AcmReceiver: Eliminate AcmReceiver::decoders_

webrtc/modules/audio_coding/neteq/decoder_database.h

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 46 matching lines @@
     // Delete the AudioDecoder object, unless it's external. (This means we can
     // always recreate it later if we need it.)
     void DropDecoder() const { decoder_.reset(); }
 
     int SampleRateHz() const {
       const AudioDecoder* decoder = GetDecoder();
       RTC_DCHECK_EQ(1, !!decoder + !!cng_decoder_);
       return decoder ? decoder->SampleRateHz() : cng_decoder_->sample_rate_hz;
     }
 
-    const SdpAudioFormat& GetFormat() const {
-      RTC_DCHECK(audio_format_);
-      return *audio_format_;
+    const SdpAudioFormat* GetFormat() const {
+      return audio_format_ ? &*audio_format_ : nullptr;

[ossu, 2016/09/20 15:30:56]

I don't think we should be able to keep anything in this database that doesn't
have a valid format. My change in: https://codereview.webrtc.org/2355503002/
makes that so, so maybe put this one in after that one?

[kwiberg-webrtc, 2016/09/20 16:30:29]

I agree. We currently do, though, and it isn't a problem for the stuff I change
in this CL (since only external decoders lack SdpAudioFormat, and I don't need
SdpAudioFormat for them).
That's a good change, but I don't think it needs to be a prerequisite for this
CL. You also touch these lines, so whoever lands his CL last will get an
easy-to-fix conflict and can sort it out so that GetFormat returns a const ref
again.

[ossu, 2016/09/21 10:46:10]

Not that it matters enormously, but if so, why don't you just return a reference
to optional here? That's essentially what you're replicating with making it a
pointer. And we've already got the optional just lying around.

[kwiberg-webrtc, 2016/09/21 11:51:57]

Because of the two equivalent return types const Optional<T>& and const T*, the
latter is (1) more well-known, (2) more general, (3) simpler, and (4) shorter.
Yes, returning const Optional<T>& here would be easier to implement and possibly
a tiny bit faster, but I didn't think it was worth it.

[ossu, 2016/09/21 12:00:56]

I'm not sure I agree with you, but I'm also not sure it's worth another pass
through code review for a bit of code it looks like I'll be removing shortly
anyways.

     }
 
     // Returns true if |codec_type| is comfort noise.
     bool IsComfortNoise() const;
 
     // Returns true if |codec_type| is DTMF.
     bool IsDtmf() const;
 
     // Returns true if |codec_type| is RED.
     bool IsRed() const;
@@ skipping 118 matching lines @@
   int active_decoder_type_;
   int active_cng_decoder_type_;
   mutable std::unique_ptr<ComfortNoiseDecoder> active_cng_decoder_;
   rtc::scoped_refptr<AudioDecoderFactory> decoder_factory_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(DecoderDatabase);
 };
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_AUDIO_CODING_NETEQ_DECODER_DATABASE_H_