Why start with std::placeholders::_1 instead of _0?

c++, c++11, placeholder, stdbind

Solution

Because that's how `boost::bind` does it, and the Boost.Bind author wrote the proposal to add it to TR1 and that got copied into the standard.

As for why Boost.Bind does it that way, I don't know, but I would hazard a guess it might be to match `std::bind1st` and `std::bind2nd` from the 1998 standard, which came from the STL. In that context "1st" i.e. "first" is correct (even in a zero-based indexing system the item at index zero is the first, not the zeroth, item.)

So maybe the placeholders should be `_1st`, `_2nd`, `_3rd`, `_4th` etc. but for non-English speakers who don't know the inconsistent suffixes on ordinal numbers it's probably easier to remember `_1`, `_2` etc.

Just a wild guess though. The question had never occurred to me so now I'm curious too :-)

Problem

Original source