[core] Use optional to represent possible absence, not empty strings

3 files changed, 16 insertions, 18 deletions

diff --git a/src/mbgl/layout/merge_lines.cpp b/src/mbgl/layout/merge_lines.cpp
index ddae9c2c8d..ce6b5f30d0 100644
--- a/src/mbgl/layout/merge_lines.cpp
+++ b/src/mbgl/layout/merge_lines.cpp
@@ -65,12 +65,12 @@ void mergeLines(std::vector<SymbolFeature> &features) {
         SymbolFeature &feature = features[k];
         GeometryCollection &geometry = feature.geometry;
 
-        if (!feature.label.length()) {
+        if (!feature.label) {
             continue;
         }
 
-        const auto leftKey = getKey(feature.label, geometry, Side::Left);
-        const auto rightKey = getKey(feature.label, geometry, Side::Right);
+        const auto leftKey = getKey(*feature.label, geometry, Side::Left);
+        const auto rightKey = getKey(*feature.label, geometry, Side::Right);
 
         const auto left = rightIndex.find(leftKey);
         const auto right = leftIndex.find(rightKey);
@@ -85,7 +85,7 @@ void mergeLines(std::vector<SymbolFeature> &features) {
 
             leftIndex.erase(leftKey);
             rightIndex.erase(rightKey);
-            rightIndex[getKey(feature.label, features[i].geometry, Side::Right)] = i;
+            rightIndex[getKey(*feature.label, features[i].geometry, Side::Right)] = i;
 
         } else if (left != rightIndex.end()) {
             // found mergeable line adjacent to the start of the current line, merge
diff --git a/src/mbgl/layout/symbol_feature.hpp b/src/mbgl/layout/symbol_feature.hpp
index 3b4eb78d86..fa5af97861 100644
--- a/src/mbgl/layout/symbol_feature.hpp
+++ b/src/mbgl/layout/symbol_feature.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <mbgl/tile/geometry_tile_data.hpp>
+#include <mbgl/util/optional.hpp>
 
 #include <string>
 
@@ -9,8 +10,8 @@ namespace mbgl {
 class SymbolFeature {
 public:
     GeometryCollection geometry;
-    std::u32string label;
-    std::string sprite;
+    optional<std::u32string> label;
+    optional<std::string> sprite;
     std::size_t index;
 };
 
diff --git a/src/mbgl/layout/symbol_layout.cpp b/src/mbgl/layout/symbol_layout.cpp
index 5161d3c34b..84fd9393a2 100644
--- a/src/mbgl/layout/symbol_layout.cpp
+++ b/src/mbgl/layout/symbol_layout.cpp
@@ -91,11 +91,9 @@ SymbolLayout::SymbolLayout(std::string bucketName_,
 
             ft.label = util::utf8_to_utf32::convert(u8string);
 
-            if (!ft.label.empty()) {
-                // Loop through all characters of this text and collect unique codepoints.
-                for (char32_t chr : ft.label) {
-                    ranges.insert(getGlyphRange(chr));
-                }
+            // Loop through all characters of this text and collect unique codepoints.
+            for (char32_t chr : *ft.label) {
+                ranges.insert(getGlyphRange(chr));
             }
         }
 
@@ -103,8 +101,7 @@ SymbolLayout::SymbolLayout(std::string bucketName_,
             ft.sprite = util::replaceTokens(layout.iconImage, getValue);
         }
 
-        if (ft.label.length() || ft.sprite.length()) {
-
+        if (ft.label || ft.sprite) {
             auto &multiline = ft.geometry;
 
             GeometryCollection geometryCollection = feature->getGeometries();
@@ -194,9 +191,9 @@ void SymbolLayout::prepare(uintptr_t tileUID,
         GlyphPositions face;
 
         // if feature has text, shape the text
-        if (feature.label.length()) {
+        if (feature.label) {
             shapedText = glyphSet->getShaping(
-                /* string */ feature.label,
+                /* string */ *feature.label,
                 /* maxWidth: ems */ layout.symbolPlacement != SymbolPlacementType::Line ?
                     layout.textMaxWidth * 24 : 0,
                 /* lineHeight: ems */ layout.textLineHeight * 24,
@@ -208,13 +205,13 @@ void SymbolLayout::prepare(uintptr_t tileUID,
 
             // Add the glyphs we need for this label to the glyph atlas.
             if (shapedText) {
-                glyphAtlas.addGlyphs(tileUID, feature.label, layout.textFont, **glyphSet, face);
+                glyphAtlas.addGlyphs(tileUID, *feature.label, layout.textFont, **glyphSet, face);
             }
         }
 
         // if feature has icon, get sprite atlas position
-        if (feature.sprite.length()) {
-            auto image = spriteAtlas.getImage(feature.sprite, SpritePatternMode::Single);
+        if (feature.sprite) {
+            auto image = spriteAtlas.getImage(*feature.sprite, SpritePatternMode::Single);
             if (image) {
                 shapedIcon = shapeIcon(*image, layout);
                 assert((*image).spriteImage);