Optional function argument
An optional function argument is an input corresponding to a parameter that a caller is not required to supply because omission is permitted by the function's interface.
The Well-Grounded Rubyist, Fourth Edition
An optional parameter is a method parameter whose value can be omitted because a default value is specified.
- How it is used
- Makes Ruby method calls flexible when callers need not supply every positional or keyword value.
- How deep it goes
- Works through defaults, starred arrays, mixed-parameter binding, and invalid ordering; treats keyword arguments separately.
- Examples
- Compares method calls that use defaults, override them, fill catch-all arrays, or fail for too few arguments.
- What you can do after
- Build it from scratch using valid Ruby signatures with optional positional or keyword parameters, and predict argument assignments.
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Essential TypeScript 5, Third Edition
An optional parameter is a function parameter that may be omitted by the caller and is denoted with a question mark in TypeScript.
- How it is used
- Allows callers to omit an argument when a function can operate without its value.
- How deep it goes
- Explains declaration syntax, required-parameter ordering, omitted values, and the need for a fallback; does not explore compiler internals.
- Examples
- Uses a tax calculation called with one or two arguments, plus a rejected call with three.
- What you can do after
- Apply it in TypeScript functions to permit omitted arguments while handling the resulting `undefined` value.
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ASP.NET Core in Action, 3e
An optional parameter is a handler or method parameter that may receive no corresponding input and instead accept a null or default value.
- How it is used
- Handles missing route, query, or body input without preventing a minimal API handler from running.
- How deep it goes
- Explains nullable syntax and runtime null behavior, while treating default parameter values as a separate feature.
- Examples
- Demonstrates /stock/{id?} with int?, a nullable Product body, and contrasting required-parameter failure behavior.
- What you can do after
- Apply optional arguments via ASP.NET Core minimal APIs to accept missing values and handle null explicitly.
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Pro Angular 16
An optional parameter is a function parameter that may be omitted when the function is called.
- How it is used
- Allows callers to omit selected arguments, especially when constructing product models whose properties may come from HTML forms.
- How deep it goes
- Defines the `?` syntax, omitted-value behavior, inferred `undefined`, and distinction from a required `string | undefined` parameter.
- Examples
- Uses a string-printing function with a fallback and Product constructors with omitted model fields.
- What you can do after
- Apply optional parameters to let calls omit arguments or create partially populated Product objects.
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Related concepts
- parameterkind of · A parameter is a value or variable that specifies or controls a characteristic, computation, or behavior of a function, model, operation, or request.
- inputkind of · An input is a value, information, or signal supplied to a system, computation, or interface for processing or to influence its behavior.
- default valuealternative to · A default value is a predefined or automatically supplied value used when an expected input, argument, field, or configuration setting is omitted or unspecified.
- integerconfigured by · An integer is a whole number with no fractional part, including negative numbers, zero, and positive numbers.
- functionpart of · A function is a defined operation that maps inputs to outputs and, when implemented as a callable program unit, may also produce effects.
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