How deeply does C++ Concurrency in Action, Second Edition cover callable?

Explains function-object copying and a declaration-parsing pitfall, but does not detail callable internals.

Callable

As explained in C++ Concurrency in Action, Second Edition

A callable object is an object that can be invoked with function-call syntax.

A callable can be invoked with function-call syntax. In C++, std::thread accepts callable types, including functions and objects with a function-call operator. When a function object is passed to a thread, it is copied into the new thread’s storage and invoked there, so its copy should behave like the original. section 2.1.1

class background_task
{
public:
    void operator()() const
    {
        do_something();
        do_something_else();
    }
};
background_task f;
std::thread my_thread(f);

A class with operator() can supply the work for a thread; the object is copied into the thread. section 2.1.1

Common callable forms and a syntax pitfall:

A function can be passed directly to std::thread. section 2.1.1
A lambda can provide the work inline. section 2.1.1
std::thread my_thread(background_task()); can be parsed as a function declaration rather than an object definition. Extra parentheses or brace initialization avoid this ambiguity. section 2.1.1

std::thread my_thread((background_task()));
std::thread my_thread{background_task()};


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These alternatives use extra parentheses or braces to ensure my_thread is declared as an object. section 2.1.1

How C++ Concurrency in Action, Second Edition covers it

Cover of C++ Concurrency in Action, Second Edition

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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.

This explainer was generated by Manning's knowledge graph from the text of C++ Concurrency in Action, Second Edition. The section links point to the parts of the book it draws on.