Mmm, what does L stand for here?
Should we somehow indicate that we assumed that the function returns a success value? I.e., bug visitor / tag.
Also what is the intended behavior if we replace write_into_out_param_on_success with write_into_out_param_on_failure here?
That is, i really want this test added, and then it's good to commit, other nits are minor.
That's super verbose with iterators and requires putting those values in the array.
<template T, template Others...> bool isAnyOf(T Val, Others... OtherVals)