CODEWITHSUNDEEP
c++c++11casting
Nick
Nick

Reputation: 10539

What is correct way to deal with ambiguous typecasting/conversions C++11

I have code similar to this:

class Pair{
public:
    Pair(const void *blob);
    //...
    int cmp(const std::string &key) const;
    int cmp(const Pair &pair) const;
}

Later if I do:

Pair p = ...;
p.cmp("Hello");

It won't compile, because conversion from const char * is ambiguous.

It can be translated to std::string and cmp(std::string) to be invoked, or...

it can be translated to Pair and cmp(const Pair) to be invoked.

I can not do constructor explicit.

I tried to do:

Pair(const char *blob) = deleted;

But then I can not construct the class with nullptr and I want to be able to do so.

As final solution, I defined following method:

int cmp(const char *key) const{
   return cmp( std::string{ key } );
}

and it works fine.

Is there better way to deal with such class conversions?

Upvotes: 2

Views: 124

Answers (2)

5gon12eder
5gon12eder

Reputation: 25409

Your “final solution” looks pretty good to me. Not constructing a temporary will also help improve performance. If your strings are known not to contain NUL characters, you can implement the version taking a std::string as argument as

inline int
cmp(const std::string& s)
{
  return this->cmp(s.c_str());
}

which is too simple to worry about.

Making Pair's constructor explicit (I assume the “implicit” is a typo) sounds a good idea to me, too. Why can't you do it?

Upvotes: 4

R Sahu
R Sahu

Reputation: 206577

You can make the constructor explicit.

explicit Pair(const void *blob) { ... }

Then,

p.cmp("Hello");

will resolve to

int cmp(const std::string &key) const;

Upvotes: 2

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