how implement callback from C++ function to Swift - c++

Question

I tried do something in a cpp class and when doing the function return callback to swift.
So i do these things :
Creating this function in callbackClass.cpp
int callback::run(void (*callback)(int))
{
for (unsigned int i = 0; i < 100; i++)
{
callback(i);
}
return 0;
}
In callbackClass.hpp :
class callbackClass.hpp
{
.
.
.
public:
int run(void (*callback)(int));
};
#endif
And for header.h‍‍ :
int callback(void (*callback)(int));
It's good until logging callback in Swift side:
func callbackFunc(){
callback({valueFromCallback in //call cpp function
print(valueFromCallback) //Works fine
})
}
But when try to do other stuff like :
func callbackFunc(){
var value : String!
callback({valueFromCallback in //call cpp function
value = String(valueFromCallback) //It has a problem
})
}
Xcode return this error :
A C function pointer cannot be formed from a closure that captures context
I have already seen these questions but did not help:
Swift: Pass data to a closure that captures context
How to cast self to UnsafeMutablePointer<Void> type in swift
A C function pointer cannot be formed from a closure that captures context

Answer 1

Eventually I realized it possible to pass 'closure' to c++ as argument
So at first I created a Closure in Swift class:
typealias closureCallback = (Int32) -> ()
Then passed it to cpp side :
In header.h‍‍
int callback(void (^closureCallback)(int));
In callbackClass.hpp :
class callbackClass.hpp
{
.
.
.
public:
int run(void (^closureCallback)(int));
};
#endif
And in callbackClass.cpp
int callback::run(void (^closureCallback)(int))
{
for (unsigned int i = 0; i < 100; i++)
{
closureCallback(i);
}
return 0;
}
At last handle it in Swift :
typealias closureCallback = (Int32) -> ()
func callbackFunc(){
var value : String!
let closureValue: closureCallback = {valueFromclosureCallback in
value = String(valueFromclosureCallback)
}
callback(closureValue) //call cpp function
}