bchavez/Bogus · error · ArgumentOutOfRangeException

The parameter is and the calculated set of enums has a…

Error message

The {nameof(count)} parameter is {count} and the calculated set of enums has a length of {enums.Length}. It is impossible to pick {count} enums from a list of {enums.Length}.

What it means

Thrown by Randomizer.EnumValues<T> (note: ArgumentOutOfRangeException) when count is greater than the available enums after exclusion, or count is negative. The available set is computed from Enum.GetValues(T).Except(exclude), so exclusions shrink the pool.

Solutions

Compute the available pool first and clamp count: count = Math.Min(count, pool.Length).
Ensure count >= 0 and <= number of non-excluded enum values.
Pass null for count to let Bogus pick a random amount.

Example fix

// before
var vals = f.Random.EnumValues<MyEnum>(count: 10);
// after
int pool = Enum.GetValues<MyEnum>().Length;
var vals = f.Random.EnumValues<MyEnum>(count: Math.Min(10, pool));

Defensive patterns

Strategy: validation

Validate before calling

static T[] SafeEnumValues<T>(Bogus.Randomizer r, int? count, params T[] exclude) where T : struct, Enum {
    int pool = System.Enum.GetValues<T>().Except(exclude).Count();
    int? safe = count is int c ? Math.Clamp(c, 0, pool) : null;
    return r.EnumValues(safe, exclude);
}

Try / catch

try { return r.EnumValues(count, exclude); }
catch (ArgumentOutOfRangeException ex) when (ex.Message.Contains("impossible to pick")) {
    return r.EnumValues(null, exclude); // let Bogus pick a random count
}

Prevention

Clamp count to the non-excluded enum size.
Pass null for count when a random amount is acceptable.
Compute exclude-aware pool size before requesting count.

When it happens

Trigger: Calling f.Random.EnumValues(count: 10) on an enum with only 3 members, or EnumValues(-1, ...), or excluding members so count > remaining length.

Common situations: Hardcoding a count larger than the enum size; computing count from unrelated config; excluding members then requesting more than remain.

Related errors

AI-assisted analysis of bchavez/Bogus@6ece18c5c2 (2026-08-13). Data as JSON: /api/errors/e5f637ba3185d113. Report an issue: GitHub.

Appendix: source

Thrown at Source/Bogus/Randomizer.cs:706

      T[] enums;
      if( exclude.Length > 0)
      {
         enums = System.Enum.GetValues(typeof(T))
            .OfType<T>()
            .Except(exclude)
            .ToArray();
      }
      else
      {
         enums = System.Enum.GetValues(typeof(T))
            .OfType<T>()
            .Except(exclude)
            .ToArray();
      }

      if( count > enums.Length || count < 0 )
      {
         throw new ArgumentOutOfRangeException(nameof(count), count,
         $"The {nameof(count)} parameter is {count} and the calculated set of enums has a length of {enums.Length}. It is impossible to pick {count} enums from a list of {enums.Length}.");
      }

      return this.ArrayElements(enums, count);
   }

   /// <summary>
   /// Shuffles an IEnumerable source.
   /// </summary>
   public IEnumerable<T> Shuffle<T>(IEnumerable<T> source)
   {
      List<T> buffer = source.ToList();
      for( var i = 0; i < buffer.Count; i++ )
      {
         int j;
         //lock any seed access, for thread safety.
         lock( Locker.Value )
         {

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