Implicit input
An implicit input is a dependency on surrounding state or context that affects a computation without appearing as an explicit function argument.
Grokking Simplicity
An input obtained by a computation from surrounding state or context rather than supplied explicitly as a function argument.
- How it is used
- Uses implicit inputs to distinguish actions from calculations and guide incremental improvements to function design.
- How deep it goes
- Explains hidden reads, global-state coupling, and argument conversion through worked shopping-cart refactorings; it stops short of eliminating all actions.
- Examples
- Demonstrates shopping carts, shipping icons, tax calculations, DOM updates, and asynchronous cart totals.
- What you can do after
- Diagnose/debug with it by locating hidden global reads and converting them into arguments to improve reuse and testability.
Unit Testing Principles, Practices, and Patterns
A hidden input is an implicit dependency on internal or external state that affects a computation without appearing as an explicit argument.
- How it is used
- Defines hidden state as a criterion for separating business logic from side effects and selecting an appropriate unit-testing style.
- How deep it goes
- Explains the definition, testing consequence, and database refactoring trade-off, but stops short of implementation details beyond the method signature.
- Examples
- Uses Increment with internal state and AuditManager.AddRecord with a database dependency to contrast explicit and hidden inputs.
- What you can do after
- Diagnose hidden dependencies, predict when output-based testing becomes unavailable, and choose between eager data gathering and delegated lookup.
Read how Unit Testing Principles, Practices, and Patterns explains implicit input →
Related concepts
- explicit inputalternative to · An explicit input is a value supplied directly by a caller through an argument at a function's invocation site.
- command-line argumentalternative to · A command-line argument is a value supplied to a program when it is invoked, either as positional input or as an option that configures its behavior.
- actionused by · An action is a choice or operation selected or performed by an actor that can affect a system or environment or produce an outcome.
- mathematical calculationcontrasts with · A mathematical calculation is an operation or expression that derives a result from one or more input values.
- global variableused by · A global variable is a variable whose binding is accessible from broad program or module scope according to the language’s name-resolution rules.
- testabilitycontrasts with · Testability is the degree to which a system’s behavior can be exercised and evaluated effectively, efficiently, and reliably through testing.
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