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QuickWriteQuickWrite
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Add the JSON parser
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3 files changed

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‎src/main/kotlin/parser/JSONParser.kt

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package net.quickwrite.parser
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import net.quickwrite.lexer.JSONLexeme
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import net.quickwrite.lexer.JSONLexemeType.*
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import net.quickwrite.lexer.StringJSONLexer
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import java.math.BigDecimal
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import java.util.Stack
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private enum class State {
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START,
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OBJECT,
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ARRAY,
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}
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fun jsonParse(input: String): Any? {
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val lexer = StringJSONLexer(input)
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var state = State.START
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var token: JSONLexeme
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var stack = Stack<Any?>()
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while (true) {
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token = lexer.getNext()
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if (token.type == EOF) {
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break
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}
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when(state) {
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State.START -> {
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when(token.type) {
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NULL -> stack.push(null)
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TRUE -> stack.push(true)
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FALSE -> stack.push(false)
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STRING -> stack.push(token.content)
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NUMBER -> stack.push(BigDecimal(token.content!!))
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CURLY_OPEN -> {
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state = State.OBJECT
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stack.push(HashMap<String, Any?>())
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continue
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}
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SQUARE_OPEN -> {
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state = State.ARRAY
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stack.push(ArrayList<Any?>())
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continue
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}
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EOF -> error("Unreachable")
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else -> throw ParserException("Invalid Token") // TODO: Better error reporting
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}
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break
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}
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State.OBJECT -> {
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if(token.type == CURLY_CLOSE) {
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val jsonObject = stack.pop()
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if(stack.empty()){
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stack.push(jsonObject)
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break
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}
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// If this is an object
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if (stack.peek() is String) {
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val name = stack.pop() as String
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(stack.peek() as HashMap<String, Any?>)[name] = jsonObject
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continue
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}
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// Should now be an array
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(stack.peek() as ArrayList<Any?>).add(jsonObject)
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state = State.ARRAY
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continue
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}
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val map = stack.peek() as HashMap<String, Any?>
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if(map.isNotEmpty()) {
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if (token.type != COMMA) {
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throw ParserException("Expected a ',' or a '}', but got ${token.type}") // TODO: Better error reporting
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}
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token = lexer.getNext()
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}
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if (token.type != STRING) {
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throw ParserException("Expected an entry or a '}', but got ${token.type}") // TODO: Better error reporting
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}
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val identifier = token.content!!
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token = lexer.getNext()
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if (token.type != COLON) {
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throw ParserException("Expeced ':' (COLON), but got ${token.type}") // TODO: Better error reporting
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}
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token = lexer.getNext()
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when(token.type) {
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NULL -> map[identifier] = null
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TRUE -> map[identifier] = true
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FALSE -> map[identifier] = false
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STRING -> map[identifier] = token.content
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NUMBER -> map[identifier] = BigDecimal(token.content!!)
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CURLY_OPEN -> {
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stack.push(identifier)
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state = State.OBJECT
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stack.push(HashMap<String, Any?>())
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continue
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}
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SQUARE_OPEN -> {
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stack.push(identifier)
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state = State.ARRAY
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stack.push(ArrayList<Any?>())
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continue
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}
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EOF -> break
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else -> throw ParserException("Invalid Token") // TODO: Better error reporting
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}
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}
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State.ARRAY -> {
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if (token.type == SQUARE_CLOSE) {
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val array = stack.pop()
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if(stack.empty()){
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stack.push(array)
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break
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}
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// If this is an object
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if (stack.peek() is String) {
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val name = stack.pop() as String
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(stack.peek() as HashMap<String, Any?>)[name] = array
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state = State.OBJECT
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continue
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}
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// Should now be an array
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(stack.peek() as ArrayList<Any?>).add(array)
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continue
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}
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val array = stack.peek() as ArrayList<Any?>
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if (array.isNotEmpty()) {
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if (token.type != COMMA) {
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throw ParserException("Expected a ',' or a ']', but got ${token.type}") // TODO: Better error reporting
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}
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token = lexer.getNext()
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}
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when(token.type) {
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NULL -> array.add(null)
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TRUE -> array.add(true)
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FALSE -> array.add(false)
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STRING -> array.add(token.content)
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NUMBER -> array.add(BigDecimal(token.content!!))
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CURLY_OPEN -> {
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state = State.OBJECT
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stack.push(HashMap<String, Any?>())
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continue
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}
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SQUARE_OPEN -> {
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state = State.ARRAY
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stack.push(ArrayList<Any?>())
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continue
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}
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EOF -> break
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else -> throw ParserException("Invalid Token") // TODO: Better error reporting
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}
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}
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}
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}
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if (stack.empty()) {
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throw ParserException("JSON cannot be empty")
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}
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// Too much JSON
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if (lexer.getNext().type != EOF) {
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throw ParserException("Invalid JSON") // TODO: Better error handling
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}
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val result = stack.pop()
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// Too little JSON
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if (!stack.empty()) {
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throw ParserException("Invalid JSON") // TODO: Better error handling
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}
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return result
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}

‎src/main/kotlin/parser/ParserException.kt

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package net.quickwrite.parser
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class ParserException(content: String) : Exception(content)

‎src/test/kotlin/parser/JSONParserKtTest.kt

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package parser
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import net.quickwrite.parser.jsonParse
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import org.junit.jupiter.api.Test
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import org.junit.jupiter.api.Assertions.*
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import java.math.BigDecimal
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class JSONParserKtTest {
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@Test
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fun `null literal test`() {
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val input = "null"
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assertEquals(null, jsonParse(input))
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}
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@Test
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fun `true literal test`() {
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val input = "true"
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assertEquals(true, jsonParse(input))
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}
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@Test
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fun `false literal test`() {
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val input = "false"
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assertEquals(false, jsonParse(input))
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}
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@Test
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fun `number test`() {
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val inputs = arrayOf("1", "42", "42e2", "0.5", "1.42e2")
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inputs.forEach {
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assertEquals(BigDecimal(it), jsonParse(it))
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}
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}
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@Test
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fun `object test`() {
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val input = """
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{
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"hello": "World",
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"foo": "bar",
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"number": 42
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}
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""".trimIndent()
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val result = HashMap<String, Any?>()
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result["hello"] = "World"
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result["foo"] = "bar"
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result["number"] = 42
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assertEquals(result.toString(), jsonParse(input).toString()) // toString as the equals method is not completely implemented
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}
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@Test
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fun `array test`() {
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val input = """
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[1, 2, 3, "foo", "bar", null]
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""".trimIndent()
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val result = ArrayList<Any?>()
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result.add(1)
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result.add(2)
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result.add(3)
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result.add("foo")
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result.add("bar")
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result.add(null)
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assertEquals(result.toString(), jsonParse(input).toString())
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}
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@Test
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fun `nested test`() {
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val input = """
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{
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"test": [1, {
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"yay": []
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}
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]
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}
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""".trimIndent()
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val result = HashMap<String, Any?>();
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val array = ArrayList<Any?>()
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array.add(1)
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val map = HashMap<String, Any?>()
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map["yay"] = ArrayList<Any?>()
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array.add(map)
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result["test"] = array
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assertEquals(result.toString(), jsonParse(input).toString())
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}
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}

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