Lambda Expressions

A lambda is an anonymous, inline function — used constantly alongside STL algorithms, exactly as seen already in STL Algorithms above.

auto add = [](int a, int b) { return a + b; };
std::cout << add(2, 3) << std::endl; // 5

int threshold = 5;
auto isAboveThreshold = [threshold](int n) { return n > threshold; };
// [threshold] "captures" the outer variable by value

[] (the capture list) controls what from the surrounding scope the lambda can see: [threshold] captures by value (a snapshot at creation time), [&threshold] by reference (sees later changes), and [&]/[=] capture everything used, by reference or by value respectively.

Common mistakes

• Capturing by reference ([&]) and using the lambda after the referenced variable has gone out of scope — this is a dangling reference, exactly like returning a pointer to a local variable in C.