Files
react-native/ReactCommon/react/renderer/mounting/ShadowViewMutation.cpp
T
Samuel Susla 5fa6c5a941 Enable modernize-pass-by-value clang tidy rule
Summary:
changelog: [internal]

You can read more about this rule on https://clang.llvm.org/extra/clang-tidy/checks/modernize-pass-by-value.html

# Isn't it wasteful to copy? Isn't reference more efficient?

This rule of thumb is no longer true since C++11 with move semantics. Let's look at some examples.

# Option one

```
class TextHolder
{
public:
   TextBox(std::string const &text) : text_(text) {}
private:
   std::string text_;
};
```

By using reference here, we prevent the caller from using rvalue to and avoiding copy. Regardless of what the caller passes in, copy always happens.

# Option two

```
class TextHolder
{
public:
   TextBox(std::string const &text) : text_(text) {}
   TextBox(std::string &&text) : text_(std::move(text)) {}
private:
   std::string text_;
};
```
Here, we provide two constructors, one for const reference and one for rvalue reference. This gives the caller option to avoid copy. But now we have two constructors, which is not ideal.

# Option three (what we do in this diff)

```
class TextHolder
{
public:
   TextBox(std::string text) : text_(std::move(text)) {}
private:
   std::string text_;
};
```
Here, the caller has option to avoid copy and we only have single constructor.

Reviewed By: fkgozali, JoshuaGross

Differential Revision: D33276841

fbshipit-source-id: 619d5123d2e28937b22874650366629f24f20a63
2021-12-23 07:53:48 -08:00

152 lines
4.6 KiB
C++

/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/
#include "ShadowViewMutation.h"
#include <utility>
namespace facebook {
namespace react {
ShadowViewMutation ShadowViewMutation::CreateMutation(ShadowView shadowView) {
return {
/* .type = */ Create,
/* .parentShadowView = */ {},
/* .oldChildShadowView = */ {},
/* .newChildShadowView = */ shadowView,
/* .index = */ -1,
};
}
ShadowViewMutation ShadowViewMutation::DeleteMutation(ShadowView shadowView) {
return {
/* .type = */ Delete,
/* .parentShadowView = */ {},
/* .oldChildShadowView = */ shadowView,
/* .newChildShadowView = */ {},
/* .index = */ -1,
};
}
ShadowViewMutation ShadowViewMutation::InsertMutation(
ShadowView parentShadowView,
ShadowView childShadowView,
int index) {
return {
/* .type = */ Insert,
/* .parentShadowView = */ parentShadowView,
/* .oldChildShadowView = */ {},
/* .newChildShadowView = */ childShadowView,
/* .index = */ index,
};
}
ShadowViewMutation ShadowViewMutation::RemoveMutation(
ShadowView parentShadowView,
ShadowView childShadowView,
int index) {
return {
/* .type = */ Remove,
/* .parentShadowView = */ parentShadowView,
/* .oldChildShadowView = */ childShadowView,
/* .newChildShadowView = */ {},
/* .index = */ index,
};
}
ShadowViewMutation ShadowViewMutation::UpdateMutation(
ShadowView oldChildShadowView,
ShadowView newChildShadowView) {
return {
/* .type = */ Update,
/* .parentShadowView = */ {},
/* .oldChildShadowView = */ oldChildShadowView,
/* .newChildShadowView = */ newChildShadowView,
/* .index = */ -1,
};
}
bool ShadowViewMutation::mutatedViewIsVirtual() const {
bool viewIsVirtual = false;
#ifdef ANDROID
// Explanation: Even for non-virtual views,
// for "Insert" mutations, oldChildShadowView is always empty.
// for "Remove" mutations, newChildShadowView is always empty.
// Thus, to see if a view is virtual, we need to always check both the old and
// new View.
viewIsVirtual = newChildShadowView.layoutMetrics == EmptyLayoutMetrics &&
oldChildShadowView.layoutMetrics == EmptyLayoutMetrics;
#endif
return viewIsVirtual;
}
ShadowViewMutation::ShadowViewMutation(
Type type,
ShadowView parentShadowView,
ShadowView oldChildShadowView,
ShadowView newChildShadowView,
int index)
: type(type),
parentShadowView(std::move(parentShadowView)),
oldChildShadowView(std::move(oldChildShadowView)),
newChildShadowView(std::move(newChildShadowView)),
index(index) {}
#if RN_DEBUG_STRING_CONVERTIBLE
std::string getDebugName(ShadowViewMutation const &mutation) {
switch (mutation.type) {
case ShadowViewMutation::Create:
return "Create";
case ShadowViewMutation::Delete:
return "Delete";
case ShadowViewMutation::Insert:
return "Insert";
case ShadowViewMutation::Remove:
return "Remove";
case ShadowViewMutation::Update:
return "Update";
}
}
std::vector<DebugStringConvertibleObject> getDebugProps(
ShadowViewMutation const &mutation,
DebugStringConvertibleOptions options) {
return {
mutation.oldChildShadowView.componentHandle
? DebugStringConvertibleObject{"oldChild",
getDebugDescription(
mutation.oldChildShadowView,
options)}
: DebugStringConvertibleObject{},
mutation.newChildShadowView.componentHandle
? DebugStringConvertibleObject{"newChild",
getDebugDescription(
mutation.newChildShadowView,
options)}
: DebugStringConvertibleObject{},
mutation.parentShadowView.componentHandle
? DebugStringConvertibleObject{"parent",
getDebugDescription(
mutation.parentShadowView,
options)}
: DebugStringConvertibleObject{},
mutation.index != -1
? DebugStringConvertibleObject{"index",
getDebugDescription(
mutation.index, options)}
: DebugStringConvertibleObject{},
};
}
#endif
} // namespace react
} // namespace facebook