Question

I am using dtl-cpp to compare the difference of two files line by line.

I have set up this comparator:

class LBCompareNSString : public dtl::Compare<NSString *> {
public:
  virtual bool impl(const NSString *& A, const NSString *& B) const {
    return [A isEqualToString:B];
  }
};

I have two vectors of NSString objects, like so with the custom comparator:

std::vector<NSString *> linesInACxx;
std::vector<NSString *> linesInBCxx;

And I set up dtl-cpp in this way:

LBCompareNSString comparator;
dtl::Diff< NSString *, std::vector<NSString *>, LBCompareNSString > dtlEngine(linesInACxx, linesInBCxx, comparator);
dtlEngine.compose();

However, when I compile I get this error in Diff.hpp:

Diff.hpp:506: error: no matching function for call to 'LBCompareNSString::impl(NSString*&, NSString*&)'
LBDifferenceEngine.mm:7: note: candidates are: virtual bool LBCompareNSString::impl(const NSString*&, const NSString*&) const

I have no idea how to declare the method so it will work. I tried removing virtual and const but that did not work. Does anyone know what I might have done wrong?

Answer 1

Aha! I found what I’ve done wrong.

virtual bool impl(const NSString *& A, const NSString *& B) const

should be

virtual bool impl(NSString *& A, NSString *& B) const

just like the compiler says.