Operator overloading lets a type define what an operator means for its values. In C#, subtracting two DateTime values invokes DateTime's overloaded subtraction operator and returns a TimeSpan. section 7.1
Elapsed time in a stopwatch
A stopwatch calculates elapsed time with `_stopTime - _startTime`. Although both operands are structs rather than numbers, the overloaded operator computes the difference from their tick counts and constructs a TimeSpan. section 7.1
public static TimeSpan operator -(DateTime d1, DateTime d2) #1 => new TimeSpan(d1.Ticks - d2.Ticks); #2
The operator declaration makes the runtime behavior explicit: subtraction accepts two DateTime values and returns a TimeSpan built from their tick difference. section 7.1
The example also exposes practical testing concerns around time-dependent operators:
- Using DateTime.UtcNow directly forces tests to depend on real elapsed time, making sleep-based tests slow and flaky. section 7.1
