Cleanup: pass EqualityOptions as const&

This exposes a useless assignment of export_differing_subtitles,
which I've removed (and altered the comment accordingly).

45 files changed, 45 insertions, 46 deletions

diff --git a/src/asset.cc b/src/asset.cc
index 330bd653..abf9c9c8 100644
--- a/src/asset.cc
+++ b/src/asset.cc
@@ -143,7 +143,7 @@ Asset::hash (function<void (float)> progress) const
 
 
 bool
-Asset::equals(std::shared_ptr<const Asset> other, EqualityOptions opt, NoteHandler note) const
+Asset::equals(std::shared_ptr<const Asset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (_hash != other->_hash) {
 		if (!opt.asset_hashes_can_differ) {
diff --git a/src/asset.h b/src/asset.h
index 9f299acc..b88b1167 100644
--- a/src/asset.h
+++ b/src/asset.h
@@ -88,7 +88,7 @@ public:
 
 	virtual bool equals (
 		std::shared_ptr<const Asset> other,
-		EqualityOptions opt,
+		EqualityOptions const& opt,
 		NoteHandler note
 		) const;
 
diff --git a/src/cpl.cc b/src/cpl.cc
index 86b738d9..f1f01b42 100644
--- a/src/cpl.cc
+++ b/src/cpl.cc
@@ -608,7 +608,7 @@ CPL::reel_file_assets () const
 
 
 bool
-CPL::equals (shared_ptr<const Asset> other, EqualityOptions opt, NoteHandler note) const
+CPL::equals(shared_ptr<const Asset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	auto other_cpl = dynamic_pointer_cast<const CPL>(other);
 	if (!other_cpl) {
diff --git a/src/cpl.h b/src/cpl.h
index 64d08ae9..2a2fc827 100644
--- a/src/cpl.h
+++ b/src/cpl.h
@@ -88,7 +88,7 @@ public:
 
 	bool equals (
 		std::shared_ptr<const Asset> other,
-		EqualityOptions options,
+		EqualityOptions const& options,
 		NoteHandler note
 		) const override;
 
diff --git a/src/dcp.cc b/src/dcp.cc
index 3b267090..7c253a17 100644
--- a/src/dcp.cc
+++ b/src/dcp.cc
@@ -337,7 +337,7 @@ DCP::resolve_refs (vector<shared_ptr<Asset>> assets)
 
 
 bool
-DCP::equals (DCP const & other, EqualityOptions opt, NoteHandler note) const
+DCP::equals(DCP const & other, EqualityOptions const& opt, NoteHandler note) const
 {
 	auto a = cpls ();
 	auto b = other.cpls ();
diff --git a/src/dcp.h b/src/dcp.h
index bf9b3aaf..f4b69615 100644
--- a/src/dcp.h
+++ b/src/dcp.h
@@ -124,7 +124,7 @@ public:
 	 *  @param note Functor to handle notes made by the equality operation.
 	 *  @return true if the DCPs are equal according to EqualityOptions, otherwise false.
 	 */
-	bool equals (DCP const & other, EqualityOptions options, NoteHandler note) const;
+	bool equals(DCP const & other, EqualityOptions const& options, NoteHandler note) const;
 
 	void add (std::shared_ptr<CPL> cpl);
 
diff --git a/src/interop_subtitle_asset.cc b/src/interop_subtitle_asset.cc
index d0c80f5e..e7c1432b 100644
--- a/src/interop_subtitle_asset.cc
+++ b/src/interop_subtitle_asset.cc
@@ -140,7 +140,7 @@ InteropSubtitleAsset::add_font (string load_id, dcp::ArrayData data)
 
