FLAGMUTABLE

FLAGMUTABLE is a naming convention used in software development to denote a flag that marks an object, data, or handle as mutable. In many languages and libraries, flags are implemented as integer constants where a specific bit represents mutability. The flag is typically combined with other flags to configure behavior at creation time or to gate access by other components. When set, the flag signals that the underlying object may be changed after creation; when unset, the object is treated as immutable by the system or API.

In Android, there is a concrete use of a similar flag named FLAG_MUTABLE (and its counterpart FLAG_IMMUTABLE) for PendingIntent objects. Since Android 12 (API level 31), apps must explicitly declare the mutability of a PendingIntent by supplying one of these flags at creation time. The choice affects how the system and other apps may interact with the intent’s extras; using FLAG_IMMUTABLE reduces the risk of unintended modification and is generally encouraged unless modification is required. FLAG_MUTABLE, by contrast, allows the receiver to alter the PendingIntent after it's created.

Usage considerations: choose immutability when possible to improve security and predictability. When a receiver must modify the intent data or its extras, use a mutable flag and ensure only trusted components can rely on that mutability. Different platforms may implement FLAGMUTABLE with different semantics, so consult the relevant API docs for exact behavior.

See also: immutability, mutability, PendingIntent, Android Security.