td::size_t(vi)

`td::size_t(vi)` is not a valid expression in C++. It seems like you are trying to convert a variable `vi` to type `td::size_t`. However, `td::size_t` is not a standard C++ type. If you want to convert `vi` to the size type, you can use `std::size_t` which is the correct type for representing sizes in C++. The correct expression would be `static_cast<std::size_t>(vi)`.