 
 bool
-InteropSubtitleAsset::equals (shared_ptr<const Asset> other_asset, EqualityOptions options, NoteHandler note) const
+InteropSubtitleAsset::equals(shared_ptr<const Asset> other_asset, EqualityOptions const& options, NoteHandler note) const
 {
 	if (!SubtitleAsset::equals (other_asset, options, note)) {
 		return false;
diff --git a/src/interop_subtitle_asset.h b/src/interop_subtitle_asset.h
index 3005c8fc..f63740d5 100644
--- a/src/interop_subtitle_asset.h
+++ b/src/interop_subtitle_asset.h
@@ -65,7 +65,7 @@ public:
 
 	bool equals (
 		std::shared_ptr<const Asset>,
-		EqualityOptions,
+		EqualityOptions const&,
 		NoteHandler note
 		) const override;
 
diff --git a/src/mono_picture_asset.cc b/src/mono_picture_asset.cc
index cdfcb0df..b58a5d89 100644
--- a/src/mono_picture_asset.cc
+++ b/src/mono_picture_asset.cc
@@ -101,7 +101,7 @@ storing_note_handler (list<pair<NoteType, string>>& notes, NoteType t, string s)
 
 
 bool
-MonoPictureAsset::equals (shared_ptr<const Asset> other, EqualityOptions opt, NoteHandler note) const
+MonoPictureAsset::equals(shared_ptr<const Asset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (!dynamic_pointer_cast<const MonoPictureAsset>(other)) {
 		return false;
diff --git a/src/mono_picture_asset.h b/src/mono_picture_asset.h
index 625d6ac8..b318d0ad 100644
--- a/src/mono_picture_asset.h
+++ b/src/mono_picture_asset.h
@@ -79,7 +79,7 @@ public:
 
 	bool equals (
 		std::shared_ptr<const Asset> other,
-		EqualityOptions opt,
+		EqualityOptions const& opt,
 		NoteHandler note
 		) const override;
 
diff --git a/src/picture_asset.cc b/src/picture_asset.cc
index f77ce820..56f383e0 100644
--- a/src/picture_asset.cc
+++ b/src/picture_asset.cc
@@ -137,7 +137,7 @@ PictureAsset::descriptor_equals (
 
 bool
 PictureAsset::frame_buffer_equals (
-	int frame, EqualityOptions opt, NoteHandler note,
+	int frame, EqualityOptions const& opt, NoteHandler note,
 	uint8_t const * data_A, unsigned int size_A, uint8_t const * data_B, unsigned int size_B
 	) const
 {
diff --git a/src/picture_asset.h b/src/picture_asset.h
index 236eca22..d9f30ece 100644
--- a/src/picture_asset.h
+++ b/src/picture_asset.h
@@ -122,7 +122,7 @@ protected:
 	friend class StereoPictureAssetWriter;
 
 	bool frame_buffer_equals (
-		int frame, EqualityOptions opt, NoteHandler note,
+		int frame, EqualityOptions const& opt, NoteHandler note,
 		uint8_t const * data_A, unsigned int size_A, uint8_t const * data_B, unsigned int size_B
 		) const;
 
diff --git a/src/reel.cc b/src/reel.cc
index 49fe0360..454028cd 100644
--- a/src/reel.cc
+++ b/src/reel.cc
@@ -179,7 +179,7 @@ Reel::write_to_cpl (xmlpp::Element* node, Standard standard) const
 
 
 bool
-Reel::equals (std::shared_ptr<const Reel> other, EqualityOptions opt, NoteHandler note) const
+Reel::equals(std::shared_ptr<const Reel> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if ((_main_picture && !other->_main_picture) || (!_main_picture && other->_main_picture)) {
 		note (NoteType::ERROR, "Reel: picture assets differ");
diff --git a/src/reel.h b/src/reel.h
index 60b5a64b..d011ec4b 100644
--- a/src/reel.h
+++ b/src/reel.h
@@ -133,7 +133,7 @@ public:
 	bool any_encrypted () const;
 	bool all_encrypted () const;
 
