Lambda expressions
An inline, anonymous function you can define right where you need it.
auto isEven = [](int x) { return x % 2 == 0; };
isEven(4); // true
std::sort(v.begin(), v.end(), [](int a, int b) { return a > b; }); // descending[] is the capture clause, () the parameters — same as any normal function from there.
Capturing outside variables
int threshold = 10;
auto aboveThreshold = [threshold](int x) { return x > threshold; }; // by value, a snapshot
auto modifyOutside = [&threshold](int x) { threshold = x; }; // by reference, live link
auto captureAll = [=] { ... }; // everything by value (avoid - unclear what's used)
auto captureAllRef = [&] { ... }; // everything by reference (avoid - same reason)Want to call a member function or touch a member variable inside a lambda? Capture this.
Storing one for later
std::function<bool(int,int)> comparator = [](int a, int b) { return a > b; };Every lambda has its own unique, compiler-generated, unnamable type — auto works for storing one immediately, but if you need to pass it around, return it, or store it as a class member, wrap it in std::function instead.