官术网_书友最值得收藏!

Using the std.json module

JSON is a common data interchange format used on the Web. Phobos has a std.json module that can be used to read and write JSON data. The std.json module is an old module that doesn't take advantage of many of D's advanced features, making it somewhat difficult to use. While newer JSON libraries exist for D, including ones that can be used with syntax and convenience, which is extremely similar to JavaScript itself, Phobos has not yet adopted any of them. Here, we'll read a JSON string, print the current contents, add a new field, and then print out the new JSON.

How to do it…

Suppose we're consuming a web API that returns an array of person objects with a name and ID field. We get the following JSON string from the API:

[{"name":"Alice","id":1},{"name":"Bob","id":2}]

Let's execute the following steps to use the std.json module:

  1. Parse the JSON string.
  2. Loop over the array, getting objects out.
  3. Print the information we need, getting the types out of the web API's specification.
  4. Create the new object.
  5. Append the new object to the list.
  6. Print out the JSON representation.

The code is as follows:

void main() {
    import std.json, std.algorithm, std.stdio;
    auto list = parseJSON(`[{"name":"Alice","id":1},{"name":"Bob","id":2}]);
    foreach(person; list.array.map!(a => a.object)) {
         writeln("ID #", person["id"].integer, " is ", person["name"].str);
    }
    JSONValue newPerson;
    JSONValue[string] obj;
    obj["name"].str = "Charlie";
    obj["id"].integer = 3;
    newPerson.object = obj;
    list.array = list.array ~ newPerson;; // append it to the list
    writeln(toJSON(&list)); // print out the new json
}

It will print the following output:

[{"name":"Alice","id":1},{"name":"Bob","id":2},{"name":"Charlie","id":3}]

How it works…

Phobos' std.json module provides a tagged union to represent a dynamic JSONValue. To use it, you can explicitly check the type with the type property, or simply access the type you need through its str, object, array, integer, and other properties. It will throw an exception if you try to access a property of the wrong type. You can query the current type with the type property.

Array elements in std.json are also JSONValues, which means they need to be accessed through the type properties. That is why we called map on the array. We can't work directly with JSONValue, so mapping it to an object gives something we can immediately use. The map function is a function from std.algorithm that calls the given predicate on each element in the array.

JSONValue properties are either read or write. We cannot modify them in-place. Instead, we read the data or create a temporary file to do our edits then set the finished data back to it.

Finally, toJSON takes a pointer to a root element and returns the JSON string it represents.

See also

主站蜘蛛池模板: 巴马| 杂多县| 抚顺市| 建昌县| 乐山市| 乌海市| 桃源县| 万全县| 房产| 洞头县| 清远市| 平阳县| 海安县| 枝江市| 兴山县| 招远市| 宁远县| 启东市| 望奎县| 巴彦淖尔市| 永靖县| 杂多县| 江北区| 紫金县| 全南县| 乌拉特中旗| 博爱县| 靖安县| 大同县| 巴楚县| 安岳县| 阳泉市| 商丘市| 宜君县| 华容县| 万山特区| 钟祥市| 安宁市| 双柏县| 扎兰屯市| 长垣县|