-	bool equals (std::shared_ptr<const Reel> other, EqualityOptions opt, NoteHandler notes) const;
+	bool equals(std::shared_ptr<const Reel> other, EqualityOptions const& opt, NoteHandler notes) const;
 
 	void add (DecryptedKDM const &);
 
diff --git a/src/reel_asset.cc b/src/reel_asset.cc
index 6b0cd4d5..5b8f3126 100644
--- a/src/reel_asset.cc
+++ b/src/reel_asset.cc
@@ -135,7 +135,7 @@ optional_to_string (optional<T> o)
 
 
 bool
-ReelAsset::asset_equals (shared_ptr<const ReelAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelAsset::asset_equals(shared_ptr<const ReelAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	auto const node = cpl_node_name(Standard::SMPTE);
 
diff --git a/src/reel_asset.h b/src/reel_asset.h
index 6de7f1be..e928cb18 100644
--- a/src/reel_asset.h
+++ b/src/reel_asset.h
@@ -132,7 +132,7 @@ public:
 		_annotation_text = boost::none;
 	}
 
-	bool asset_equals (std::shared_ptr<const ReelAsset>, EqualityOptions, NoteHandler) const;
+	bool asset_equals(std::shared_ptr<const ReelAsset>, EqualityOptions const&, NoteHandler) const;
 
 protected:
 
diff --git a/src/reel_atmos_asset.cc b/src/reel_atmos_asset.cc
index fe30cea2..ef39a4eb 100644
--- a/src/reel_atmos_asset.cc
+++ b/src/reel_atmos_asset.cc
@@ -92,7 +92,7 @@ ReelAtmosAsset::write_to_cpl (xmlpp::Node* node, Standard standard) const
 
 
 bool
-ReelAtmosAsset::equals (shared_ptr<const ReelAtmosAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelAtmosAsset::equals(shared_ptr<const ReelAtmosAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (!asset_equals (other, opt, note)) {
 		return false;
diff --git a/src/reel_atmos_asset.h b/src/reel_atmos_asset.h
index 6ceec984..298cbbfd 100644
--- a/src/reel_atmos_asset.h
+++ b/src/reel_atmos_asset.h
@@ -69,7 +69,7 @@ public:
 	}
 
 	xmlpp::Node* write_to_cpl (xmlpp::Node* node, Standard standard) const override;
-	bool equals (std::shared_ptr<const ReelAtmosAsset>, EqualityOptions, NoteHandler) const;
+	bool equals(std::shared_ptr<const ReelAtmosAsset>, EqualityOptions const&, NoteHandler) const;
 
 private:
 	boost::optional<std::string> key_type () const override {
diff --git a/src/reel_closed_caption_asset.cc b/src/reel_closed_caption_asset.cc
index b72a3558..e5649d6a 100644
--- a/src/reel_closed_caption_asset.cc
+++ b/src/reel_closed_caption_asset.cc
@@ -75,7 +75,7 @@ ReelClosedCaptionAsset::ReelClosedCaptionAsset (std::shared_ptr<const cxml::Node
 
 
 bool
-ReelClosedCaptionAsset::equals (shared_ptr<const ReelClosedCaptionAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelClosedCaptionAsset::equals(shared_ptr<const ReelClosedCaptionAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (!asset_equals (other, opt, note)) {
 		return false;
diff --git a/src/reel_closed_caption_asset.h b/src/reel_closed_caption_asset.h
index 00102610..405de34b 100644
--- a/src/reel_closed_caption_asset.h
+++ b/src/reel_closed_caption_asset.h
@@ -70,7 +70,7 @@ public:
 		return asset_of_type<SubtitleAsset>();
 	}
 
