CODEWITHSUNDEEP
c++function-pointers
Dmitriy
Dmitriy

Reputation: 77

c++ passing function to function

I've got class funciton Find. This function have to accept some variables and sometimes (pointer to) another function which will be used inside. How I should declare it?

class CRoute
{
...
list<_T> Find(_T u1, _T u2, ????){
   if (????) {...}
}
...
}

have to accept:

X.Find ( "Wien", "Berlin" );
X.Find ( "Wien", "Munchen", TrainFilterCompany ( set<string> { "CD", "DB" } ) );
X.Find ( "Wien", "Munchen", TrainFilterSpeed ( 120, 200 ) );
X.Find ( "Wien", "Munchen", [] ( const CTrain & x ) { return x . m_Company == "CD"; } );

(funtions returns bool)

(_T in this case is string)

Upvotes: 2

Views: 110

Answers (1)

Daniel Schepler
Daniel Schepler

Reputation: 3103

You can define a template method taking any callable object (which would support lambdas with captures as well as passing in a reference to an external function):

template <typename Filter>
list<_T> Find(_T u1, _T u2, Filter filter) {
    if (filter(obj)) ...
}

// Overload taking no filter and returning everything
list<_T> Find(_T u1, _T u2) {
    return Find(u1, u2, [](const CTrain&) -> bool { return true; });
}

You can also use something like std::function<bool (const CTrain&)>. This would incur a slight overhead of a dynamic allocation when passing in a callable object, but it wouldn't result in code explosion if the Find method is particularly complex.

Upvotes: 3

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