Passing a delegate with two parameters as a parameter function

Question

I have a sequence of functions that look very similar but for a single line, like the following two (but I have many more of them):

private static int HowManyHoursInTheFirstYear(IList<T> samples) {     DateTime firstDate = samples[0].Date;     int count = 0;      while (count < samples.Count &&            samples[count].Date.Year == firstDate.Year)     {         count++;     }      return count; }   private static int HowManyDaysInTheFirstMonth(IList<T> samples) {     DateTime firstDate = samples[0].Date;     int count = 0;      while (count < samples.Count &&             samples[count].Date.Month == firstDate.Month) // <--- only change!         count++;     }      return count; } 

I was thinking about using delegates to remove this repetition in code in some elegant way, that would have allowed me to invoke something like:

HowManyDaysInTheFirstPeriod(     samples,     delegate(DateTime d1, DateTime d2) { return d1.Month == d2.Month; }); 

thereby declaring a delegate like the following:

delegate bool DateComparer(DateTime first, DateTime second); 

and where HowManyDaysInTheFirstPeriod whould be something like the following:

private static int HowManySamplesInFirstPeriod     IList<T> samples,     DateComparer comparer) {     DateTime firstDate = samples[0].Date;     int count = 0;      while (count < samples.Count && comparer())     {         count++;     } } 

Unfortunately, the compiler complains that comparer needs two parameters.

I am relatively new to C# and hit a road-block here. How would you solve this?

Answer 1

You're almost there! The comparer delegate parameter is just like any other function: You still need to pass the appropriate arguments to invoke it. In your case, that's going to mean this change:

while (count < samples.Count && comparer(samples[count].Date, firstDate)) {     count++; } 

(Also, note that samples should probably be samples.Count, as I have written above.)