CONCAT

Concat, short for concatenation, is the operation of joining two or more sequences to form a new sequence. It applies to strings, arrays, lists, or byte sequences, and is fundamental in text processing, data formatting, and assembling data programmatically. The term derives from Latin con- “together” and catena “chain.”

In programming languages, concatenation is expressed by various operators or functions. In many languages the plus sign (+) appends strings, while in PHP the dot operator (.) is used for string concatenation. SQL databases commonly provide a CONCAT function, and some dialects support a concatenation operator such as || or a plus sign. In Python and JavaScript, the + operator concatenates strings; in Java, strings concatenation is possible with + and is often optimized behind the scenes by a string builder when used repeatedly in a loop.

Efficiency and implementation considerations often center on the mutability of the sequence type. Strings are typically immutable, so naive repeated concatenation can create many intermediate copies and hurt performance. Best practices include using a dedicated builder or buffer (such as StringBuilder in Java, or join methods that aggregate a collection of fragments in many languages) for large constructions. For arrays or lists, concatenation yields a new array or list containing the elements of the merged inputs.

Applications of concatenation include building file paths and URLs, formatting messages, templating, and assembling data records. It is a core primitive in text processing, data processing, and software development across languages and systems.