A user-defined literal attaches a suffix to a literal and invokes a literal operator that produces a stronger, specified type. Chrono uses 23h for hours, 34min for minutes, and 1s for seconds instead of constructor syntax such as hours{23}. section 4.2.3
Readable duration syntax
The suffix h calls an operator such as hours operator""h(long long _Val), which returns hours(_Val). Enable the appropriate chrono-literal namespace, for example with using namespace std::literals::chrono_literals. Similar library suffixes support complex numbers with i and strings with s. section 4.2.3
auto nearly_a_day = 23h;
Compare concise literal syntax with constructor syntax when defining a duration. section 4.2.3
