I have two for loops in a function which look like these:for (int i=0; i < MAX; ++i) {    identical_lines    identical_lines    identical_lines    first_for_specific_line    identical_lines    identical_lines    identical_lines    first_for_specific_line    identical_lines    identical_lines}for (int i=MAX - 4; i > 0; --i) {    identical_lines    identical_lines    identical_lines    second_for_specific_line    identical_lines    identical_lines    identical_lines    second_for_specific_line    identical_lines    identical_lines}i.e. these two for loops have different conditions and indices, but their code is pretty much the same (all the 'identical_lines' are the same in the two for loops).However there are a few spots (the one marked with 'specific_line') which are different for each one of these for loops.I would like to avoid code duplication and merge these for loops but I can't think of something to unify them and still have the different lines.The language I'm using is C++
Refactoring code with just a few lines different
c++;refactoring
Before grabbing into the modern C++ bag, let us keep things simple and start with some classic, language agnostic techniques. One solution is to make a function of the form   void myfunc(int i,bool upward)   {        identical_lines        identical_lines        identical_lines        if(upward)           first_for_specific_line        else           second_for_specific_line        //...    }and call that like for (int i=0; i < MAX; ++i)    myfunc(i,true);  for (int i=MAX - 4; i > 0; --i)     myfunc(i,false);Note that this is not always the best solution since it has a tendency to make myfunc doing too much, maybe violating the single responsitibility principle. Often it is better to refactor each block you have marked as identical_lines into a small function on its own (lets call it block1(int i), block2(int i) , and create 2 functions   myfunc1(int i)   {        block1(i);        first_for_specific_line;        block2(i);        // ...   }and   myfunc2(int i)   {        block1(i);        second_for_specific_line;        block2(i);        // ...   }and use it like  for (int i=0; i < MAX; ++i)    myfunc1(i);  for (int i=MAX - 4; i > 0; --i)     myfunc2(i);However, to decide what is the best way to cut your code blocks down to small functions depends on what the blocks are really doing. It is better to build abstractions not primarily on formal criteria like the code blocks look similar, but on what is the task or purpose of this block. Ask yourself which of the lines belong together to fulfill that purpose and if you can characterize that task by a single, accurate name.