Examples for #THRIFT-1871

scenario1

// === Scenario 1: Today's Thrift, no null-safety ===

// IDL file
User {
  1: i32 id;
  2: optional i32 born;
  3: string name;
}
UserService {
  User getUserById(1: i32 id);
}

// Generated java code (pseudo)
class User {
  ...
  int getId() { ... }
  int getBorn() { ... }
  String getName() { ... }
}
class UserService {
  User getUserById(int id) { ... }
}

// Code usage - will have runtime errors
User user = userService.getUser(123); // Assume that user #123 exists
System.out.println(2013 - user.getBorn()); // If user#123 has no birth date specified, this will output 2013

User user2 = userService.getUser(456); // Now, assume that user #456 doesn't exist
System.out.println(user2.getName()); // NullPointerException!

scenario2

// === Scenario 2: How Scrooge (the alternative Thrift compiler) would compile the same IDL, and the resulting code ===

// IDL file
User {
  1: i32 id;
  2: optional i32 born;
  3: string name;
}
UserService {
  User getUserById(1: i32 id);
}

// Generated java code (pseudo)
class User {
  ...
  int getId() { ... }
  Option<Integer> getBorn() { ... }
  String getName() { ... }
}
class UserService {
  User getUserById(int id) { ... }
}

// Code usage - this error will be caught on compile-time
User user = userService.getUser(123); // Assume that user #123 exists
System.out.println(2013 - user.getBorn()); // We get a compile-time error here!

// This compiles, and works, no bugs:
if (user.getBorn().isDefined) {
  System.out.println(2013 - user.getBorn());
} else {
  System.out.println("Age unknown.");
}

// This error will still not be caught
User user2 = userService.getUser(456); // Now, assume that user #456 doesn't exist
System.out.println(user2.getName()); // NullPointerException!

scenario3

// === Scenario 3: Like scenario 2, but now a function's return value is allowed to be optional ===

// IDL file
User {
  1: i32 id;
  2: optional i32 born;
  3: string name;
}
UserService {
  optional User getUserById(1: i32 id);
}

// Generated java code (pseudo)
class User {
  ...
  int getId() { ... }
  Option<Integer> getBorn() { ... }
  String getName() { ... }
}
class UserService {
  Option<User> getUserById(int id) { ... }
}

// This error will be caught on compile-time!
User user2 = userService.getUser(456);
System.out.println(user2.getName()); // Compile-time error: Option<User> has no method "getName"

// This compiles, and works, no bugs:
if (user2.isDefined) {
  System.out.println(user2.getName());
} else {
  System.out.println("User not found");
}