-	bool equals (std::shared_ptr<const ReelClosedCaptionAsset>, EqualityOptions, NoteHandler) const;
+	bool equals(std::shared_ptr<const ReelClosedCaptionAsset>, EqualityOptions const&, NoteHandler) const;
 
 	void set_language (dcp::LanguageTag l) {
 		_language = l.to_string();
diff --git a/src/reel_file_asset.cc b/src/reel_file_asset.cc
index dc8ea21f..51b94879 100644
--- a/src/reel_file_asset.cc
+++ b/src/reel_file_asset.cc
@@ -74,7 +74,7 @@ ReelFileAsset::ReelFileAsset (shared_ptr<const cxml::Node> node)
 
 
 bool
-ReelFileAsset::file_asset_equals (shared_ptr<const ReelFileAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelFileAsset::file_asset_equals(shared_ptr<const ReelFileAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (_hash != other->_hash) {
 		if (!opt.reel_hashes_can_differ) {
diff --git a/src/reel_file_asset.h b/src/reel_file_asset.h
index 6ef917ab..687e0d3e 100644
--- a/src/reel_file_asset.h
+++ b/src/reel_file_asset.h
@@ -79,7 +79,7 @@ public:
 		_hash = h;
 	}
 
-	bool file_asset_equals (std::shared_ptr<const ReelFileAsset> other, EqualityOptions opt, NoteHandler note) const;
+	bool file_asset_equals(std::shared_ptr<const ReelFileAsset> other, EqualityOptions const& opt, NoteHandler note) const;
 
 	virtual boost::optional<std::string> key_type () const {
 		return boost::none;
diff --git a/src/reel_markers_asset.cc b/src/reel_markers_asset.cc
index 5a079071..d71a22ec 100644
--- a/src/reel_markers_asset.cc
+++ b/src/reel_markers_asset.cc
@@ -120,7 +120,7 @@ ReelMarkersAsset::write_to_cpl (xmlpp::Node* node, Standard standard) const
 }
 
 bool
-ReelMarkersAsset::equals (shared_ptr<const ReelMarkersAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelMarkersAsset::equals(shared_ptr<const ReelMarkersAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (!asset_equals(other, opt, note)) {
 		return false;
diff --git a/src/reel_markers_asset.h b/src/reel_markers_asset.h
index df87dcce..2a1480a2 100644
--- a/src/reel_markers_asset.h
+++ b/src/reel_markers_asset.h
@@ -52,7 +52,7 @@ public:
 	explicit ReelMarkersAsset (std::shared_ptr<const cxml::Node>);
 
 	xmlpp::Node* write_to_cpl (xmlpp::Node* node, Standard standard) const override;
-	bool equals (std::shared_ptr<const ReelMarkersAsset>, EqualityOptions, NoteHandler) const;
+	bool equals(std::shared_ptr<const ReelMarkersAsset>, EqualityOptions const&, NoteHandler) const;
 
 	void set (Marker, Time);
 	void unset (Marker);
diff --git a/src/reel_picture_asset.cc b/src/reel_picture_asset.cc
index 2e51fec5..eb87d039 100644
--- a/src/reel_picture_asset.cc
+++ b/src/reel_picture_asset.cc
@@ -125,7 +125,7 @@ ReelPictureAsset::write_to_cpl (xmlpp::Node* node, Standard standard) const
 
 
 bool
-ReelPictureAsset::equals (shared_ptr<const ReelPictureAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelPictureAsset::equals(shared_ptr<const ReelPictureAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (!asset_equals (other, opt, note)) {
 		return false;
diff --git a/src/reel_picture_asset.h b/src/reel_picture_asset.h
index 64fa54f4..bf7d40aa 100644
--- a/src/reel_picture_asset.h
+++ b/src/reel_picture_asset.h
@@ -68,7 +68,7 @@ public:
 	}
 
 	virtual xmlpp::Node* write_to_cpl (xmlpp::Node* node, Standard standard) const override;
-	bool equals (std::shared_ptr<const ReelPictureAsset>, EqualityOptions, NoteHandler) const;
+	bool equals(std::shared_ptr<const ReelPictureAsset>, EqualityOptions const&, NoteHandler) const;
 
