cpp core · advanced

Type Erasure & std::function

std::function type-erases any callable of a signature: it stores the callable (small-buffer or heap) plus an ops table, and dispatches through it.

The code

int square(int x);                       // free function
auto lam = [k](int x) { return x * k; }; // lambda (captures k)
struct Mul {
    int operator()(int) const;
}; // functor

std::function<int(int)> f = lam; // type-erased into f
int r = f(5);                    // ops.invoke(storage, 5)
f = square;                      // reassign - same call site

What this lesson walks through

1. 01Any callable of one signature
2. 02Assigning type-erases the callable
3. 03Inside: storage + an ops table
4. 04Small buffer vs heap
5. 05Calling dispatches through invoke
6. 06Reassign — same call site
7. 07Type erasure in one line

std::function<int(int)> can hold any callable matching that signature - a function pointer, a lambda (even with captures), or a functor. Three different concrete types.