Reland "libutils: Introduce StaticString16""
This time with old branches excluded.
Bug: 138856262
Test: Run unit tests.
Change-Id: Id0bb1d54b71e38244d64f1b684db1fda81de854c
Merged-In: I8da93f2c9b95183e32d4a2ea895f90c449abbe4d
diff --git a/libutils/Android.bp b/libutils/Android.bp
index 8be4dd0..30798dd 100644
--- a/libutils/Android.bp
+++ b/libutils/Android.bp
@@ -205,6 +205,7 @@
"Mutex_test.cpp",
"SharedBuffer_test.cpp",
"String8_test.cpp",
+ "String16_test.cpp",
"StrongPointer_test.cpp",
"Unicode_test.cpp",
"Vector_test.cpp",
diff --git a/libutils/SharedBuffer.cpp b/libutils/SharedBuffer.cpp
index 7910c6e..3e703db 100644
--- a/libutils/SharedBuffer.cpp
+++ b/libutils/SharedBuffer.cpp
@@ -41,6 +41,7 @@
// The following is OK on Android-supported platforms.
sb->mRefs.store(1, std::memory_order_relaxed);
sb->mSize = size;
+ sb->mClientMetadata = 0;
}
return sb;
}
diff --git a/libutils/SharedBuffer.h b/libutils/SharedBuffer.h
index fdf13a9..476c842 100644
--- a/libutils/SharedBuffer.h
+++ b/libutils/SharedBuffer.h
@@ -102,7 +102,12 @@
// Must be sized to preserve correct alignment.
mutable std::atomic<int32_t> mRefs;
size_t mSize;
- uint32_t mReserved[2];
+ uint32_t mReserved;
+public:
+ // mClientMetadata is reserved for client use. It is initialized to 0
+ // and the clients can do whatever they want with it. Note that this is
+ // placed last so that it is adjcent to the buffer allocated.
+ uint32_t mClientMetadata;
};
static_assert(sizeof(SharedBuffer) % 8 == 0
diff --git a/libutils/String16.cpp b/libutils/String16.cpp
index 818b171..5c3cf32 100644
--- a/libutils/String16.cpp
+++ b/libutils/String16.cpp
@@ -24,21 +24,21 @@
namespace android {
+static const StaticString16 emptyString(u"");
static inline char16_t* getEmptyString() {
- static SharedBuffer* gEmptyStringBuf = [] {
- SharedBuffer* buf = SharedBuffer::alloc(sizeof(char16_t));
- char16_t* str = static_cast<char16_t*>(buf->data());
- *str = 0;
- return buf;
- }();
-
- gEmptyStringBuf->acquire();
- return static_cast<char16_t*>(gEmptyStringBuf->data());
+ return const_cast<char16_t*>(emptyString.string());
}
// ---------------------------------------------------------------------------
-static char16_t* allocFromUTF8(const char* u8str, size_t u8len)
+void* String16::alloc(size_t size)
+{
+ SharedBuffer* buf = SharedBuffer::alloc(size);
+ buf->mClientMetadata = kIsSharedBufferAllocated;
+ return buf;
+}
+
+char16_t* String16::allocFromUTF8(const char* u8str, size_t u8len)
{
if (u8len == 0) return getEmptyString();
@@ -49,7 +49,7 @@
return getEmptyString();
}
- SharedBuffer* buf = SharedBuffer::alloc(sizeof(char16_t)*(u16len+1));
+ SharedBuffer* buf = static_cast<SharedBuffer*>(alloc(sizeof(char16_t) * (u16len + 1)));
if (buf) {
u8cur = (const uint8_t*) u8str;
char16_t* u16str = (char16_t*)buf->data();
@@ -66,13 +66,13 @@
return getEmptyString();
}
-static char16_t* allocFromUTF16(const char16_t* u16str, size_t u16len) {
+char16_t* String16::allocFromUTF16(const char16_t* u16str, size_t u16len) {
if (u16len >= SIZE_MAX / sizeof(char16_t)) {
android_errorWriteLog(0x534e4554, "73826242");
abort();
}
- SharedBuffer* buf = SharedBuffer::alloc((u16len + 1) * sizeof(char16_t));
+ SharedBuffer* buf = static_cast<SharedBuffer*>(alloc((u16len + 1) * sizeof(char16_t)));
ALOG_ASSERT(buf, "Unable to allocate shared buffer");
if (buf) {
char16_t* str = (char16_t*)buf->data();
@@ -97,8 +97,8 @@
// having run. In this case we always allocate an empty string. It's less
// efficient than using getEmptyString(), but we assume it's uncommon.
