identifierswhen

identifierswhen is a theoretical concept in programming language design that describes a rule or annotation binding an identifier to a condition. The term is not part of a standardized language specification and appears mainly in academic discussions and speculative proposals. It is used to express contextual binding, where the availability of a name depends on runtime or configuration predicates rather than solely on lexical scope.

In the proposed model, an identifier carries a predicate, such as when featureX is enabled or when env equals production. The binding of the name is resolved only if the predicate evaluates to true; otherwise the identifier is hidden or becomes unresolved in that scope. This can interact with existing scoping and resolution rules and may require explicit tooling support to avoid ambiguity.

Potential motivations include refining modularity in configurable software, supporting feature-flag driven code paths, or modeling conditional namespaces in language design research. Proponents argue that identifierswhen can improve readability of configuration-dependent code and help static analyzers reason about visibility. Critics point to increased complexity in name resolution, potential confusion for programmers, and compatibility challenges with existing tooling, compilers, and editors.

As a niche concept, identifierswhen has not been adopted as a standard feature in mainstream languages. It overlaps with related ideas such as conditional compilation, feature flags, and guarded or scoped bindings. See also identifiers, conditional compilation, scoping, feature flags.