FetchValue

FetchValue is a generic operation used to retrieve a value associated with a key or path from a data source. It can be implemented as a function, method, or non-blocking routine, and appears in libraries ranging from configuration management to data parsing. The data source may be a map or dictionary, a JSON or YAML object, a database row, or a remote API response. The function typically accepts a source and a key or path and returns the corresponding value; behavior for missing keys varies: some implementations return a default value, some raise an exception, and others return a sentinel like null or undefined.

Asynchronous variants return a promise or future and resolve to the value when available. In such contexts, fetchValue may accept a callback or be used with async/await patterns. Some implementations also support streaming or partial retrieval for large objects.

Support for nested paths and type safety: Path expressions can address nested objects; many libraries provide type hints or generics to enforce expected value types. Some fetchValue variants perform implicit type conversion or validation.

Common usage patterns include safe fetch with a default, strict fetch that signals absence via errors, and optional chaining to gracefully handle missing components. Caching and memoization are often employed to improve performance.

Implementation considerations include distinguishing between a missing value and a concrete null, handling nullability and errors consistently, and securing data sources to avoid leaking sensitive information.

Related terms include getValue, lookup, and accessors, as well as getOrDefault or defaultValue helpers that standardize fallback behavior.