Angle Bracket hack
From cppreference.com
The angle bracket hack resolves a lexing ambiguity when a templated name ending in ">" is used as the template parameter of another class template or function template. Prior to C++11, when two consecutive angle brackets appeared, many lexers would interpret these as the right shift operator instead according to the language grammar. As a workaround, a space would need to be inserted between the two angle brackets so a lexer could interpret them as individual angle bracket tokens.
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template <typename T> struct A { A(){} }; template <typename T> struct B { B(){} }; int main() { A<B<int> > c; // space between >'s needed on many compilers prior to C++11 A<B<int>> d; // ok on C++11 and above }
