Adding the const there makes gcc very unhappy... 
```
src/base/split.h: In instantiation of ‘TStrm& Base::Join(const TSepType&, const TVal&, const TCb&, TStrm&) [with TSepType = char; TVal = std::vector<std::unique_ptr<Orly::CodeGen::TTest> >; TCb = Orly::CodeGen::TPackage::WriteCc(Orly::CodeGen::TCppPrinter&, const Jhm::TRelPath&) const::<lambda(const std::unique_ptr<const Orly::CodeGen::TTest>&, Orly::CodeGen::TCppPrinter&)>; TStrm = Orly::CodeGen::TCppPrinter]’:
orly/code_gen/package.cc:399:15:   required from here
src/base/split.h:54:17: error: no match for call to ‘(const Orly::CodeGen::TPackage::WriteCc(Orly::CodeGen::TCppPrinter&, const Jhm::TRelPath&) const::<lambda(const std::unique_ptr<const Orly::CodeGen::TTest>&, Orly::CodeGen::TCppPrinter&)>) (const std::unique_ptr<Orly::CodeGen::TTest>&, Orly::CodeGen::TCppPrinter&)’
       cb(it, out);
                 ^
orly/code_gen/package.cc:397:27: note: candidates are:
         Join(',', Tests, [](const std::unique_ptr<const TTest> &test, TCppPrinter &out) {
```