YGFloatOptional: Move binary operators to free functions

Summary:
@public

Having binary operators as member functions has disadvantages:

- the left hand side cannot be converted to `YGFloatOptional` implicitly (which we need for `YGStyle` refs)
- Operators are not necessarily commutative.

By moving these operators into free functions, and adding overloads for both variants if one operand is `float`, we get these properties.

Reviewed By: SidharthGuglani

Differential Revision: D15078962

fbshipit-source-id: 2e228a2ef90a8083c91788caa9eedfd4d140677f

yoga/YGFloatOptional.h

@@ -22,25 +22,48 @@ public:
   constexpr float unwrap() const { return value_; }
 
   bool isUndefined() const { return std::isnan(value_); }
-
-  YGFloatOptional operator+(YGFloatOptional op) const {
-    return YGFloatOptional{value_ + op.value_};
-  }
-  bool operator>(YGFloatOptional op) const { return value_ > op.value_; }
-  bool operator<(YGFloatOptional op) const { return value_ < op.value_; }
-  bool operator>=(YGFloatOptional op) const {
-    return *this > op || *this == op;
-  }
-  bool operator<=(YGFloatOptional op) const {
-    return *this < op || *this == op;
-  }
-  bool operator==(YGFloatOptional op) const {
-    return value_ == op.value_ || (isUndefined() && op.isUndefined());
-  }
-  bool operator!=(YGFloatOptional op) const { return !(*this == op); }
-
-  bool operator==(float val) const {
-    return value_ == val || (isUndefined() && yoga::isUndefined(val));
-  }
-  bool operator!=(float val) const { return !(*this == val); }
 };
+
+// operators take YGFloatOptional by value, as it is a 32bit value
+
+inline bool operator==(YGFloatOptional lhs, YGFloatOptional rhs) {
+  return lhs.unwrap() == rhs.unwrap() ||
+      (lhs.isUndefined() && rhs.isUndefined());
+}
+inline bool operator!=(YGFloatOptional lhs, YGFloatOptional rhs) {
+  return !(lhs == rhs);
+}
+
+inline bool operator==(YGFloatOptional lhs, float rhs) {
+  return lhs == YGFloatOptional{rhs};
+}
+inline bool operator!=(YGFloatOptional lhs, float rhs) {
+  return !(lhs == rhs);
+}
+
+inline bool operator==(float lhs, YGFloatOptional rhs) {
+  return rhs == lhs;
+}
+inline bool operator!=(float lhs, YGFloatOptional rhs) {
+  return !(lhs == rhs);
+}
+
+inline YGFloatOptional operator+(YGFloatOptional lhs, YGFloatOptional rhs) {
+  return YGFloatOptional{lhs.unwrap() + rhs.unwrap()};
+}
+
+inline bool operator>(YGFloatOptional lhs, YGFloatOptional rhs) {
+  return lhs.unwrap() > rhs.unwrap();
+}
+
+inline bool operator<(YGFloatOptional lhs, YGFloatOptional rhs) {
+  return lhs.unwrap() < rhs.unwrap();
+}
+
+inline bool operator>=(YGFloatOptional lhs, YGFloatOptional rhs) {
+  return lhs > rhs || lhs == rhs;
+}
+
+inline bool operator<=(YGFloatOptional lhs, YGFloatOptional rhs) {
+  return lhs < rhs || lhs == rhs;
+}