How to restructure this code without duplicating too much code? - c++

Question

class
{
public:
void func(const int val, const bool flag)
{
if(flag)
{
while(!lower.empty() && val <= lower.top())
{
// do a bunch of stuff with lower
}
}
else
{
while(!higher.empty() && val >= higher.top())
{
// do a bunch of stuff with higher, but it's the same stuff as would've done
// for lower
}
}
}
private:
std::stack<int> lower;
std::stack<int> higher;
}
I'm trying to figure out a better way to write the clauses because currently, I have a lot of duplicate code in both. The only difference is one clause operates on lower and the other on higher and the <= in the first clause is changed to >= higher in the second one.
I could wrap the clause in a helper function and call it in each clause (and pass in the lower and higher as an argument), e.g.,
class
{
public:
void func(const int val, const bool flag)
{
if(flag)
{
helper(lower, comparer);
}
else
{
helper(lower, comparer);
}
}
void helper(std::stack<int> &st)
{
// do a bunch of stuff with st
}
private:
std::stack<int> lower;
std::stack<int> higher;
}
I'm not sure if this is a good idea and if it is, I'm not sure how to get around the >= vs. <=. I'm hoping for suggestions on my design!

Answer 1

You can do something like the following:
class
{
public:
void func(const int val, const bool flag)
{
std::stack<int> *st;
bool (*compare)(int, int);
if (flag)
{
st = &lower;
compare = [](int a, int b){ return a <= b; };
}
else
{
st = &higher;
compare = [](int a, int b){ return a >= b; };
}
while (!st->empty() && compare(val, st->top()))
{
// do a bunch of stuff with *st
}
}
private:
std::stack<int> lower;
std::stack<int> higher;
}
Alternatively, using a helper would certainly work, too:
class
{
public:
void func(const int val, const bool flag)
{
if (flag)
func_helper(lower, val, std::less_equal{});
else
func_helper(higher, val, std::greater_equal{});
}
private:
std::stack<int> lower;
std::stack<int> higher;
template<typename Comparer>
void func_helper(stack<int> &st, const int val, Comparer compare)
{
while (!st.empty() && compare(val, st.top()))
{
// do a bunch of stuff with st
}
}
}

Answer 2

How about something like this
class
{
public:
void func(const int val, const bool flag)
{
int sign = 1;
std::stack<int>* higher_or_lower = &higher;
if(flag)
{
higher_or_lower = &lower;
sign = -1;
}
while(!higher_or_lower->empty() && sign*val >= sign*higher_or_lower->top())
{
// do a bunch of stuff with higher_or_lower
}
}
private:
std::stack<int> lower;
std::stack<int> higher;
}
The higher_or_lower covers both stacks and the sign takes care of less than vs. greater than.

Answer 3

Or a bit more compact:
class C
{
public:
void func(const int val, const bool flag)
{
const std::stack<int>* st[] = {&lower, &higher};
bool (*compare[])(int, int) = { [](int a, int b) { return a <= b; } , [](int a, int b) { return a >= b; } };
while (!st[flag]->empty() && compare[flag](val, st[flag]->top()))
{
// do a bunch of stuff with *st
}
}
private:
std::stack<int> lower;
std::stack<int> higher;
};