我正在使用swift enum。我的enum看起来像这样：
enum DataStructures<T> {
case element(value: T)
case elements(value: [T])
}
我像这样初始化DataStructures：
DataStructures.element(value: resultElement)
resultElement属于ResultElement类型：
resultElement: ResultElement
我的问题是：有没有办法从枚举resultElement中提取case的值，以便在DataStructures.element(value: resultElement)通过后恢复该对象以某种方法作为参数？该参数也是这样的：
data: DataStructures<ResultElement>
感谢您的回答。
答案 0 :(得分：1)
使用模式匹配：
fetchedResultsController答案 1 :(得分：1)
import java.io.IOException;
import java.io.LineNumberReader;
import java.io.PrintWriter;
import java.io.Reader;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class ScriptRunner {
private static final String DEFAULT_DELIMITER = ";";
private static final String DELIMITER_LINE_REGEX = "(?i)DELIMITER.+";
private static final String DELIMITER_LINE_SPLIT_REGEX = "(?i)DELIMITER";
private final Connection connection;
private final boolean stopOnError;
private final boolean autoCommit;
private PrintWriter logWriter = new PrintWriter(System.out);
private PrintWriter errorLogWriter = new PrintWriter(System.err);
private String delimiter = DEFAULT_DELIMITER;
private boolean fullLineDelimiter = false;
/**
* Default constructor.
*
* @param connection
* @param autoCommit
* @param stopOnError
*/
public ScriptRunner(Connection connection, boolean autoCommit, boolean stopOnError) {
this.connection = connection;
this.autoCommit = autoCommit;
this.stopOnError = stopOnError;
}
/**
* @param delimiter
* @param fullLineDelimiter
*/
public void setDelimiter(String delimiter, boolean fullLineDelimiter) {
this.delimiter = delimiter;
this.fullLineDelimiter = fullLineDelimiter;
}
/**
* Setter for logWriter property.
*
* @param logWriter
* - the new value of the logWriter property
*/
public void setLogWriter(PrintWriter logWriter) {
this.logWriter = logWriter;
}
/**
* Setter for errorLogWriter property.
*
* @param errorLogWriter
* - the new value of the errorLogWriter property
*/
public void setErrorLogWriter(PrintWriter errorLogWriter) {
this.errorLogWriter = errorLogWriter;
}
/**
* Runs an SQL script (read in using the Reader parameter).
*
* @param reader
* - the source of the script
* @throws SQLException
* if any SQL errors occur
* @throws IOException
* if there is an error reading from the Reader
*/
public void runScript(Reader reader) throws IOException, SQLException {
try {
boolean originalAutoCommit = connection.getAutoCommit();
try {
if (originalAutoCommit != autoCommit) {
connection.setAutoCommit(autoCommit);
}
runScript(connection, reader);
} finally {
connection.setAutoCommit(originalAutoCommit);
}
} catch (IOException e) {
throw e;
} catch (SQLException e) {
throw e;
} catch (Exception e) {
throw new RuntimeException("Error running script. Cause: " + e, e);
}
}
/**
* Runs an SQL script (read in using the Reader parameter) using the connection passed in.
*
* @param conn
* - the connection to use for the script
* @param reader
* - the source of the script
* @throws SQLException
* if any SQL errors occur
* @throws IOException
* if there is an error reading from the Reader
*/
private void runScript(Connection conn, Reader reader) throws IOException, SQLException {
StringBuffer command = null;
try {
LineNumberReader lineReader = new LineNumberReader(reader);
String line = null;
while ((line = lineReader.readLine()) != null) {
if (command == null) {
command = new StringBuffer();
}
String trimmedLine = line.trim();
if (trimmedLine.startsWith("--")) {
println(trimmedLine);
} else if (trimmedLine.length() < 1 || trimmedLine.startsWith("//")) {
// Do nothing
} else if (trimmedLine.length() < 1 || trimmedLine.startsWith("--")) {
// Do nothing
} else if (!fullLineDelimiter && trimmedLine.endsWith(getDelimiter())
|| fullLineDelimiter && trimmedLine.equals(getDelimiter())) {
Pattern pattern = Pattern.compile(DELIMITER_LINE_REGEX);
Matcher matcher = pattern.matcher(trimmedLine);
if (matcher.matches()) {
setDelimiter(trimmedLine.split(DELIMITER_LINE_SPLIT_REGEX)[1].trim(),
fullLineDelimiter);
line = lineReader.readLine();
if (line == null) {
break;
}
trimmedLine = line.trim();
}
command.append(line.substring(0, line.lastIndexOf(getDelimiter())));
command.append(" ");
Statement statement = conn.createStatement();
println(command);
boolean hasResults = false;
if (stopOnError) {
hasResults = statement.execute(command.toString());
} else {
try {
statement.execute(command.toString());
} catch (SQLException e) {
e.fillInStackTrace();
printlnError("Error executing: " + command);
printlnError(e);
}
}
if (autoCommit && !conn.getAutoCommit()) {
conn.commit();
}
ResultSet rs = statement.getResultSet();
if (hasResults && rs != null) {
ResultSetMetaData md = rs.getMetaData();
int cols = md.getColumnCount();
for (int i = 0; i < cols; i++) {
String name = md.getColumnLabel(i);
print(name + "\t");
}
println("");
while (rs.next()) {
for (int i = 1; i <= cols; i++) {
String value = rs.getString(i);
print(value + "\t");
}
println("");
}
}
command = null;
try {
if (rs != null) {
rs.close();
}
} catch (Exception e) {
e.printStackTrace();
}
try {
if (statement != null) {
statement.close();
}
} catch (Exception e) {
e.printStackTrace();
// Ignore to workaround a bug in Jakarta DBCP
}
} else {
Pattern pattern = Pattern.compile(DELIMITER_LINE_REGEX);
Matcher matcher = pattern.matcher(trimmedLine);
if (matcher.matches()) {
setDelimiter(trimmedLine.split(DELIMITER_LINE_SPLIT_REGEX)[1].trim(),
fullLineDelimiter);
line = lineReader.readLine();
if (line == null) {
break;
}
trimmedLine = line.trim();
}
command.append(line);
command.append(" ");
}
}
if (!autoCommit) {
conn.commit();
}
} catch (SQLException e) {
e.fillInStackTrace();
printlnError("Error executing: " + command);
printlnError(e);
throw e;
} catch (IOException e) {
e.fillInStackTrace();
printlnError("Error executing: " + command);
printlnError(e);
throw e;
} finally {
conn.rollback();
flush();
}
}
private String getDelimiter() {
return delimiter;
}
private void print(Object o) {
if (logWriter != null) {
logWriter.print(o);
}
}
private void println(Object o) {
if (logWriter != null) {
logWriter.println(o);
}
}
private void printlnError(Object o) {
if (errorLogWriter != null) {
errorLogWriter.println(o);
}
}
private void flush() {
if (logWriter != null) {
logWriter.flush();
}
if (errorLogWriter != null) {
errorLogWriter.flush();
}
}
}
可以在这里推荐你（参见Associated Values部分）： https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Enumerations.html
祝你好运！