From 110a382b5954bdab17a4947cc99ab5e776f69606 Mon Sep 17 00:00:00 2001
From: David Aurelio <davidaurelio@fb.com>
Date: Mon, 29 Apr 2019 09:18:57 -0700
Subject: [PATCH] Expose the value type used by `YGStyle` as `ValueRepr`
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Summary:
@public

Adds `YGStyle::ValueRepr` to make code depending on the actual type easier to write.

So far, we have treated `yoga::detail::CompactValue` as an implementation detail, and that’s what it’s supposed to stay.

React Native Fabric has one value conversion overload that depends on that type, though, and used `decltype(YGStyle{}.margin()[0])` until now.
That’s problematic for two reasons:

- we want to constrain the parameter of `operator[](...)` to enum types, making the `0` unsuitable
- we want to return the non-const overload of the operator to return a custom `Ref` type, which is not the type needed by Fabric.

Making the storage type explicit allows to write more forward-compatible code.

Reviewed By: SidharthGuglani

Differential Revision: D15078960

fbshipit-source-id: 932c27ef2f2cdc6ce965b79894268170f0ccdce5
---
 ReactCommon/fabric/components/view/conversions.h | 4 +---
 ReactCommon/yoga/yoga/YGStyle.h                  | 6 +++++-
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/ReactCommon/fabric/components/view/conversions.h b/ReactCommon/fabric/components/view/conversions.h
index 753e2ac7620..c8d9b9a035f 100644
--- a/ReactCommon/fabric/components/view/conversions.h
+++ b/ReactCommon/fabric/components/view/conversions.h
@@ -302,9 +302,7 @@ inline void fromRawValue(const RawValue &value, YGDisplay &result) {
   LOG(FATAL) << "Could not parse YGDisplay:" << stringValue;
 }
 
-inline void fromRawValue(
-    const RawValue &value,
-    decltype(YGStyle{}.margin()[0]) /* type is subject to change */ &result) {
+inline void fromRawValue(const RawValue &value, YGStyle::ValueRepr &result) {
   if (value.hasType<Float>()) {
     result = yogaStyleValueFromFloat((Float)value);
     return;
diff --git a/ReactCommon/yoga/yoga/YGStyle.h b/ReactCommon/yoga/yoga/YGStyle.h
index dd94683224f..953c6ae8f5c 100644
--- a/ReactCommon/yoga/yoga/YGStyle.h
+++ b/ReactCommon/yoga/yoga/YGStyle.h
@@ -7,7 +7,7 @@
 #pragma once
 #include <algorithm>
 #include <array>
-#include <initializer_list>
+#include <type_traits>
 #include "CompactValue.h"
 #include "YGEnums.h"
 #include "YGFloatOptional.h"
@@ -171,6 +171,10 @@ private:
   BITFIELD_ACCESSORS(flexWrap);
   BITFIELD_ACCESSORS(overflow);
   BITFIELD_ACCESSORS(display);
+
+public:
+  // for library users needing a type
+  using ValueRepr = std::remove_reference<decltype(margin_[0])>::type;
 };
 
 bool operator==(const YGStyle& lhs, const YGStyle& rhs);