JSON
Because of the ubiquitous nature of JSON, support for it is built directly into V.
V generates code for JSON encoding and decoding.
No runtime reflection is used. This results in much better performance.
Decoding JSON
import json
struct Foo {
x int
}
struct User {
// Adding a [required] attribute will make decoding fail, if that
// field is not present in the input.
// If a field is not [required], but is missing, it will be assumed
// to have its default value, like 0 for numbers, or '' for strings,
// and decoding will not fail.
name string @[required]
age int
// Use the `skip` attribute to skip certain fields
foo Foo @[skip]
// If the field name is different in JSON, it can be specified
last_name string @[json: lastName]
}
data := '{ "name": "Frodo", "lastName": "Baggins", "age": 25 }'
user := json.decode(User, data) or {
eprintln('Failed to decode json, error: ${err}')
return
}
println(user.name)
println(user.last_name)
println(user.age)
// You can also decode JSON arrays:
sfoos := '[{"x":123},{"x":456}]'
foos := json.decode([]Foo, sfoos)!
println(foos[0].x)
println(foos[1].x)
The json.decode function takes two arguments:
the first is the type into which the JSON value should be decoded and
the second is a string containing the JSON data.
Encoding JSON
import json
struct User {
name string
score i64
}
mut data := map[string]int{}
user := &User{
name: 'Pierre'
score: 1024
}
data['x'] = 42
data['y'] = 360
println(json.encode(data)) // {"x":42,"y":360}
println(json.encode(user)) // {"name":"Pierre","score":1024}
The json module also supports anonymous struct fields, which helps with complex JSON apis with lots
of levels.