TweetFollow Us on Twitter

Using Objects Safely In Object Pascal

Using Objects Safely In Object Pascal

CURT BIANCHI

In Object Pascal, objects are just like handles in that they refer to relocatable blocks of memory. To use objects safely, the programmer needs to recognize that the Macintosh Memory Manager can move the block of memory referred to by an object or handle, although only at well-defined times. This article gives guidelines for the safe use of objects in ObjectPascal.

The simplicity and elegance of Object Pascal's syntax is a two-edged sword. On the one hand, it makes Object Pascal feel like a natural extension to Pascal; on the other, it can lull a programmer into a false sense of security. For although the syntax of Object Pascal treats objects as though they were statically allocated, the fact is that in Object Pascal, objects arealways allocated as relocatable blocks (handles, in the vernacular) in the application heap. Thus, when you write Object Pascal programs for the Macintosh, you must be eternally aware that objects are handles, and program accordingly. This article tells you how to do that with MPW Pascal and TML Pascal, two compilers that can be used with MacApp in the MPW environment. In addition, it gives some tips for using handles outside the context of objects.

HOW OBJECT PASCAL IMPLEMENTS OBJECTS: A CAUTIONARY TALE

To get an idea of how Object Pascal implements objects, let's compare the code fragments in Figure 1. Each column of code accomplishes the same thing: the definition and use of a data structure representing a graphical shape. The only difference is that the left column is implemented with objects, while the right column is implemented with handles. The code in these two columns is very similar, and a comparison of the two reveals what goes on behind the scenes.
 1 TYPE
 2 TShape = OBJECT (TObject)
 3     fBounds: Rect;
 4     fColor: RGBColor;
 5     END;
 6
 7
 8
 9 VAR
10     aShape: TShape;
11     sameShape, copiedShape: TShape;
12
13 BEGIN
14 NEW(aShape);
15 FailNIL(aShape);
16
17 aShape.fBounds := gZeroRect;
18 aShape.fColor := gRGBBlack;
19
20 sameShape := aShape;
21
22 copiedShape := TShape(aShape.Clone);
23
24 FailNIL(copiedShape);
25
26 END;

 1 TYPE
 2 TShapeHdl = ^TShapePtr;
 3 TShapePtr = ^TShape;
 4 TShape = RECORD
 5     fBounds: Rect;
 6     fColor: RGBColor;
 7 END;
 8
 9 VAR
10     aShape: TShapeHdl;
11     sameShape, copiedShape: TShapeHdl;
12
13 BEGIN
14 aShape := TShapeHdl(NewHandle(SIZEOF(TShape)));
15 FailNIL(aShape);
16
17 aShape^^.fBounds := gZeroRect;
18 aShape^^.fColor := gRGBBlack;
19
20 sameShape := aShape;
21
22 copiedShape := aShape;
23 FailOSErr(HandToHand(Handle(copiedShape)));
24 FailNIL(copiedShape);
25
26 END;

Figure 1.
A Comparison of Code Implemented with Objects vs. Handles

The first thing to observe is that any variable of an object type is actually areference to an object. That is, the variable is a handle that refers to a block of memory containing the object's data. Thus, in the left column the value of the variableaShape is a handle. It contains the address of a master pointer that in turn points to the object's data. The size of the variableaShape is four bytes--the size of an address and not the size of the object itself. This is very much the same as the right column, in which the variableaShape is explicitly declared to be a handle. In fact, the only difference between the two is that the object version ofTShape has an implicit field containing the object's class ID, located just before the first declared field. The class ID is an integer value that allows the object's type to be identified at run time.

Line 14 of each column shows how a TShape data structure is created. Since handles must be dynamically allocated in the heap, it follows that objects must be dynamically allocated as well. This is the purpose of the call to NEW in the left column. Note that NEW works completely differently for objects and for other kinds of memory allocation. For objects, NEW generates a call to the internal library procedure %_OBNEW, which, aside from some debugging details, simply calls NewHandle, just like the handle-based code on the right does.

The call to FailNIL in line 15 detects the case where allocation of the object or handle fails. FailNIL is part of MacApp's failure-handling library and will be discussed in greater detail later.

Lines 17 and 18 reference fields of aShape. In the object code, the syntax leads you to believe that no handle dereferencing takes place, but of course we know better. What the Pascal compiler does is to implicitly dereference the handle for you. In other words, it does the very same thing as the code in the right column does explicitly.

