CODEWITHSUNDEEP
c++xcode
Luigi D.
Luigi D.

Reputation: 315

Xcode won't compile due to LLVM error

I'm trying to write a C++ program in Xcode. My code seems not to have any issues, but when I try to compile it I get the following error:

Implicit instantiation of undefined template 'std::__1::hash<std::1::pair<unsigned long, unsigned long> >'

This error would apparently be at line 1008 of LLVM's type_traits file. I thought it was some library error, but when I tried to compile a simple Hello World, it worked fine.

Anybody know what I'm missing?

Upvotes: 0

Views: 67

Answers (1)

Richard Hodges
Richard Hodges

Reputation: 69912

There is no std::hash specialisation for std::pair (or std::tuple). It's one of the most ridiculous features of the c++ standard and it cripples the library.

This is probably occurring because you're using a std::pair as a key in an unordered_map.

What you need to do is include boost: <boost/functional/hash.hpp> and declare boost::hash<std::pair<X, Y>> as the 3rd template parameter of your map.

Until std::hash is fixed, it's almost useless.

Upvotes: 2

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