Meojson

meojson in MaaEnd cpp-algo

meojson is a header-only C++ JSON library, provided via MaaFramework deps. Include via <meojson/json.hpp>.

Core Types

Parsing

#include <meojson/json.hpp>

// From string — returns std::optional<json::value>
auto opt = json::parse(str);
if (!opt) { /* parse failed */ }

// From file
auto opt = json::open("/path/to/file.json");

// JSONC (with comments)
auto opt = json::parsec(str);

cpp-algo 推荐模式 — 安全解析自定义识别参数：

template <typename T>
T ParseCustomRecognitionParam(const char* custom_recognition_param)
{
    if (!custom_recognition_param || std::strlen(custom_recognition_param) == 0) {
        return T {};
    }
    auto opt = json::parse(custom_recognition_param);
    if (!opt) {
        LogError << "failed to parse custom_recognition_param" << VAR(custom_recognition_param);
        return T {};
    }
    T result {};
    if (!result.from_json(*opt)) {
        LogError << "failed to deserialize param" << VAR(custom_recognition_param);
        return T {};
    }
    return result;
}

反模式：json::parse(str).value_or(json::object {}).as<T>() —— value_or 静默吞掉 parse 失败；空 object 调 as<T>() 当 T 有 required 字段时会抛异常。

Constructing Values

json::value v1 = 42;
json::value v2 = "hello";
json::value v3 = true;
json::value v4 = nullptr;    // null

json::array arr { 1, 2, "three" };
json::object obj {
    { "key1", "value1" },
    { "key2", 42 },
};

// From STL containers (implicit conversion)
std::vector<int> vec = {1, 2, 3};
json::value v5 = vec;                              // → JSON array

std::map<std::string, int> m = {{"a", 1}};
json::value v6 = m;                                // → JSON object

Reading Values

Type Checking

v.is_null() / v.is_boolean() / v.is_number() / v.is_string()
v.is_array() / v.is_object()
v.is<int>()     // check if convertible to type

Direct Access (throws on type mismatch)

v.as_string()       // → std::string
v.as_string_view()  // → std::string_view (no copy)
v.as_integer() / v.as_double() / v.as_boolean()
v.as_array()        // → const json::array&
v.as_object()       // → const json::object&
v.as<T>()           // → T (explicit conversion)

Safe Access

// find() returns std::optional<T>
auto opt = v.find<std::string>("key");
if (opt) { std::string s = *opt; }

// get() with default value — supports chained keys
std::string s = v.get("key", "default_value");
int n = v.get("a", "b", 0);  // v["a"]["b"], default 0

// exists() / contains()
if (v.exists("key")) { ... }

Subscript & Iteration

const json::value& v2 = v["key"];      // object access
v["key"] = "new_value";                // mutable (creates key if missing)

for (const auto& item : v.as_array()) { ... }
for (const auto& [key, val] : v.as_object()) { ... }

Serialization

v.dumps()               // compact string
v.dumps(4)              // pretty print with indent=4
v.format()              // same as dumps(4)

cpp-algo 常见模式 — 写回 JSON detail：

template <typename T>
void WriteJsonDetail(MaaStringBuffer* out_detail, const T& payload)
{
    if (out_detail == nullptr) return;
    const std::string json_text = json::value(payload).dumps();
    MaaStringBufferSet(out_detail, json_text.c_str());
}

Object Merge Operator

json::value merged = obj1 | obj2;   // right side wins on conflict
obj1 |= obj2;                       // in-place merge

MEO_JSONIZATION — Struct ↔ JSON

MEO_JSONIZATION(fields...) generates to_json(), check_json(), from_json() member functions.

Basic Usage

struct LocateOutput {
    int status = 0;
    std::string message;
    std::string mapName;
    int x = 0;
    int y = 0;

    MEO_JSONIZATION(status, message, MEO_OPT mapName, MEO_OPT x, MEO_OPT y)
};

// Serialize
json::value j = data;               // implicit via to_json()

// Deserialize — 安全方式：用 from_json() 检查返回值
MyData data {};
if (!data.from_json(j)) {
    LogError << "failed to deserialize" << VAR(j);
}

// as<T>() 在类型不匹配 / required 字段缺失时会抛异常，仅在确定数据合法时使用
MyData data2 = j.as<MyData>();

MEO_OPT — Optional Fields

By default all fields are required in from_json(). Prefix with MEO_OPT to make optional (keeps default if missing):

struct LocateOptions {
    double loc_threshold = 0.55;
    double yolo_threshold = 0.70;
    bool force_global_search = false;

    MEO_JSONIZATION(
        MEO_OPT loc_threshold,
        MEO_OPT yolo_threshold,
        MEO_OPT force_global_search)
};

MEO_KEY — Override JSON Key Name

struct JTemplateMatch {
    std::vector<std::string> template_;   // "template" is C++ keyword
    MEO_TOJSON(MEO_KEY("template") template_);
};

// Combine with MEO_OPT:
MEO_JSONIZATION(MEO_OPT MEO_KEY("default") default_);

Sub-Macros

Supported Field Types

• Primitives: int, double, bool, std::string
• STL containers: std::vector<T>, std::map<std::string, T>, std::array<T,N>
• Nullable: std::optional<T>, std::shared_ptr<T>
• Tuple-like: std::pair<A,B>, std::tuple<...>
• Variant: std::variant<Ts...>
• Nested structs with MEO_JSONIZATION / to_json()
• json::value, json::object, json::array directly

ext::jsonization — Custom Type Support

For types you don't own, specialize json::ext::jsonization<T>:

namespace json::ext {
template <>
class jsonization<cv::Rect> {
public:
    json::value to_json(const cv::Rect& rect) const {
        return json::array { rect.x, rect.y, rect.width, rect.height };
    }
    bool check_json(const json::value& json) const {
        return json.is<std::vector<int>>() && json.as_array().size() == 4;
    }
    bool from_json(const json::value& json, cv::Rect& rect) const {
        auto arr = json.as<std::vector<int>>();
        rect = cv::Rect(arr[0], arr[1], arr[2], arr[3]);
        return true;
    }
};
}

MaaUtils 已提供的特化（通过 <MaaUtils/JsonExt.hpp> 间接可用）：

• cv::Point ↔ [x, y]、cv::Rect ↔ [x, y, w, h]、cv::Size ↔ [w, h]
• std::filesystem::path ↔ UTF-8 string
• std::chrono::milliseconds → "123ms" (to_json only)
• Fallback: any type with operator<< → string (to_json only)

Enum Reflection

enum class MyEnum {
    A, B, C,
    MEOJSON_ENUM_RANGE(A, C)
};

json::value j = MyEnum::B;    // → "B"
MyEnum e = j.as<MyEnum>();    // → MyEnum::B

Common Pitfalls

1. json::parse returns std::optional — always check before use,失败路径必须 LogError + 早期 return
2. as_*() / as<T>() throws on type mismatch — 用 find() 或 is_*() 前置检查；对 struct 用 from_json() 检查返回值
3. 禁止 .value_or(...).as<T>() — 静默吞错误 + 可能抛异常，应拆开检查（见上方推荐模式）
4. char is deleted — use std::string or int
5. ext::jsonization lives in json::ext namespace
6. MEO_OPT applies to the next field only — each optional field needs its own MEO_OPT
7. MEO_KEY goes after MEO_OPT — order is MEO_OPT MEO_KEY("key") field

Quick Reference

For detailed API signatures, see reference.md.