How to give information into a callback function


Hi everyone.

I’m implementing a callback function for lazy constraints (Benders decomposition). I’m not sure if it is possible to give and recover information to the callback. The idea is to pass a global variable which can change its value according to some criteria into the function. So far, It seems like the cb function is not recognizing global variables, declared previously, when I try to use it inside (i.e. the interesting one). I got “ERROR: UndefRefError: access to undefined reference”. Furthermore, when the variable’s value is modified, I don’t know how to recover it. The value of that variable is important at each time when cb function is called.

Is there any way to do that?

Thanks in advance!


Hi @CDRPico, please post a minimum working example that demonstrates what you are trying to do and the error you are getting.

You may also be interested in this Benders decomponsition example.


If the callback needs to have a state, maybe make it a callable struct? Silly Example:

mutable struct Foo

function (foo::Foo)(x)
    r = x+foo.a
    foo.a = x
    return r

Running it:

# constructing the "callback"
julia> f=Foo(1)

# calling it
julia> f(3)

# its state has changed
julia> f