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I don't believe that C++ would have had undecidable grammar if it hadn't aimed for source compatibility with C.

• MaulingMonkey 12y ago
  What rubs me the wrong way is that it's not even C compatible. Trying to compile a C codebase with a C++ compiler is more likely than not going to give me hundreds or thousands of conversion errors thanks to the terser casting requirements. It's a worst of both worlds situation: Neither the ability to use C code as-is nor a clean grammar. I also believe the grammar could have been made much better while maintaining C compatibility. The language design seems more like throwing stuff at the wall and rolling with whatever kind of sticks, than fully exploring the problem space. See the export keyword: implemented once, and then removed as worthless, not even bothering with the step of deprecation, at the recommendation of said implementation.
• pcwalton 12y ago
  The undecidability arises from the way that C's lexer hack for types interacts with the way C++ chose to implement templates. There are other approaches to implementing generics that could have avoided this unfortunate interaction while remaining backwards compatible with C (as C does not have generics).