- char16_t* data = static_cast<char16_t*>(
- SharedBuffer::alloc(sizeof(char16_t))->data());
+ SharedBuffer* buf = static_cast<SharedBuffer*>(alloc(sizeof(char16_t)));
+ char16_t* data = static_cast<char16_t*>(buf->data());
data[0] = 0;
mString = data;
}
@@ -106,7 +106,7 @@
String16::String16(const String16& o)
: mString(o.mString)
{
- SharedBuffer::bufferFromData(mString)->acquire();
+ acquire();
}
String16::String16(const String16& o, size_t len, size_t begin)
@@ -136,26 +136,30 @@
String16::~String16()
{
- SharedBuffer::bufferFromData(mString)->release();
+ release();
}
size_t String16::size() const
{
- return SharedBuffer::sizeFromData(mString)/sizeof(char16_t)-1;
+ if (isStaticString()) {
+ return staticStringSize();
+ } else {
+ return SharedBuffer::sizeFromData(mString) / sizeof(char16_t) - 1;
+ }
}
void String16::setTo(const String16& other)
{
- SharedBuffer::bufferFromData(other.mString)->acquire();
- SharedBuffer::bufferFromData(mString)->release();
+ release();
mString = other.mString;
+ acquire();
}
status_t String16::setTo(const String16& other, size_t len, size_t begin)
{
const size_t N = other.size();
if (begin >= N) {
- SharedBuffer::bufferFromData(mString)->release();
+ release();
mString = getEmptyString();
return OK;
}
@@ -184,8 +188,7 @@
abort();
}
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)
- ->editResize((len+1)*sizeof(char16_t));
+ SharedBuffer* buf = static_cast<SharedBuffer*>(editResize((len + 1) * sizeof(char16_t)));
if (buf) {
char16_t* str = (char16_t*)buf->data();
memmove(str, other, len*sizeof(char16_t));
@@ -212,8 +215,8 @@
abort();
}
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)
- ->editResize((myLen+otherLen+1)*sizeof(char16_t));
+ SharedBuffer* buf =
+ static_cast<SharedBuffer*>(editResize((myLen + otherLen + 1) * sizeof(char16_t)));
if (buf) {
char16_t* str = (char16_t*)buf->data();
memcpy(str+myLen, other, (otherLen+1)*sizeof(char16_t));
@@ -238,8 +241,8 @@
abort();
}
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)
- ->editResize((myLen+otherLen+1)*sizeof(char16_t));
+ SharedBuffer* buf =
+ static_cast<SharedBuffer*>(editResize((myLen + otherLen + 1) * sizeof(char16_t)));
if (buf) {
char16_t* str = (char16_t*)buf->data();
memcpy(str+myLen, chrs, otherLen*sizeof(char16_t));
@@ -273,8 +276,8 @@
len, myLen, String8(chrs, len).string());
#endif
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)
- ->editResize((myLen+len+1)*sizeof(char16_t));
+ SharedBuffer* buf =
+ static_cast<SharedBuffer*>(editResize((myLen + len + 1) * sizeof(char16_t)));
if (buf) {
char16_t* str = (char16_t*)buf->data();
if (pos < myLen) {
@@ -338,23 +341,87 @@
return strstr16(mString, chrs) != nullptr;
}
+void* String16::edit() {
+ SharedBuffer* buf;
+ if (isStaticString()) {
+ buf = static_cast<SharedBuffer*>(alloc((size() + 1) * sizeof(char16_t)));
+ if (buf) {
+ buf->acquire();
+ memcpy(buf->data(), mString, (size() + 1) * sizeof(char16_t));
+ }
+ } else {
+ buf = SharedBuffer::bufferFromData(mString)->edit();
+ buf->mClientMetadata = kIsSharedBufferAllocated;
+ }
+ return buf;
+}
+
+void* String16::editResize(size_t newSize) {
+ SharedBuffer* buf;
+ if (isStaticString()) {
+ size_t copySize = (size() + 1) * sizeof(char16_t);
+ if (newSize < copySize) {
+ copySize = newSize;
+ }
+ buf = static_cast<SharedBuffer*>(alloc(newSize));
+ if (buf) {
+ buf->acquire();
+ memcpy(buf->data(), mString, copySize);
+ }
+ } else {
+ buf = SharedBuffer::bufferFromData(mString)->editResize(newSize);
+ buf->mClientMetadata = kIsSharedBufferAllocated;
+ }
+ return buf;
+}
+
+void String16::acquire()
+{
+ if (!isStaticString()) {
+ SharedBuffer::bufferFromData(mString)->acquire();
+ }
+}
+
+void String16::release()
+{
+ if (!isStaticString()) {
+ SharedBuffer::bufferFromData(mString)->release();
+ }
+}
+
+bool String16::isStaticString() const {
+ // See String16.h for notes on the memory layout of String16::StaticData and
+ // SharedBuffer.
