When does C++ use lambda expressions

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F.50: use lambda expressions when you don't want to use functions (such as reading local variables, accessing local functions)

Reason (reason)

Functions cannot use local variables outside the function body, nor can they be defined in the local scope; if you need this functionality, it is better to use lambda expressions if possible, otherwise you need to implement the function object yourself. On the other hand, lambda expressions and function objects cannot be overloaded; if you need to overload, functions are more appropriate (the method of overloading lambda expressions by twists and turns is too advanced). If both ways are available, it is better to use functions; use the simplest tool that meets your needs.

Example (sample)

/ / writing a function that should only take an int or a string//-- overloading is naturalvoid f (int); void f (const string&)

/ / writing a function object that needs to capture local state and appear// at statement or expression scope-- a lambda is naturalvector v = lots_of_work (); for (int tasknum = 0; tasknum < max; + + tasknum) {pool.run ([=, & v] {/ *. Process 1 / max-th of v, the tasknum-th chunk... * /});} pool.join (); Exception (exception)

Normal lambda expressions are useful because they provide a concise way to implement function templates; an ordinary function template requires even a slightly more complex syntax to do the same thing. But once all functions can have conceptual parameters in the future, this advantage is likely to disappear in the future.

Translator's note: Concept is a new feature that will be introduced by Category 20.

Enforcement (implementation recommendations)

Alarm when a named non-ordinary lambda expression that does not get any variables and exists in the global scope (such as auto x = [] (int) {/ *... * /};) is used.

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