Line 20 assigns one object reference to another, causing both aShape and sameShape to refer to thesame object. Line 22 (plus 23 in the right column) produces another shape whose contents are exactly the same as aShape. In the object case, the Clone method is used to produce a copy of the object referenced by aShape; copiedShape is assigned a reference to the newly created object. Clone is implemented by calling the Toolbox routine HandToHand, as is used in the right column. (FailOSErr is a MacApp routine that checks the result of HandToHand.) Since copying an object (or a handle) requires a memory allocation for the new object, FailNIL is used to ensure that the copy succeeded. The moral of this story is that you have to be very careful about how you use objects. For example, you must remember that every time you refer to a field of an object, you're really dereferencing a handle. If you're not careful, you're likely to wind up with a corrupt heap.

A PRIMER ON HANDLES AND THEIR PITFALLS

Handles have some interesting properties. If you've done any serious programming on the Macintosh (and I don't mean HyperTalk), then you know what I mean. If not, then (1) you've been spared the sorrows of a corrupt heap, and (2) you ought to get How to Write Macintosh Software , 2nd ed., by Scott Knaster (Hayden Books, 1988). Chapters 2 and 3 tell you all you need to know about handles. In the meantime, I'll give you a thumbnail description. In the heap, relocatable blocks of memory are referenced by double indirection, as shown in Figure 2. The first pointer (called the handle) points to a nonrelocatable pointer (called the master pointer), which in turn points to a block of memory. The Memory Manager can move the block of memory, and when this happens the address in the master pointer is changed to the block's new address.

[IMAGE _129-139_Using_Objects_h1.GIF]

Figure 2. A Handle to a Relocatable Block

This doesn't create a problem as long as you access the block via the handle. However, at times it's necessary or desirable for the sake of efficiency to dereference the handle--that is, make a copy of the block's master pointer, and then use that pointer to access the block by single indirection. And even this isn't a problem--as long as the block of memory doesn't move.

Well, we have bad news: it's bound to move at some point, when the Memory Manager needs to compact the heap. When this happens, the master pointer itself is correctly updated, but your copy of it is left dangling. Now for the good news: relocatable blocks of memory only move at certain well-defined times. Thus, the key to dereferencing handles is knowing when the blocks of memory they point to may move.

Oh, and one more bit of bad news: the Memory Manager has no garbage collection. This means you're responsible for disposing of handles when you've finished with them, and making sure you don't leave any dangling pointers.

PRACTICING SAFE OBJECT USAGE

Because the Memory Manager moves blocks of memory only at certain well-defined times, it's possible to come up with reliable guidelines for safe object usage. Keep these guidelines firmly in mind anytime you program in Object Pascal:1. Don't pass fields of objects as parameters to any routine unless you know it's safe.

In Pascal, when a routine is called, each parameter is passed by value or by address. Passing a parameter by value pushes a copy of the parameter's value onto the stack. Passing a parameter by address pushes the parameter's address onto the stack. (This should immediately trigger a handle alert in your head.) Passing thevalue of an object field is no problem. But passing theaddress of an object field on the stack is a potentially unsafe situation. That's because the address points to a memory location within an object--in other words, the object is dereferenced. If the object should happen to get relocated, the address won't point into the object anymore.

Because there's no way to predict what the address points to after memory relocation, and hence no way to predict the effect of using the address, all manner of strange things can occur. Making this type of bug extra difficult to track down is the fact that passing parameters unsafely works most of the time--it only fails when the heap is so full that the Memory Manager must relocate memory to satisfy a request. You do not want these kinds of bugs in your program.

Fortunately, Object Pascal programmers have a big advantage over their conventional colleagues: the compiler actually tells you when a field of an object is used in a potentially unsafe way. This occurs for VAR parameters, which by definition are passed by address, and for non- VAR parameters whose size is greater than four bytes. The latter case is because the compiler actually passes such parameters by address, expecting the called routine to use the address to make a local copy of the data.

If you stop to think about it, this error message is a really nice feature. Especially when compared to what the compiler does when any other handle is unsafely dereferenced, which is nothing. Nada. Zip. Even the most experienced and handle-cognizant of programmers occasionally writes code that unsafely dereferences a handle.