+ static_assert(sizeof(SharedBuffer) - offsetof(SharedBuffer, mClientMetadata) == 4);
+ const uint32_t* p = reinterpret_cast<const uint32_t*>(mString);
+ return (*(p - 1) & kIsSharedBufferAllocated) == 0;
+}
+
+size_t String16::staticStringSize() const {
+ // See String16.h for notes on the memory layout of String16::StaticData and
+ // SharedBuffer.
+ static_assert(sizeof(SharedBuffer) - offsetof(SharedBuffer, mClientMetadata) == 4);
+ const uint32_t* p = reinterpret_cast<const uint32_t*>(mString);
+ return static_cast<size_t>(*(p - 1));
+}
+
status_t String16::makeLower()
{
const size_t N = size();
const char16_t* str = string();
- char16_t* edit = nullptr;
+ char16_t* edited = nullptr;
for (size_t i=0; i<N; i++) {
const char16_t v = str[i];
if (v >= 'A' && v <= 'Z') {
- if (!edit) {
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)->edit();
+ if (!edited) {
+ SharedBuffer* buf = static_cast<SharedBuffer*>(edit());
if (!buf) {
return NO_MEMORY;
}
- edit = (char16_t*)buf->data();
- mString = str = edit;
+ edited = (char16_t*)buf->data();
+ mString = str = edited;
}
- edit[i] = tolower((char)v);
+ edited[i] = tolower((char)v);
}
}
return OK;
@@ -364,18 +431,18 @@
{
const size_t N = size();
const char16_t* str = string();
- char16_t* edit = nullptr;
+ char16_t* edited = nullptr;
for (size_t i=0; i<N; i++) {
if (str[i] == replaceThis) {
- if (!edit) {
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)->edit();
+ if (!edited) {
+ SharedBuffer* buf = static_cast<SharedBuffer*>(edit());
if (!buf) {
return NO_MEMORY;
}
- edit = (char16_t*)buf->data();
- mString = str = edit;
+ edited = (char16_t*)buf->data();
+ mString = str = edited;
}
- edit[i] = withThis;
+ edited[i] = withThis;
}
}
return OK;
@@ -385,7 +452,7 @@
{
const size_t N = size();
if (begin >= N) {
- SharedBuffer::bufferFromData(mString)->release();
+ release();
mString = getEmptyString();
return OK;
}
@@ -395,8 +462,7 @@
}
if (begin > 0) {
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)
- ->editResize((N+1)*sizeof(char16_t));
+ SharedBuffer* buf = static_cast<SharedBuffer*>(editResize((N + 1) * sizeof(char16_t)));
if (!buf) {
return NO_MEMORY;
}
@@ -404,8 +470,7 @@
memmove(str, str+begin, (N-begin+1)*sizeof(char16_t));
mString = str;
}
- SharedBuffer* buf = SharedBuffer::bufferFromData(mString)
- ->editResize((len+1)*sizeof(char16_t));
+ SharedBuffer* buf = static_cast<SharedBuffer*>(editResize((len + 1) * sizeof(char16_t)));
if (buf) {
char16_t* str = (char16_t*)buf->data();
str[len] = 0;
diff --git a/libutils/String16_test.cpp b/libutils/String16_test.cpp
new file mode 100644
index 0000000..f1f24c3
--- /dev/null
+++ b/libutils/String16_test.cpp
@@ -0,0 +1,218 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <utils/String16.h>
+#include <utils/String8.h>
+
+#include <gtest/gtest.h>
+
+namespace android {
+
+::testing::AssertionResult Char16_tStringEquals(const char16_t* a, const char16_t* b) {
