C++ vector::clear

Question

vector  decoy;

void clear_decoy() {  

    decoy.clear();   

    vector (decoy).swap(decoy);  
}

In the above method

Answer 1

I've never seen that form before.

I have seen it written as:

vector().swap(decoy);

Which means "create a new empty vector, and swap it with the existing one.

vector (decoy).swap(decoy);

To understand that, break in to parts.

vector(decoy) create a new vector (with it's contents copied from the now empty decoy). The new vector is an anonomous temporary, so let's pretent it's name is newvector.

newVector.swap(decoy); swaps the new vector with decopy.

(Updated per comments to fix bug)