aspnetcore/src/Microsoft.AspNet.Mvc.ModelBinding/Internal/DictionaryHelper.cs

using System;
using System.Collections.Generic;

namespace Microsoft.AspNet.Mvc.ModelBinding.Internal
{
    public static class DictionaryHelper
    {
        public static IEnumerable<KeyValuePair<string, TValue>> FindKeysWithPrefix<TValue>([NotNull] IDictionary<string, TValue> dictionary, 
                                                                                           [NotNull] string prefix)
        {
            TValue exactMatchValue;
            if (dictionary.TryGetValue(prefix, out exactMatchValue))
            {
                yield return new KeyValuePair<string, TValue>(prefix, exactMatchValue);
            }

            foreach (var entry in dictionary)
            {
                var key = entry.Key;

                if (key.Length <= prefix.Length)
                {
                    continue;
                }

                if (!key.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
                {
                    continue;
                }

                // Everything is prefixed by the empty string
                if (prefix.Length == 0)
                {
                    yield return entry;
                }
                else
                {
                    char charAfterPrefix = key[prefix.Length];
                    switch (charAfterPrefix)
                    {
                        case '[':
                        case '.':
                            yield return entry;
                            break;
                    }
                }
            }
        }
    }
}