Lambdas.

Under the Covers of C++ Lambdas: Captures, Captures, Captures

by Andreas Fertig

From the article:

Lambda Capturing syntax allows us to quickly “wrap” a variable from the outside scope and then use it in the lambda body. We also know that under the hood the compiler translates lambda into a closure type… but what happens to those captured variables? Are they translated to public data members or private? See the newest guest post from Andreas to understand this tricky problem...