Implicit output
An implicit output is an observable effect of a computation, such as changing external state or raising an exception, not represented by its return value.
Grokking Simplicity
An effect of a function that changes external state or performs an observable operation rather than returning the result directly.
- How it is used
- Uses implicit outputs to identify hidden coupling in actions and guide refactoring toward explicit return values.
- How deep it goes
- Explains definitions, testing consequences, copy-on-write extraction, and asynchronous callbacks, but does not develop implementation details beyond JavaScript examples.
- Examples
- Uses shopping-cart mutation, cart-total calculation, DOM updates, shipping icons, and asynchronous cost and shipping calculations.
- What you can do after
- Diagnose/debug with it by locating hidden outputs, then replace them with return values or callbacks to improve testing and reuse.
Unit Testing Principles, Practices, and Patterns
A hidden output is an effect of a computation, such as a side effect or exception, that is not represented by its return value.
- How it is used
- Explains why side effects complicate functional reasoning and testing.
- How deep it goes
- Defines hidden outputs, identifies them through referential transparency, and contrasts them with explicit method outputs.
- Examples
- Uses Increment, AddComment, CalculateDiscount, side effects, and exceptions as concrete comparisons.
- What you can do after
- Diagnose hidden behavior by comparing a method call with its return value and inspecting state changes or exceptions.
Read how Unit Testing Principles, Practices, and Patterns explains implicit output →
Related concepts
- return valuealternative to · A return value is the result produced by a function, method, or operation and supplied to the code that invoked it.
- DOM updateincludes · A modification to the Document Object Model that changes a document's represented content, structure, or presentation.
- 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.
- mathematical calculationcontrasts with · A mathematical calculation is an operation or expression that derives a result from one or more input values.
- 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.
- generationkind of · Generation is the computational production of outputs from supplied inputs or context, often by applying a model to produce predictions or new content.
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