 	/** @return picture frame rate */
 	Fraction frame_rate () const {
diff --git a/src/reel_sound_asset.cc b/src/reel_sound_asset.cc
index 76495c78..1f2ddcdd 100644
--- a/src/reel_sound_asset.cc
+++ b/src/reel_sound_asset.cc
@@ -82,7 +82,7 @@ ReelSoundAsset::key_type () const
 
 
 bool
-ReelSoundAsset::equals (shared_ptr<const ReelSoundAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelSoundAsset::equals(shared_ptr<const ReelSoundAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (!asset_equals (other, opt, note)) {
 		return false;
diff --git a/src/reel_sound_asset.h b/src/reel_sound_asset.h
index 181bf1d9..16d629d1 100644
--- a/src/reel_sound_asset.h
+++ b/src/reel_sound_asset.h
@@ -65,7 +65,7 @@ public:
 		return asset_of_type<SoundAsset>();
 	}
 
-	bool equals (std::shared_ptr<const ReelSoundAsset>, EqualityOptions, NoteHandler) const;
+	bool equals(std::shared_ptr<const ReelSoundAsset>, EqualityOptions const&, NoteHandler) const;
 
 private:
 	boost::optional<std::string> key_type () const override;
diff --git a/src/reel_subtitle_asset.cc b/src/reel_subtitle_asset.cc
index 04f56788..d856a05e 100644
--- a/src/reel_subtitle_asset.cc
+++ b/src/reel_subtitle_asset.cc
@@ -90,7 +90,7 @@ ReelSubtitleAsset::set_language (dcp::LanguageTag language)
 
 
 bool
-ReelSubtitleAsset::equals (shared_ptr<const ReelSubtitleAsset> other, EqualityOptions opt, NoteHandler note) const
+ReelSubtitleAsset::equals(shared_ptr<const ReelSubtitleAsset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	if (!asset_equals (other, opt, note)) {
 		return false;
diff --git a/src/reel_subtitle_asset.h b/src/reel_subtitle_asset.h
index 95013d34..8b694fd6 100644
--- a/src/reel_subtitle_asset.h
+++ b/src/reel_subtitle_asset.h
@@ -75,7 +75,7 @@ public:
 
 	xmlpp::Node* write_to_cpl (xmlpp::Node* node, Standard standard) const override;
 
-	bool equals (std::shared_ptr<const ReelSubtitleAsset>, EqualityOptions, NoteHandler) const;
+	bool equals(std::shared_ptr<const ReelSubtitleAsset>, EqualityOptions const&, NoteHandler) const;
 
 	void set_language (dcp::LanguageTag language);
 
diff --git a/src/smpte_subtitle_asset.cc b/src/smpte_subtitle_asset.cc
index 3a58ba8e..d5838cd5 100644
--- a/src/smpte_subtitle_asset.cc
+++ b/src/smpte_subtitle_asset.cc
@@ -491,7 +491,7 @@ SMPTESubtitleAsset::write (boost::filesystem::path p) const
 }
 
 bool
-SMPTESubtitleAsset::equals (shared_ptr<const Asset> other_asset, EqualityOptions options, NoteHandler note) const
+SMPTESubtitleAsset::equals(shared_ptr<const Asset> other_asset, EqualityOptions const& options, NoteHandler note) const
 {
 	if (!SubtitleAsset::equals (other_asset, options, note)) {
 		return false;
diff --git a/src/smpte_subtitle_asset.h b/src/smpte_subtitle_asset.h
index 2632e0a5..26144fe1 100644
--- a/src/smpte_subtitle_asset.h
+++ b/src/smpte_subtitle_asset.h
@@ -84,7 +84,7 @@ public:
 
 	bool equals (
 		std::shared_ptr<const Asset>,
-		EqualityOptions,
+		EqualityOptions const&,
 		NoteHandler note
 		) const override;
 
