Question

First example:

struct State
{
    SomeLargeObjectThatTakesTimeToCopy obj;
    int x;
} myState;

auto f = [=]() { return myState.x * 2; };

Does the entire myState struct get copied, even though, technically, only the x member is used?

Second example:

struct State
{
    struct SubState
    {
        int x;
    };

    std::vector<SubState> subStates;
} myState;

auto f = [=]() { return myState.subStates[0].x * 2; };

Again, does the entire myState object get copied? If not, then does the entire subStates member get copied?

Answer 1

Assuming myState is a local variable (defined in the body of a function), myState would get captured; lambda can only capture whole variables, not bits and pieces.

If you take your examples as-is, nothing gets captured; lambdas can’t capture global variables.