Appendable

Appendable is an adjective used in computing and data structures to describe an object or data container that can have data added to its end via an append operation. An appendable object is typically modified in place rather than creating a new object, though some languages offer both mutable and immutable variants.

In practice, appendable containers include dynamic arrays, string builders, and buffers. The key property is that appending an item increases the length and preserves existing content. Performance often relies on amortized analysis; mutable dynamic arrays grow capacity to accommodate new elements while keeping append time near constant on average. Strings in many languages are immutable, so repeated appends may create new strings unless a builder-like object is used.

In programming languages, there is often a formal interface or protocol for appendable objects. For example, Java defines the Appendable interface, which declares methods to append characters or sequences and is implemented by classes such as StringBuilder and StringBuffer. Implementations enable seamless chaining and composing of text data, making append operations a common pattern in I/O and string construction.

Other contexts use the term to describe files or logs that support appending data at the end, rather than modifying existing content. Appendable semantics are valued for simplicity, data integrity, and auditability in systems that accumulate events over time. Design considerations include mutability, thread-safety, and the distinction between in-place appends and building new instances.