diff --git a/src/sound_asset.cc b/src/sound_asset.cc
index ea952c35..d14d3702 100644
--- a/src/sound_asset.cc
+++ b/src/sound_asset.cc
@@ -130,7 +130,7 @@ SoundAsset::SoundAsset (Fraction edit_rate, int sampling_rate, int channels, Lan
 
 
 bool
-SoundAsset::equals (shared_ptr<const Asset> other, EqualityOptions opt, NoteHandler note) const
+SoundAsset::equals(shared_ptr<const Asset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	ASDCP::PCM::MXFReader reader_A;
 	DCP_ASSERT (file());
diff --git a/src/sound_asset.h b/src/sound_asset.h
index 70c3aee7..125fe94b 100644
--- a/src/sound_asset.h
+++ b/src/sound_asset.h
@@ -99,7 +99,7 @@ public:
 
 	bool equals (
 		std::shared_ptr<const Asset> other,
-		EqualityOptions opt,
+		EqualityOptions const& opt,
 		NoteHandler note
 		) const override;
 
diff --git a/src/stereo_picture_asset.cc b/src/stereo_picture_asset.cc
index cf07c6be..35e39093 100644
--- a/src/stereo_picture_asset.cc
+++ b/src/stereo_picture_asset.cc
@@ -101,7 +101,7 @@ StereoPictureAsset::start_read () const
 
 
 bool
-StereoPictureAsset::equals (shared_ptr<const Asset> other, EqualityOptions opt, NoteHandler note) const
+StereoPictureAsset::equals(shared_ptr<const Asset> other, EqualityOptions const& opt, NoteHandler note) const
 {
 	ASDCP::JP2K::MXFSReader reader_A;
 	DCP_ASSERT (file());
diff --git a/src/stereo_picture_asset.h b/src/stereo_picture_asset.h
index 9c9a2fa1..6ee1d423 100644
--- a/src/stereo_picture_asset.h
+++ b/src/stereo_picture_asset.h
@@ -63,7 +63,7 @@ public:
 
 	bool equals (
 		std::shared_ptr<const Asset> other,
-		EqualityOptions opt,
+		EqualityOptions const& opt,
 		NoteHandler note
 		) const override;
 };
diff --git a/src/subtitle.cc b/src/subtitle.cc
index de3fe03f..65ea9ff5 100644
--- a/src/subtitle.cc
+++ b/src/subtitle.cc
@@ -73,7 +73,7 @@ Subtitle::Subtitle (
 
 
 bool
-Subtitle::equals(shared_ptr<const Subtitle> other, EqualityOptions options, NoteHandler note) const
+Subtitle::equals(shared_ptr<const Subtitle> other, EqualityOptions const& options, NoteHandler note) const
 {
 	bool same = true;
 
diff --git a/src/subtitle.h b/src/subtitle.h
index d42a54b7..5b7a4f13 100644
--- a/src/subtitle.h
+++ b/src/subtitle.h
@@ -125,7 +125,7 @@ public:
 		_fade_down_time = t;
 	}
 
-	virtual bool equals(std::shared_ptr<const dcp::Subtitle> other, EqualityOptions options, NoteHandler note) const;
+	virtual bool equals(std::shared_ptr<const dcp::Subtitle> other, EqualityOptions const& options, NoteHandler note) const;
 
 protected:
 
diff --git a/src/subtitle_asset.cc b/src/subtitle_asset.cc
index 5a448f3f..b7e75419 100644
--- a/src/subtitle_asset.cc
+++ b/src/subtitle_asset.cc
@@ -541,7 +541,7 @@ SubtitleAsset::latest_subtitle_out () const
 
 
 bool
-SubtitleAsset::equals (shared_ptr<const Asset> other_asset, EqualityOptions options, NoteHandler note) const
+SubtitleAsset::equals(shared_ptr<const Asset> other_asset, EqualityOptions const& options, NoteHandler note) const
 {
 	if (!Asset::equals (other_asset, options, note)) {
 		return false;
diff --git a/src/subtitle_asset.h b/src/subtitle_asset.h
index bc5fa882..e1ca5d15 100644
--- a/src/subtitle_asset.h
+++ b/src/subtitle_asset.h
@@ -101,7 +101,7 @@ public:
 
