Start thread with member function (with inheritance) - c++

Question

So my problem starts pretty much like this question:
Start thread with member function
I have some class Foo, that looks like this:
struct Foo
{
int y;
thread t;
void set(int x){
y = x;
}
void plan(int x){
thread = std::thread ([&]{
set(x);
});
void get(){
if (t.joinable())
t.join();
}
};
Other answers also suggest:
void plan(int x){
thread = std::thread(&Foo::set, this, x);
};
Now, I want to use Foo as a base class for various child class with overloaded set() functions, for exemple:
struct Bar: public Foo
{
void set(int x){
y = x*2;
}
}
My problem is that if done that way, Bar::plan() result in Foo::set() being runned in the new thread instead of Bar::set as expected.
Is there another solution than having to write again the plan() method in every child class of Foo?

Answer 1

You might simply make set virtual:
struct Foo
{
// ...
virtual void set(int x);
};
struct Bar : Foo
{
void set(int x) override;
};

Answer 2

Just mark set as virtual and use the lambda version, being careful to capture everything by value, as the plan invocation may (and probably will) return before the thread actually start to run.
struct Foo
{
int y;
thread t;
virtual void set(int x){
y = x;
}
void plan(int x){
t = std::thread ([this, x]{
this->set(x);
});
}
void get(){
if (t.joinable())
t.join();
}
};
this will call the correct set version even when plan is invoked in a derived class.

Answer 3

Though the answer has been accepted already, Here is a way to do the same using std::bind.
#include <iostream>
#include <thread>
#include <functional>
using namespace std;
struct Foo
{
int y;
thread t;
virtual void set(int x){
y = x;
}
void plan(int x){
t = std::thread (std::bind(&Foo::set, this, x));
}
void get(){
if (t.joinable())
t.join();
}
};
struct Bar: public Foo
{
void set(int x){
cout << "Called" << endl;
y = x*2;
}
};
int main() {
Bar b;
b.plan(2);
b.get();
return 0;
}
Also, Without using lambda, you could have done this also:
void plan(int x){
t = std::thread (&Foo::set, this, x);
}