NightOwl888 commented on code in PR #1089:
URL: https://github.com/apache/lucenenet/pull/1089#discussion_r1907235951
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src/Lucene.Net/Support/Text/EncodingExtensions.cs:
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@@ -0,0 +1,51 @@
+using System.Text;
+
+namespace Lucene.Net.Support.Text
+{
+ /*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+ /// <summary>
+ /// Extension methods for <see cref="Encoding"/>.
+ /// </summary>
+ internal static class EncodingExtensions
+ {
+ /// <summary>
+ /// Returns a new <see cref="Encoding"/> instance with the <see
cref="DecoderFallback"/> set to throw
+ /// an exception when an invalid byte sequence is encountered.
+ /// <para />
+ /// This is equivalent to Java's <c>CodingErrorAction.REPORT</c> for
both <c>onMalformedInput</c> and
+ /// <c>onUnmappableCharacter</c> and will throw a <see
cref="DecoderFallbackException"/> when failing
+ /// to decode a string. This exception is equivalent to Java's
<c>CharacterCodingException</c>, which is
+ /// a base exception type for both <c>MalformedInputException</c> and
<c>UnmappableCharacterException</c>.
+ /// Thus, to translate Java code that catches any of those exceptions,
you can catch
+ /// <see cref="DecoderFallbackException"/>.
+ /// </summary>
+ /// <param name="encoding">The encoding to clone and set the fallback
on.</param>
+ /// <returns>A new <see cref="Encoding"/> instance with the fallback
set to throw an exception.</returns>
+ /// <remarks>
+ /// Note that it is necessary to return a new, cloned <see
cref="Encoding"/> instance because
+ /// the <see cref="Encoding.DecoderFallback"/> property is read-only
without cloning.
+ /// </remarks>
+ public static Encoding WithDecoderExceptionFallback(this Encoding
encoding)
+ {
+ Encoding newEncoding = (Encoding)encoding.Clone();
Review Comment:
I like the syntax, but it does a heap allocation every time the extension
method is called. Let's change it to use a `ConcurrentDictionary` as a cache.
```c#
internal static class EncodingExtensions
{
private static readonly ConcurrentDictionary<Encoding, Encoding>
exceptionFallbackCache = new ConcurrentDictionary<Encoding, Encoding>();
public static Encoding WithDecoderExceptionFallback(this Encoding
encoding)
{
return exceptionFallbackCache.GetOrAdd(encoding, e =>
{
Encoding newEncoding = (Encoding)e.Clone();
newEncoding.DecoderFallback = DecoderFallback.ExceptionFallback;
return newEncoding;
});
}
}
```
`GetOrAdd()` isn't atomic so there is a slight chance we will get an extra
instance if 2 threads call it at the same time, but it doesn't affect
correctness and isn't very likely to happen.
According to ChatGPT, the `GetHashCode()` method of `Encoding` is not
particularly well optimized, so it might be worth it to make a key based on the
`CodePage` and `DecoderFallback` setting to avoid that overhead. But it would
need benchmarking to see whether that makes much of a difference.
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