C++ Default capture


Example

By default, local variables that are not explicitly specified in the capture list, cannot be accessed from within the lambda body. However, it is possible to implicitly capture variables named by the lambda body:

int a = 1;
int b = 2;

// Default capture by value
[=]() { return a + b; }; // OK; a and b are captured by value

// Default capture by reference
[&]() { return a + b; }; // OK; a and b are captured by reference

Explicit capturing can still be done alongside implicit default capturing. The explicit capture definition will override the default capture:

int a = 0;
int b = 1;

[=, &b]() {
    a = 2; // Illegal; 'a' is capture by value, and lambda is not 'mutable'
    b = 2; // OK; 'b' is captured by reference
};