GLOBALS

Globals, in programming, are identifiers with global scope that can be accessed from multiple parts of a program. A global variable or constant typically exists for the duration of execution and can be read or updated without passing it as an argument. The precise meaning and rules for globals depend on the language, with some ecosystems exposing a single global namespace and others using module- or class-scoped globals.

Scope and lifetime vary by language. In C, file-scope variables declared outside any function have static storage duration and external or internal linkage, making them visible across a translation unit and sometimes across others via extern. In Python, module-level variables are globals within that module and can be accessed from other modules through imports; reassigning them inside a function may require a global declaration. In JavaScript, the traditional global object (window in browsers, global in Node) holds true globals, but ES modules use module-scoped top-level bindings rather than globals. In Java, there are no free-floating globals, but static fields in classes serve as global-like state. In shell scripting, variables defined at the top level are visible throughout the script, though subshells run in separate processes and do not inherit those variables.

Advantages of globals include convenient data sharing and easy access to configuration or state. Disadvantages include hidden dependencies, naming collisions, harder testing and reasoning, and potential thread-safety issues in concurrent contexts. Overuse of globals tends to produce tightly coupled code and brittle software.

Best practices emphasize minimizing mutable globals. Prefer passing explicit parameters, using configuration objects, or encapsulated singletons with controlled interfaces. Use namespaces or module boundaries to reduce conflicts, and prefer immutable globals or constants for fixed values. When globals are necessary, document their usage and consider thread-safe designs.