+ if (strcmp16(a, b) != 0) {
+ return ::testing::AssertionFailure()
+ << "\"" << String8(a).c_str() << "\" not equal to \"" << String8(b).c_str() << "\"";
+ }
+ return ::testing::AssertionSuccess();
+}
+
+#define EXPECT_STR16EQ(a, b) EXPECT_TRUE(Char16_tStringEquals(a, b))
+
+TEST(String16Test, FromChar16_t) {
+ String16 tmp(u"Verify me");
+ EXPECT_STR16EQ(u"Verify me", tmp);
+}
+
+TEST(String16Test, FromChar16_tSized) {
+ String16 tmp(u"Verify me", 7);
+ EXPECT_STR16EQ(u"Verify ", tmp);
+}
+
+TEST(String16Test, FromChar) {
+ String16 tmp("Verify me");
+ EXPECT_STR16EQ(u"Verify me", tmp);
+}
+
+TEST(String16Test, FromCharSized) {
+ String16 tmp("Verify me", 7);
+ EXPECT_STR16EQ(u"Verify ", tmp);
+}
+
+TEST(String16Test, Copy) {
+ String16 tmp("Verify me");
+ String16 another = tmp;
+ EXPECT_STR16EQ(u"Verify me", tmp);
+ EXPECT_STR16EQ(u"Verify me", another);
+}
+
+TEST(String16Test, Move) {
+ String16 tmp("Verify me");
+ String16 another(std::move(tmp));
+ EXPECT_STR16EQ(u"Verify me", another);
+}
+
+TEST(String16Test, Size) {
+ String16 tmp("Verify me");
+ EXPECT_EQ(9U, tmp.size());
+}
+
+TEST(String16Test, setTo) {
+ String16 tmp("Verify me");
+ tmp.setTo(u"New content");
+ EXPECT_EQ(11U, tmp.size());
+ EXPECT_STR16EQ(u"New content", tmp);
+}
+
+TEST(String16Test, Append) {
+ String16 tmp("Verify me");
+ tmp.append(String16("Hello"));
+ EXPECT_EQ(14U, tmp.size());
+ EXPECT_STR16EQ(u"Verify meHello", tmp);
+}
+
+TEST(String16Test, Insert) {
+ String16 tmp("Verify me");
+ tmp.insert(6, u"Insert");
+ EXPECT_EQ(15U, tmp.size());
+ EXPECT_STR16EQ(u"VerifyInsert me", tmp);
+}
+
+TEST(String16Test, Remove) {
+ String16 tmp("Verify me");
+ tmp.remove(2, 6);
+ EXPECT_EQ(2U, tmp.size());
+ EXPECT_STR16EQ(u" m", tmp);
+}
+
+TEST(String16Test, MakeLower) {
+ String16 tmp("Verify Me!");
+ tmp.makeLower();
+ EXPECT_EQ(10U, tmp.size());
+ EXPECT_STR16EQ(u"verify me!", tmp);
+}
+
+TEST(String16Test, ReplaceAll) {
+ String16 tmp("Verify verify Verify");
+ tmp.replaceAll(u'r', u'!');
+ EXPECT_STR16EQ(u"Ve!ify ve!ify Ve!ify", tmp);
+}
+
+TEST(String16Test, Compare) {
+ String16 tmp("Verify me");
+ EXPECT_EQ(String16(u"Verify me"), tmp);
+}
+
+TEST(String16Test, StaticString) {
+ String16 nonStaticString("NonStatic");
+ StaticString16 staticString(u"Static");
+
+ EXPECT_TRUE(staticString.isStaticString());
+ EXPECT_FALSE(nonStaticString.isStaticString());
+}
+
+TEST(String16Test, StaticStringCopy) {
+ StaticString16 tmp(u"Verify me");
+ String16 another = tmp;
+ EXPECT_STR16EQ(u"Verify me", tmp);
+ EXPECT_STR16EQ(u"Verify me", another);
+ EXPECT_TRUE(tmp.isStaticString());
+ EXPECT_TRUE(another.isStaticString());
+}
+
+TEST(String16Test, StaticStringMove) {
+ StaticString16 tmp(u"Verify me");
+ String16 another(std::move(tmp));
+ EXPECT_STR16EQ(u"Verify me", another);
+ EXPECT_TRUE(another.isStaticString());
+}
+
+TEST(String16Test, StaticStringSize) {
+ StaticString16 tmp(u"Verify me");
+ EXPECT_EQ(9U, tmp.size());
+}
+
+TEST(String16Test, StaticStringSetTo) {
+ StaticString16 tmp(u"Verify me");
+ tmp.setTo(u"New content");
+ EXPECT_EQ(11U, tmp.size());
+ EXPECT_STR16EQ(u"New content", tmp);
+ EXPECT_FALSE(tmp.isStaticString());
+}
+
+TEST(String16Test, StaticStringAppend) {
+ StaticString16 tmp(u"Verify me");
+ tmp.append(String16("Hello"));
+ EXPECT_EQ(14U, tmp.size());
+ EXPECT_STR16EQ(u"Verify meHello", tmp);
+ EXPECT_FALSE(tmp.isStaticString());
+}
+
+TEST(String16Test, StaticStringInsert) {
+ StaticString16 tmp(u"Verify me");
+ tmp.insert(6, u"Insert");
+ EXPECT_EQ(15U, tmp.size());
+ EXPECT_STR16EQ(u"VerifyInsert me", tmp);
+ EXPECT_FALSE(tmp.isStaticString());
+}
+
+TEST(String16Test, StaticStringRemove) {
+ StaticString16 tmp(u"Verify me");
+ tmp.remove(2, 6);
+ EXPECT_EQ(2U, tmp.size());
+ EXPECT_STR16EQ(u" m", tmp);
+ EXPECT_FALSE(tmp.isStaticString());
+}
+
+TEST(String16Test, StaticStringMakeLower) {
+ StaticString16 tmp(u"Verify me!");
+ tmp.makeLower();
+ EXPECT_EQ(10U, tmp.size());
+ EXPECT_STR16EQ(u"verify me!", tmp);
+ EXPECT_FALSE(tmp.isStaticString());
+}
+
+TEST(String16Test, StaticStringReplaceAll) {
+ StaticString16 tmp(u"Verify verify Verify");
+ tmp.replaceAll(u'r', u'!');
+ EXPECT_STR16EQ(u"Ve!ify ve!ify Ve!ify", tmp);
+ EXPECT_FALSE(tmp.isStaticString());
+}
+
+TEST(String16Test, StaticStringCompare) {
+ StaticString16 tmp(u"Verify me");
+ EXPECT_EQ(String16(u"Verify me"), tmp);
+}
+
+TEST(String16Test, StringSetToStaticString) {
+ StaticString16 tmp(u"Verify me");
+ String16 another(u"nonstatic");
+ another = tmp;
+ EXPECT_STR16EQ(u"Verify me", tmp);
+ EXPECT_STR16EQ(u"Verify me", another);
+}
+
+TEST(String16Test, StringMoveFromStaticString) {
+ StaticString16 tmp(u"Verify me");
+ String16 another(std::move(tmp));
+ EXPECT_STR16EQ(u"Verify me", another);
+}
+
+TEST(String16Test, EmptyStringIsStatic) {
+ String16 tmp("");
+ EXPECT_TRUE(tmp.isStaticString());
+}
+
+} // namespace android
diff --git a/libutils/include/utils/String16.h b/libutils/include/utils/String16.h
index afbc2ed..adc3e7d 100644
--- a/libutils/include/utils/String16.h
+++ b/libutils/include/utils/String16.h
@@ -37,13 +37,17 @@
class String8;
+template <size_t N>
+class StaticString16;
+
// DO NOT USE: please use std::u16string
//! This is a string holding UTF-16 characters.
class String16
{
public:
- /* use String16(StaticLinkage) if you're statically linking against
+ /*
+ * Use String16(StaticLinkage) if you're statically linking against
* libutils and declaring an empty static String16, e.g.:
*
* static String16 sAStaticEmptyString(String16::kEmptyString);
@@ -123,8 +127,76 @@
inline operator const char16_t*() const;
-private:
- const char16_t* mString;
+ // Static and non-static String16 behave the same for the users, so
+ // this method isn't of much use for the users. It is public for testing.
