当输入在技术上有效但不令人满意时，异常与空结果集

#1 楼

#2 楼

>>> import itertools
>>> input = [1, 2, 3, 4, 5]
>>> list(itertools.combinations(input, 2))
[(1, 2), (1, 3), (1, 4), (1, 5), (2, 3), (2, 4), (2, 5), (3, 4), (3, 5), (4, 5)]
>>> list(itertools.combinations(input, 5))
[(1, 2, 3, 4, 5)]
>>> list(itertools.combinations(input, 6))
[]

>>> list(itertools.combinations(input, -1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: r must be non-negative

#3 楼

#4 楼

#5 楼

#6 楼

#7 楼

#8 楼

 public static class EnumerableExtensions {
   public static IEnumerable<T> ThrowIfEmpty<T>(this IEnumerable<T> input) {
      return input.IfEmpty<T>(() => {
         throw new InvalidOperationException("An enumerable was unexpectedly empty");
      });
   }

   public static IEnumerable<T> IfEmpty<T>(
      this IEnumerable<T> input,
      Action callbackIfEmpty
   ) {
      var enumerator = input.GetEnumerator();
      if (!enumerator.MoveNext()) {
         // Safe because if this throws, we'll never run the return statement below
         callbackIfEmpty();
      }
      return EnumeratePrimedEnumerator(enumerator);
   }

   private static IEnumerable<T> EnumeratePrimedEnumerator<T>(
      IEnumerator<T> primedEnumerator
   ) {
      yield return primedEnumerator.Current;
      while (primedEnumerator.MoveNext()) {
         yield return primedEnumerator.Current;
      }
   }
}
 

 var result = someInputSet
   .CombinationsOf(4, CombinationsGenerationMode.Distinct)
   .ThrowIfEmpty()
   .Select(combo => /* do some operation to a combination */)
   .ToList();
 

 var result = someInputSet
   .CombinationsOf(4, CombinationsGenerationMode.Distinct)
   .IfEmpty(() => _log.Warning(
      $@"Unexpectedly received no results when creating combinations for {
         nameof(someInputSet)}"
   ))
   .Select(combo => /* do some operation to a combination */)
   .ToList();
 

#9 楼

#10 楼

#11 楼

#12 楼

#13 楼

class FemaleClass{

    FemaleStudent GetAnyFemale(){
        var femaleSet= mySet.Select( x=> x.IsFemale());
        if(femaleSet.IsEmpty())
            throw new Exception("No female students");
        else
            return femaleSet.Any();
    }
}

List SomeMethod( Set someInputSet){
    var result = someInputSet
        .CombinationsOf(4, CombinationsGenerationMode.Distinct)
        .Select(combo => /* do some operation to a combination */)
        .ToList();

    // the only information here is that set is empty => there are no combinations

    // BEWARE! if 0 here it may be invalid input, but also a empty set
    if(result.Count == 0)  //Add: "&&someInputSet.NotEmpty()"

    // we go a step further, our API require combinations, so
    // this method cannot satisfy the API request, then we throw.
         throw new Exception("you requsted impossible combinations");

    return result;
}