CODEWITHSUNDEEP
c++c++11
Akanksh
Akanksh

Reputation: 1310

C++ lambda capture by value without declaring variable earlier

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?

Upvotes: 2

Views: 655

Answers (1)

Some programmer dude
Some programmer dude

Reputation: 409482

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.

Upvotes: 6

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