hash-lists

ObjectPascal Implementation of the Perl Data Structure known as %hash inspired by the Documentation at https://www.perl.com/pub/2002/10/01/hashes.html/

Implementation

The Hash Lists are implemented as 2 Dynamic Arrays which are the Bucket and the List of Buckets.
As Hash Function it uses the sdbm / ndbm Algorithm
The best Application are those which can be configured by human beings. Thus the Properties that determine all over Usage Performance are adjustable by the User according to the Use Case.

Performance

The Performance of the Hash List depends heavily on the GrowFactor and LoadFactor.
Adjusted correctly it achieves an Insertion and Lookup Speed like the similiar Structure for the Rust Programming Language, the Rust std::collections::HashMap.
For Insertions it is more than 10 times faster than the Generics.Collections.TFastHashMap Class.
It also beats the speed of its reference the Perl %hash on the Insert Operation on larger data sets.

If you expect a fix amount of elements to be inserted. (Perhaps comming from a SQL Query with fix Limit) it is beneficial to set the List size beforehand with the Capacity Property

Documentation

The Documentation of the Data Structures was generated with the fpdoc tool and be found at:
Project Documentation in TXT format
The Class Diagramm kann be found at:
Class Diagram for the Unit 'pointerhash'

Motivation

Using the FCL Data Types TFPObjectHashTable and TFPStringHashTable the performance of the Application dropped drastically. Inserting 9 Keys in 4 Objects took 20ms while the Perl-Script doing the same task finished the Job already in 15 ms.
Learning about highly performant Perl Data Structure was the inspiration to try to implement a Library that could achieve the same Tasks in much less time.
It also implements the missing Features for the Perl %hash as to know the Element Count and Iterating over the Data Structure without the need to copy the Keys.

Disclaimer

The TPLPointerHashList will not free the Values stored in it. You need to free them yourself after usage.
Though the TPLObjectHashList does free the TObjects stored in it calling the TObject.Free() Method.
The TPLStringHashList copies the String Values and frees them on Destruction.