Question

In C#, is there any significant reduction in memory allocation when passing a DateTime reference as a parameter to a function as opposed to passing it by value?

int GetDayNumber(ref DateTime date)

vs

int GetDayNumber(DateTime date)

The code inside the function is not modifying the date in any case.

Answer 1

A DateTime is a 8 byte struct. A ref has 4 or 8 bytes depending on your target architecture. So at best you’d save 4 bytes of stack memory, which is completely irrelevant.

It’s even likely that ref prevents some optimizations, such as placing the DateTime in a register, thus actually increasing memory use.

This is a clear case of premature optimization. Don’t do this.