The term product type comes from the number of states:   A single uint8_t has 256 possible states. A union of uint8_t and uint16_t has 256+65536 states. A struct of uint8_t and uint16_t has 256*65536 states.   That means a union is either or and stores nothing of the uint16_t even if the uint8_t only overwrites one byte. A struct has to store all possible uint8_t and uint16_t in combination.   A heterogeneous list (with predefined types) of course is a product type.   -----Ursprüngliche Nachricht----- Von:Muneem via Std-Proposals <std-proposals_at_[hidden]> Gesendet:Sa 18.04.2026 16:43 Betreff:Re: [std-proposals] Extension to std::tuples to allow runtime indexing. An:std-proposals_at_[hidden]; CC:Muneem <itfllow123_at_[hidden]>; I use terms from wilkipedia since I don't want to be wrong or arrogant enough to think I am always right, but since you are asking me about it: A tuple is a product type, which means it's a type that has lists of objects that can be of any type and nothing else. That's the defintion. Tuples and structs were built to fit just that. Where as my type is meant to not fit that, which means that it can have additional book keeping information.   Sorry for the confusion. I am 17 and new to all this, so I am trying to cite other sources just to stay correct. On Sat, 18 Apr 2026, 7:32 pm Giuseppe D'Angelo via Std-Proposals, <std-proposals_at_[hidden] <mailto:std-proposals_at_[hidden]> > wrote: On 18/04/2026 16:24, Muneem via Std-Proposals wrote: > What I meant, by "tuples have overhead" is that they have a fixed ABI > for all their specaizations, which means that any book keeping has to be > on the top of the tuple and can't be inside it. What does "on top of" or "inside it" mean? Can you show some code? Or even some pseudocode? > Since runtime indexed > tuples are a completely different notion than compile indexed tuple > since one is a product type like a struct. Runtime indexed tuples is > heterogeneous list. Again, I don't understand what any of this means. Please don't use "overloaded" words. People come from all sorts of backgrounds and using these words just causes confusion. Instead please provide the definitions yourself, and add lots of examples to make sure there's no misunderstandings. For instance, what you consider a "heterogeneous list" may not be what other people consider as such. One may understand that as a std::vector<std::any>. My 2 c, -- Giuseppe D'Angelo -- Std-Proposals mailing list Std-Proposals_at_[hidden] <mailto:Std-Proposals_at_[hidden]> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals -- Std-Proposals mailing list Std-Proposals_at_[hidden] https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals