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-rw-r--r--modules/skjson/include/SkJSON.h279
1 files changed, 30 insertions, 249 deletions
diff --git a/modules/skjson/include/SkJSON.h b/modules/skjson/include/SkJSON.h
index 8e4231e7a7..4cb312c64f 100644
--- a/modules/skjson/include/SkJSON.h
+++ b/modules/skjson/include/SkJSON.h
@@ -11,7 +11,6 @@
#include "SkArenaAlloc.h"
#include "SkTypes.h"
-class SkString;
class SkWStream;
namespace skjson {
@@ -28,26 +27,12 @@ namespace skjson {
*
* Values are opaque, fixed-size (64 bits), immutable records.
*
- * They can be converted to facade types for type-specific functionality.
+ * They can be freely converted to any of the facade types for type-specific functionality.
*
- * E.g.:
+ * Note: type checking is lazy/deferred, to facilitate chained property access - e.g.
*
- * if (v.is<ArrayValue>()) {
- * for (const auto& item : v.as<ArrayValue>()) {
- * if (const NumberValue* n = item) {
- * printf("Found number: %f", **n);
- * }
- * }
- * }
- *
- * if (v.is<ObjectValue>()) {
- * const StringValue* id = v.as<ObjectValue>()["id"];
- * if (id) {
- * printf("Found object ID: %s", id->begin());
- * } else {
- * printf("Missing object ID");
- * }
- * }
+ * if (!v.as<ObjectValue>()["foo"].as<ObjectValue>()["bar"].is<NullValue>())
+ * LOG("found v.foo.bar!");
*/
class alignas(8) Value {
public:
@@ -61,7 +46,7 @@ public:
};
/**
- * @return The type of this value.
+ * @return The public type of this record.
*/
Type getType() const;
@@ -69,289 +54,85 @@ public:
* @return True if the record matches the facade type T.
*/
template <typename T>
- bool is() const { return this->getType() == T::kType; }
+ bool is() const { return T::IsType(this->getType()); }
/**
- * Unguarded conversion to facade types.
+ * @return The record cast as facade type T.
*
- * @return The record cast as facade type T&.
+ * Note: this is always safe, as proper typing is enforced in the facade methods.
*/
template <typename T>
const T& as() const {
- SkASSERT(this->is<T>());
- return *reinterpret_cast<const T*>(this);
+ return *reinterpret_cast<const T*>(this->is<T>() ? this : &Value::Null());
}
/**
- * Guarded conversion to facade types.
- *
- * @return The record cast as facade type T*.
+ * @return Null value singleton.
*/
- template <typename T>
- operator const T*() const {
- return this->is<T>() ? &this->as<T>() : nullptr;
- }
-
- /**
- * @return The string representation of this value.
- */
- SkString toString() const;
+ static const Value& Null();
protected:
- /*
- Value implementation notes:
-
- -- fixed 64-bit size
-
- -- 8-byte aligned
-
- -- union of:
-
- bool
- int32
- float
- char[8] (short string storage)
- external payload (tagged) pointer
-
- -- highest 3 bits reserved for type storage
-
- */
- enum class Tag : uint8_t {
- // We picked kShortString == 0 so that tag 0x00 and stored max_size-size (7-7=0)
- // conveniently overlap the '\0' terminator, allowing us to store a 7 character
- // C string inline.
- kShortString = 0b00000000, // inline payload
- kNull = 0b00100000, // no payload
- kBool = 0b01000000, // inline payload
- kInt = 0b01100000, // inline payload
- kFloat = 0b10000000, // inline payload
- kString = 0b10100000, // ptr to external storage
- kArray = 0b11000000, // ptr to external storage
- kObject = 0b11100000, // ptr to external storage
- };
- static constexpr uint8_t kTagMask = 0b11100000;
-
- void init_tagged(Tag);
- void init_tagged_pointer(Tag, void*);
-
- Tag getTag() const {
- return static_cast<Tag>(fData8[kTagOffset] & kTagMask);
- }
-
- // Access the record data as T.
- //
- // This is also used to access the payload for inline records. Since the record type lives in
- // the high bits, sizeof(T) must be less than sizeof(Value) when accessing inline payloads.
- //
- // E.g.
- //
- // uint8_t
- // -----------------------------------------------------------------------
- // | val8 | val8 | val8 | val8 | val8 | val8 | val8 | TYPE|
- // -----------------------------------------------------------------------
- //
- // uint32_t
- // -----------------------------------------------------------------------
- // | val32 | unused | TYPE|
- // -----------------------------------------------------------------------
- //
- // T* (64b)
- // -----------------------------------------------------------------------
- // | T* (kTypeShift bits) |TYPE|
- // -----------------------------------------------------------------------
- //
- template <typename T>
- const T* cast() const {
- static_assert(sizeof (T) <= sizeof(Value), "");
- static_assert(alignof(T) <= alignof(Value), "");
- return reinterpret_cast<const T*>(this);
- }
-
- template <typename T>
- T* cast() { return const_cast<T*>(const_cast<const Value*>(this)->cast<T>()); }
-
- // Access the pointer payload.
- template <typename T>
- const T* ptr() const {
- static_assert(sizeof(uintptr_t) == sizeof(Value) ||
- sizeof(uintptr_t) * 2 == sizeof(Value), "");
-
- return (sizeof(uintptr_t) < sizeof(Value))
- // For 32-bit, pointers are stored unmodified.
- ? *this->cast<const T*>()
- // For 64-bit, we use the high bits of the pointer as tag storage.
- : reinterpret_cast<T*>(*this->cast<uintptr_t>() & kTagPointerMask);
- }
-
-private:
- static constexpr size_t kValueSize = 8;
-
- uint8_t fData8[kValueSize];
-
-#if defined(SK_CPU_LENDIAN)
- static constexpr size_t kTagOffset = kValueSize - 1;
-
- static constexpr uintptr_t kTagPointerMask =
- ~(static_cast<uintptr_t>(kTagMask) << ((sizeof(uintptr_t) - 1) * 8));
-#else
- // The current value layout assumes LE and will take some tweaking for BE.
- static_assert(false, "Big-endian builds are not supported at this time.");
-#endif
+ uint8_t fData8[8];
};
class NullValue final : public Value {
public:
- static constexpr Type kType = Type::kNull;
-
- NullValue();
+ static bool IsType(Value::Type t) { return t == Type::kNull; }
};
-class BoolValue final : public Value {
-public:
- static constexpr Type kType = Type::kBool;
-
- explicit BoolValue(bool);
-
- bool operator *() const {
- SkASSERT(this->getTag() == Tag::kBool);
- return *this->cast<bool>();
- }
-};
-
-class NumberValue final : public Value {
+template <typename T, Value::Type vtype>
+class PrimitiveValue final : public Value {
public:
- static constexpr Type kType = Type::kNumber;
+ static bool IsType(Value::Type t) { return t == vtype; }
- explicit NumberValue(int32_t);
- explicit NumberValue(float);
-
- double operator *() const {
- SkASSERT(this->getTag() == Tag::kInt ||
- this->getTag() == Tag::kFloat);
-
- return this->getTag() == Tag::kInt
- ? static_cast<double>(*this->cast<int32_t>())
- : static_cast<double>(*this->cast<float>());
- }
+ T operator *() const;
};
template <typename T, Value::Type vtype>
class VectorValue : public Value {
public:
- using ValueT = T;
- static constexpr Type kType = vtype;
+ static bool IsType(Value::Type t) { return t == vtype; }
- size_t size() const {
- SkASSERT(this->getType() == kType);
- return *this->ptr<size_t>();
- }
+ size_t size() const;
- const T* begin() const {
- SkASSERT(this->getType() == kType);
- const auto* size_ptr = this->ptr<size_t>();
- return reinterpret_cast<const T*>(size_ptr + 1);
- }
-
- const T* end() const {
- SkASSERT(this->getType() == kType);
- const auto* size_ptr = this->ptr<size_t>();
- return reinterpret_cast<const T*>(size_ptr + 1) + *size_ptr;
- }
+ const T* begin() const;
+ const T* end() const;
const T& operator[](size_t i) const {
- SkASSERT(this->getType() == kType);
- SkASSERT(i < this->size());
-
- return *(this->begin() + i);
+ return (i < this->size()) ? *(this->begin() + i) : T::Null();
}
};
-class ArrayValue final : public VectorValue<Value, Value::Type::kArray> {
-public:
- ArrayValue(const Value* src, size_t size, SkArenaAlloc& alloc);
-};
-
-class StringValue final : public Value {
-public:
- static constexpr Type kType = Type::kString;
-
- StringValue();
- StringValue(const char* src, size_t size, SkArenaAlloc& alloc);
-
- size_t size() const {
- switch (this->getTag()) {
- case Tag::kShortString:
- return kMaxInlineStringSize - SkToSizeT(this->cast<char>()[kMaxInlineStringSize]);
- case Tag::kString:
- return this->cast<VectorValue<char, Value::Type::kString>>()->size();
- default:
- return 0;
- }
- }
-
- const char* begin() const {
- return this->getTag() == Tag::kShortString
- ? this->cast<char>()
- : this->cast<VectorValue<char, Value::Type::kString>>()->begin();
- }
-
- const char* end() const {
- if (this->getTag() == Tag::kShortString) {
- const auto* payload = this->cast<char>();
- return payload + kMaxInlineStringSize - SkToSizeT(payload[kMaxInlineStringSize]);
- }
- return this->cast<VectorValue<char, Value::Type::kString>>()->end();
- }
-
-private:
- static constexpr size_t kMaxInlineStringSize = sizeof(Value) - 1;
-};
+using BoolValue = PrimitiveValue<bool , Value::Type::kBool >;
+using NumberValue = PrimitiveValue<double, Value::Type::kNumber>;
+using StringValue = VectorValue<char , Value::Type::kString>;
+using ArrayValue = VectorValue<Value , Value::Type::kArray >;
struct Member {
StringValue fKey;
Value fValue;
+
+ static const Member& Null();
};
class ObjectValue final : public VectorValue<Member, Value::Type::kObject> {
public:
- ObjectValue(const Member* src, size_t size, SkArenaAlloc& alloc);
-
const Value& operator[](const char*) const;
-
-private:
- // Not particularly interesting - hiding for disambiguation.
- const Member& operator[](size_t i) const = delete;
};
class DOM final : public SkNoncopyable {
public:
explicit DOM(const char*);
- const Value& root() const { return fRoot; }
+ const Value& root() const { return *fRoot; }
void write(SkWStream*) const;
private:
SkArenaAlloc fAlloc;
- Value fRoot;
+ const Value* fRoot;
};
-inline Value::Type Value::getType() const {
- switch (this->getTag()) {
- case Tag::kNull: return Type::kNull;
- case Tag::kBool: return Type::kBool;
- case Tag::kInt: return Type::kNumber;
- case Tag::kFloat: return Type::kNumber;
- case Tag::kShortString: return Type::kString;
- case Tag::kString: return Type::kString;
- case Tag::kArray: return Type::kArray;
- case Tag::kObject: return Type::kObject;
- }
-
- SkASSERT(false); // unreachable
- return Type::kNull;
-}
-
} // namespace skjson
#endif // SkJSON_DEFINED
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