+ bool isStaticString() const;
+
+ private:
+ /*
+ * A flag indicating the type of underlying buffer.
+ */
+ static constexpr uint32_t kIsSharedBufferAllocated = 0x80000000;
+
+ /*
+ * alloc() returns void* so that SharedBuffer class is not exposed.
+ */
+ static void* alloc(size_t size);
+ static char16_t* allocFromUTF8(const char* u8str, size_t u8len);
+ static char16_t* allocFromUTF16(const char16_t* u16str, size_t u16len);
+
+ /*
+ * edit() and editResize() return void* so that SharedBuffer class
+ * is not exposed.
+ */
+ void* edit();
+ void* editResize(size_t new_size);
+
+ void acquire();
+ void release();
+
+ size_t staticStringSize() const;
+
+ const char16_t* mString;
+
+protected:
+ /*
+ * Data structure used to allocate static storage for static String16.
+ *
+ * Note that this data structure and SharedBuffer are used interchangably
+ * as the underlying data structure for a String16. Therefore, the layout
+ * of this data structure must match the part in SharedBuffer that is
+ * visible to String16.
+ */
+ template <size_t N>
+ struct StaticData {
+ // The high bit of 'size' is used as a flag.
+ static_assert(N - 1 < kIsSharedBufferAllocated, "StaticString16 too long!");
+ constexpr StaticData() : size(N - 1), data{0} {}
+ const uint32_t size;
+ char16_t data[N];
+
+ constexpr StaticData(const StaticData<N>&) = default;
+ };
+
+ /*
+ * Helper function for constructing a StaticData object.
+ */
+ template <size_t N>
+ static constexpr const StaticData<N> makeStaticData(const char16_t (&s)[N]) {
+ StaticData<N> r;
+ // The 'size' field is at the same location where mClientMetadata would
+ // be for a SharedBuffer. We do NOT set kIsSharedBufferAllocated flag
+ // here.
+ for (size_t i = 0; i < N - 1; ++i) r.data[i] = s[i];
+ return r;
+ }
+
+ template <size_t N>
+ explicit constexpr String16(const StaticData<N>& s) : mString(s.data) {}
+
+public:
+ template <size_t N>
+ explicit constexpr String16(const StaticString16<N>& s) : mString(s.mString) {}
};
// String16 can be trivially moved using memcpy() because moving does not
@@ -132,6 +204,42 @@
ANDROID_TRIVIAL_MOVE_TRAIT(String16)
// ---------------------------------------------------------------------------
+
+/*
+ * A StaticString16 object is a specialized String16 object. Instead of holding
+ * the string data in a ref counted SharedBuffer object, it holds data in a
+ * buffer within StaticString16 itself. Note that this buffer is NOT ref
+ * counted and is assumed to be available for as long as there is at least a
+ * String16 object using it. Therefore, one must be extra careful to NEVER
+ * assign a StaticString16 to a String16 that outlives the StaticString16
+ * object.
+ *
+ * THE SAFEST APPROACH IS TO USE StaticString16 ONLY AS GLOBAL VARIABLES.
+ *
+ * A StaticString16 SHOULD NEVER APPEAR IN APIs. USE String16 INSTEAD.
+ */
+template <size_t N>
+class StaticString16 : public String16 {
+public:
+ constexpr StaticString16(const char16_t (&s)[N]) : String16(mData), mData(makeStaticData(s)) {}
+
+ constexpr StaticString16(const StaticString16<N>& other)
+ : String16(mData), mData(other.mData) {}
+
+ constexpr StaticString16(const StaticString16<N>&&) = delete;
+
+ // There is no reason why one would want to 'new' a StaticString16. Delete
+ // it to discourage misuse.
+ static void* operator new(std::size_t) = delete;
+
+private:
+ const StaticData<N> mData;
+};
+
+template <typename F>
+StaticString16(const F&)->StaticString16<sizeof(F) / sizeof(char16_t)>;
+
+// ---------------------------------------------------------------------------
// No user servicable parts below.
inline int compare_type(const String16& lhs, const String16& rhs)