C ++ lambda按值捕获而无需提前声明变量

Question

Looking at the example on the page:

https://en.cppreference.com/w/cpp/algorithm/generate

It uses a lambda:

std::generate(v.begin(), v.end(), [n = 0] () mutable { return n++; });

the variable n is not declared anywhere prior to the lambda.

Having tried this snippet in MSVC 14 and GCC 9.1, it does work on both.

Try to find a reference to this behaviour at:

https://en.cppreference.com/w/cpp/language/lambda

but cannot find anywhere where it says that new variables can be declared in the capture region of a lambda.

Is this expected behaviour? What are the restrictions if it is?

Answer 1

In the reference you link to, it's in the lambda capture section , item number 3 in the list.

And from further down (in a "since C++14" section):

A capture with an initializer acts as if it declares and explicitly captures a variable declared with type auto

_{[Emphasis mine]}

Which explicitly explains the behavior of that capture clause.