Callable
A callable is an object that can be invoked using function-call syntax.
Python How-To
callable is a Python built-in function that returns whether an object can be invoked with the call operator.
- How it is used
- Checks whether Python objects can be called and explains why functions, classes, and some instances work in callable-taking APIs.
- How deep it goes
- Defines callable and works through sorting keys and __call__-based decorators, while deferring decorator best practices.
- Examples
- Tests a doubling function, sorts poker cards with a class key, and logs execution time with a class decorator.
- What you can do after
- Build it from scratch: create a callable sorting key or class-based decorator, and check an object with callable.
The Well-Grounded Rubyist, Fourth Edition
A callable object is an object that provides a way to invoke encapsulated behavior as a function-like operation.
- How it is used
- Uses callable objects to store, pass, select, and execute behavior dynamically.
- How deep it goes
- Explains Proc creation, invocation syntax, closures, variable bindings, and method objects, while deferring exhaustive callable behavior.
- Examples
- Demonstrates Proc blocks, multiplier closures, preserved local context, counters, method binding, and alternate invocation syntax.
- What you can do after
- Apply it via Ruby Procs, lambdas, and method objects to defer, pass, select, and invoke behavior.
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Python Workout, Second Edition
A callable is a Python object that can be invoked using call syntax with parentheses.
- How it is used
- Routes user input to functions or classes selected through keyword arguments.
- How deep it goes
- Defines callability, applies it to menu dispatch, and traces class invocation through __new__ and __init__.
- Examples
- Uses menu callbacks named func_a and func_b, plus Foo(10) as a class invocation.
- What you can do after
- Apply it by building a menu that invokes keyword-selected callables and returns their results.
C++ Concurrency in Action, Second Edition
A callable object is an object that can be invoked with function-call syntax.
- How it is used
- Passes functions, function objects, or lambdas to std::thread to specify work for a new thread.
- How deep it goes
- Explains function-object copying and a declaration-parsing pitfall, but does not detail callable internals.
- Examples
- Demonstrates a function, an operator() class, a lambda, and ambiguous thread-construction syntax.
- What you can do after
- Apply callable functions, objects, or lambdas when constructing a std::thread.
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Learn C++ by Example
A callable is a function or function-like object that can be invoked with a specified argument list.
- How it is used
- Uses callable parameters to separate number-guessing feedback from the game's input and control flow.
- How deep it goes
- Explains callable types through std::function, lambdas, templates, and std::invocable, while deferring concepts to the next chapter.
- Examples
- Demonstrates callable feedback in a number-guessing game that reports whether guesses are too small or too big.
- What you can do after
- Apply it via std::function or constrained parameters to pass customizable feedback behavior into a C++ function.
Related concepts
- std::packaged_taskincludes · `std::packaged_task` is a C++ standard library class template that wraps a callable and stores its result in a shared state accessible through a future.
- functionincludes · A function is a callable program unit that performs an operation, may accept inputs, and can produce a result or side effect.
- classincludes · A class is a programming-language construct that defines a type’s structure or behavior and provides a basis for creating or representing objects.
- lambdaincludes · A lambda is a language construct that defines an unnamed function or callable, often as a value.
- callused by · A function call is an operation or expression that invokes a function or other callable, optionally supplies arguments, and initiates its execution.
- std::threadused by · A C++ standard library class that represents and manages a thread of execution.
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