 	bool equals (
 		std::shared_ptr<const Asset>,
-		EqualityOptions,
+		EqualityOptions const&,
 		NoteHandler note
 		) const override;
 
diff --git a/src/subtitle_image.cc b/src/subtitle_image.cc
index 19d7f4eb..f8f8b570 100644
--- a/src/subtitle_image.cc
+++ b/src/subtitle_image.cc
@@ -132,7 +132,7 @@ dcp::operator!= (SubtitleImage const & a, SubtitleImage const & b)
 
 
 bool
-SubtitleImage::equals(shared_ptr<const Subtitle> other_sub, EqualityOptions options, NoteHandler note) const
+SubtitleImage::equals(shared_ptr<const Subtitle> other_sub, EqualityOptions const& options, NoteHandler note) const
 {
 	if (!Subtitle::equals(other_sub, options, note)) {
 		return false;
@@ -158,7 +158,6 @@ SubtitleImage::equals(shared_ptr<const Subtitle> other_sub, EqualityOptions opti
 			} else {
 				other->png_image().write(base + "B.png");
 			}
-			options.export_differing_subtitles = false;
 		}
 		return false;
 	}
diff --git a/src/subtitle_image.h b/src/subtitle_image.h
index 8b1c3521..11fd3915 100644
--- a/src/subtitle_image.h
+++ b/src/subtitle_image.h
@@ -105,7 +105,7 @@ public:
 		return _file;
 	}
 
-	bool equals(std::shared_ptr<const dcp::Subtitle> other_sub, EqualityOptions options, NoteHandler note) const override;
+	bool equals(std::shared_ptr<const dcp::Subtitle> other_sub, EqualityOptions const& options, NoteHandler note) const override;
 
 private:
 	ArrayData _png_image;
diff --git a/src/subtitle_string.cc b/src/subtitle_string.cc
index 91a129da..b627240b 100644
--- a/src/subtitle_string.cc
+++ b/src/subtitle_string.cc
@@ -180,7 +180,7 @@ dcp::operator<< (ostream& s, SubtitleString const & sub)
 
 
 bool
-SubtitleString::equals(shared_ptr<const Subtitle> other_sub, EqualityOptions options, NoteHandler note) const
+SubtitleString::equals(shared_ptr<const Subtitle> other_sub, EqualityOptions const& options, NoteHandler note) const
 {
 	if (!Subtitle::equals(other_sub, options, note)) {
 		return false;
diff --git a/src/subtitle_string.h b/src/subtitle_string.h
index 98ff960b..e59ed7c2 100644
--- a/src/subtitle_string.h
+++ b/src/subtitle_string.h
@@ -191,7 +191,7 @@ public:
 		_effect_colour = c;
 	}
 
-	bool equals(std::shared_ptr<const dcp::Subtitle> other_sub, EqualityOptions options, NoteHandler node) const override;
+	bool equals(std::shared_ptr<const dcp::Subtitle> other_sub, EqualityOptions const& options, NoteHandler node) const override;
 
 private:
 	/** font ID */
diff --git a/src/types.h b/src/types.h
index 947d7e93..c7256d0f 100644
--- a/src/types.h
+++ b/src/types.h
@@ -261,7 +261,7 @@ public:
 	bool issue_dates_can_differ = false;
 	bool load_font_nodes_can_differ = false;
 	bool keep_going = false;
-	/** true to save the first pair of different image subtitles to the current working directory */
+	/** true to save the last pair of different image subtitles to the current working directory */
 	bool export_differing_subtitles = false;
 	/** The maximum allowable absolute difference between the vertical position of subtitles */
 	float max_subtitle_vertical_position_error = 0;