vector can't compete with. 其具有以下優缺點：
Supports array syntax (square brackets).
Uses less overall memory than an array for the same number of values.
Automatically frees allocated memory when its size drops low enough.
get(), set(), push(), pop(), shift(), and unshift() are all O(1).
但Capacity must be a power of 2.insert() and remove() are O(n).
Map Class：鍵值對的連續集合，幾乎與數組相同。鍵可以是任何類型，但必須是唯一的。如果使用相同的鍵添加到map中，則將替換值。其擁有以下優缺點：
Keys and values can be any type, including objects.
Supports array syntax (square brackets).
Insertion order is preserved.
Performance and memory efficiency is very similar to an array.
Automatically frees allocated memory when its size drops low enough.
Can't be converted to an array when objects are used as keys.