let myvar = [variables(name: "varName1", label: "varLabel1"),variables(name: "varName2", label: "varLabel2")]
let myFileter = Filter(id: "filterId", name: "filterName", variables: myvar)

let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
let revertedData = try? encoder.encode(myFileter)
let revertedJSON = String(data: revertedData!, encoding: .utf8)!
print(revertedJSON)

Output:
{
    "id" : "filterId",
    "name" : "filterName",
    "variables" : [
    {
    "name" : "varName1",
    "label" : "varLabel1"
    },
    {
    "name" : "varName2",
    "label" : "varLabel2"
    }
    ]
}