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author | Indrajith K L | 2022-12-03 17:00:20 +0530 |
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committer | Indrajith K L | 2022-12-03 17:00:20 +0530 |
commit | f5c4671bfbad96bf346bd7e9a21fc4317b4959df (patch) | |
tree | 2764fc62da58f2ba8da7ed341643fc359873142f /v_windows/v/old/vlib/x/json2/README.md | |
download | cli-tools-windows-master.tar.gz cli-tools-windows-master.tar.bz2 cli-tools-windows-master.zip |
Diffstat (limited to 'v_windows/v/old/vlib/x/json2/README.md')
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diff --git a/v_windows/v/old/vlib/x/json2/README.md b/v_windows/v/old/vlib/x/json2/README.md new file mode 100644 index 0000000..fcefbff --- /dev/null +++ b/v_windows/v/old/vlib/x/json2/README.md @@ -0,0 +1,175 @@ +> The name `json2` was chosen to avoid any unwanted potential conflicts with the +> existing codegen tailored for the main `json` module which is powered by CJSON. + +`x.json2` is an experimental JSON parser written from scratch on V. + +## Usage +```v oksyntax +import x.json2 +import net.http + +fn main() { + // Decoding + resp := http.get('https://example.com') ? + + // raw decode + raw_person := json2.raw_decode(resp.text) ? + + // Casting `Any` type / Navigating + person := raw_person.as_map() + name := person['name'].str() // Bob + age := person['age'].int() // 19 + pi := person['pi'].f64() // 3.14.... + + // Constructing an `Any` type + mut me := map[string]json2.Any{} + me['name'] = 'Bob' + me['age'] = 18 + + mut arr := []json2.Any{} + arr << 'rock' + arr << 'papers' + arr << json2.null + arr << 12 + + me['interests'] = arr + + mut pets := map[string]json2.Any{} + pets['Sam'] = 'Maltese Shitzu' + me['pets'] = pets + + // Stringify to JSON + println(me.str()) + //{ + // "name":"Bob", + // "age":18, + // "interests":["rock","papers","scissors",null,12], + // "pets":{"Sam":"Maltese"} + //} + + // Encode a struct/type to JSON + encoded_json := json2.encode<Person>(person2) +} +``` +## Using `decode<T>` and `encode<T>` +> Codegen for this feature is still WIP. +> You need to manually define the methods before using the module to structs. + +In order to use the `decode<T>` and `encode<T>` function, you need to explicitly define +two methods: `from_json` and `to_json`. `from_json` accepts a `json2.Any` argument +and inside of it you need to map the fields you're going to put into the type. +As for `to_json` method, you just need to map the values into `json2.Any` +and turn it into a string. + +```v ignore +struct Person { +mut: + name string + age int = 20 + pets []string +} + +fn (mut p Person) from_json(f json2.Any) { + obj := f.as_map() + for k, v in obj { + match k { + 'name' { p.name = v.str() } + 'age' { p.age = v.int() } + 'pets' { p.pets = v.arr().map(it.str()) } + else {} + } + } +} + +fn (p Person) to_json() string { + mut obj := map[string]json2.Any + obj['name'] = p.name + obj['age'] = p.age + obj['pets'] = p.pets + return obj.str() +} + +fn main() { + resp := os.read_file('./person.json')? + person := json2.decode<Person>(resp)? + println(person) // Person{name: 'Bob', age: 28, pets: ['Floof']} + person_json := json2.encode<Person>(person) + println(person_json) // {"name": "Bob", "age": 28, "pets": ["Floof"]} +} +``` + +## Using struct tags +`x.json2` can access and use the struct field tags similar to the +`json` module by using the comp-time `$for` for structs. + +```v ignore +fn (mut p Person) from_json(f json2.Any) { + mp := an.as_map() + mut js_field_name := '' + $for field in Person.fields { + js_field_name = field.name + + for attr in field.attrs { + if attr.starts_with('json:') { + js_field_name = attr.all_after('json:').trim_left(' ') + break + } + } + + match field.name { + 'name' { p.name = mp[js_field_name].str() } + 'age' { u.age = mp[js_field_name].int() } + 'pets' { u.pets = mp[js_field_name].arr().map(it.str()) } + else {} + } + } +} +``` + +### Null Values +`x.json2` has a separate `null` type for differentiating an undefined value and a null value. +To verify that the field you're accessing is a `null`, use `<typ> is json2.Null`. + +```v ignore +fn (mut p Person) from_json(f json2.Any) { + obj := f.as_map() + if obj['age'] is json2.Null { + // use a default value + p.age = 10 + } +} +``` + +### Custom field names +Aside from using struct tags, you can also just simply cast the base field into a map (`as_map()`) +and access the field you wish to put into the struct/type. + +```v ignore +fn (mut p Person) from_json(f json2.Any) { + obj := f.as_map() + p.name = obj['nickname'].str() +} +``` + +```v oksyntax +fn (mut p Person) to_json() string { + obj := f.as_map() + obj['nickname'] = p.name + return obj.str() +} +``` + +### Undefined Values +Getting undefined values has the same behavior as regular V types. +If you're casting a base field into `map[string]json2.Any` and fetch an undefined entry/value, +it simply returns empty. As for the `[]json2.Any`, it returns an index error. + +## Casting a value to an incompatible type +`x.json2` provides methods for turning `Any` types into usable types. +The following list shows the possible outputs when casting a value to an incompatible type. + +1. Casting non-array values as array (`arr()`) will return an array with the value as the content. +2. Casting non-map values as map (`as_map()`) will return a map with the value as the content. +3. Casting non-string values to string (`str()`) will return the +JSON string representation of the value. +4. Casting non-numeric values to int/float (`int()`/`i64()`/`f32()`/`f64()`) will return zero. |