conversations.from: human
conversations.value: What could be a title for a book about Technologist, Web with the genre: Computers & Technology, Programming?
conversations.from: assistant
conversations.value: A title for this book could be 'Pro Objective-C'
conversations.from: human
conversations.value: Give me the first paragraph for this book.
conversations.from: assistant
conversations.value: Pro Objective-C
  The NSHost class contains methods to access information for a network host, which is a collection of network names and addresses for a computer or device connected to a network. An NSHost object represents an individual network host. Its methods can be used to look up the network name and address information for the host or other objects on a network. The code in Listing 11-1 uses the NSHost currentHost and name methods to retrieve the NSHost object for the host the program is running on, and then logs the host name to the console.
conversations.from: human
conversations.value: Give me five more paragraphs.. Start with the sentence 'NSMutableDictionary supports both getting and setting the elements of an array using the subscript operand'.
conversations.from: assistant
conversations.value: NSMutableDictionary supports both getting and setting the elements of an array using the subscript operand. Listing 16-15 creates a mutable dictionary from an NSDictionary literal, and then sets an element of the array to a new value.
  The NSDictionary and NSMutableDictionary classes use the subscript operand (i.e., a key) to access the appropriate element from its collection. The subscripting operator does not allow you to add elements to a mutable array; it only allows you to replace existing elements. For NSDictionary or NSMutableDictionary instances, attempting to retrieve an element via subscripting returns nil if there is no value associated with the input key. When setting an NSMutableDictionary element using subscripting, the method raises an NSInvalidArgument exception if the key or object is nil.
  When the subscript operand is applied on an NSDictionary or NSMutableDictionary object, the expression is rewritten to use one of two different selectors, depending on whether the element is being read or written. For read (i.e., get) operations, the compiler translates this into an expression using the NSDictionary method objectForKeyedSubscript:. In effect, the following two expressions are equivalent:
  For write (i.e., set) operations, the compiler translates this into an expression that uses the NSMutableDictionary method setObject:forKeyedSubscript:. In effect, the following two expressions are equivalent:
  The NSDictionary method objectForKeyedSubscript: takes an Objective-C pointer type that conforms to the NSCopying protocol as its input parameter and returns a value of some Objective-C object pointer type. The NSMutableDictionary method setObject:forKeyedSubscript: takes an Objective-C pointer type as its first parameter and an Objective-C pointer type that conforms to the NSCopying protocol as its second parameter.
conversations.from: human
conversations.value: Give me the last five paragraphs.
conversations.from: assistant
conversations.value: The return value of 25 (shown in Figure C-13) is correct. Next, select continue in the debug bar (you may have to click the button two or three times). The output console logs Sum 1 = 25, per the breakpoint action debugger command that you configured earlier. Now observe that the debugger has paused again at the line breakpoint set for the sumAddend1:addend2: method. This time, use the debugger po command in the debug area content pane to display the values for the two parameters:
  These values (10, –25) are as expected, so select continue to advance the program. Next, the debugger pauses at the NSCAssert. Using the po command, the variable sum2 displays a value of –15 (as shown in Figure C-15).
  This is the expected value, so why is the assertion failing? Looking at the assertion statement, you can see that the conditional expression is expecting a value of 15, when it should be –15!
  When you correct the assertion (by changing the value to –15) and run the program again, you will see that it runs successfully. Now even though this was a very contrived example, it illustrates a few of the capabilities of debugging in Xcode using LLDB. Apple provides a variety of documentation on Xcode debugging using LLDB, and the LLDB web site is an essential reference for more information.
  In this appendix, you learned about debugging using LLDB, the default debugger for Xcode. Debugging is a mandatory part of software development, so it's vital to master this skill to become a more efficient, productive programmer. By now I hope that you are convinced of the power and capability of LLDB, and that you will take the time to become skilled at using it on all of your Objective-C software development projects.