Let's look at an example. Consider the following definitions:

TYPE
    TShape = OBJECT (TObject)
    fBounds: Rect;
    fColor: RGBColor;
    END;

VAR aShape: TShape;

Attempting to compile the line

OffsetRect(aShape.fBounds, 10, 20);

results in the following error:

# OffsetRect(aShape.fBounds, 10, 20);
# ? 
### pascal - Error 815 Unsafe use of an object field 
as a var or > 4 byte parameter

In other words, this line of code has dereferenced the object's handle at a time when the object may move while it is dereferenced. In this case, the address of the field fBounds is computed and passed to OffsetRect. If aShape were to move before OffsetRect used it, then the computed address wouldn't point at fBounds anymore. Bombs away! Maybe the message ought to read "Error 815 You are about to commit yourself to spending an indeterminant number of days working with Macsbug. Please reconsider."

A simple way of avoiding the error is to avoid using the field as a parameter. Instead, use a temporary variable:

VAR
    r: Rect;

r := aShape.fBounds;
OffsetRect(r, 10, 20);
aShape.fBounds := r;

While this construct is guaranteed to be safe, it could be rather onerous if you had to do this every time you wanted to use an object field as a parameter. Actually, it turns out that many cases can easily be identified as safe because the routine being called doesn't trigger memory relocation. But how do you know when it's safe? Mostly, you need to know what causes objects to move.

Memory relocation can be triggered if (a) the called routine is in a different segment from the caller, since loading a segment may trigger memory relocation; (b) the called routine calls a ROM routine that triggers relocation; or (c) the called routine calls another routine that fits the criteria of (a) or (b). In the case of OffsetRect, it's in ROM so it won't require a segment load, and it is a ROM routine that doesn't move memory. (I know that because it isn't listed in Appendix A of theInside Macintosh XRef .)

When you do know it's safe (as with OffsetRect), you can turn off the compiler's parameter checking, effectively telling the compiler to keep quiet because you know what you're doing. Do this by using the $H compiler directive:

 {$Push}{$H-}
OffsetRect(aShape.fBounds, 10, 20);
 {$Pop}

The first line turns off parameter checking. $Push saves the state of the compiler directives; $H- tells the compiler not to check parameters for unsafe usage. In the second line the object field is used as a parameter. Because $H- was issued, no compiler error is generated. The third line uses $Pop to restore the state of the directives at the time the last $Push was issued.

The trick, of course, is in knowing when to use $H and when to use a copy of the object field instead. Based on the three causes of memory relocation, it's possible to identify the conditions in which you should avoid passing the field of an object as a parameter.

  1. Don't pass a field of an object as a VAR parameter, or a field greater than four bytes in size, in these circumstances:
    1. When the called routine is listed in Appendix A of the Inside Macintosh XRef .

      Appendix A lists routines defined in Inside Macintosh , volumes I-V, that may trigger memory relocation. These include all system-defined routines, such as those in ROM and in packages. Any routine defined in Inside Macintosh , volumes I-V, that does not appear in Appendix A will not trigger memory relocation. (A similar appendix appears in each Inside Macintosh book, but only applies to that book. So use the appendix in the XRef because it applies to all five volumes.)

    2. When the called routine is in a different, nonresident segment from the code generating the call.

      Calling a routine in another segment may require loading it into memory, potentially triggering memory relocation. If the called routine is in the same segment as the caller, then the segment must already be in memory and you're safe. If the called routine is in a different segment from the caller, you're still safe if the called routine's segment is a resident.

      Resident segments are defined by MacApp ® to be segments that are loaded into memory when the program starts up, and that stay in memory throughout the life of the program. Thus calling a routine in a resident segment never requires loading it into memory. If you know a routine is in a resident segment, you can call it without worrying about a segment load relocating memory. If you're not sure a routine is in a resident segment, play it safe.

    3. When the called routine is in the same segment as the caller, but the called routine indirectly causes segment loads by calling routines in other, nonresident segments. If you don't know whether a routine does this, then play it safe.
    4. When the called routine calls ROM routines that may trigger memory relocation. Again, if you're not sure, play it safe.

  2. Don't pass a field of an object or handle as the parameter to NEW.

    The parameter toNEW is aVAR parameter, and sinceNEW callsNewHandle, it most definitely may trigger memory relocation. Unfortunately, MPW Pascal compilers before version 3.1 didn't generate an error forNEW when you passed an object field as the parameter, and TML Pascal version 3.0 still doesn't. So be careful.

    Note that MacApp contains functions that allocate objects as well. The Clone method copies an object, returning a reference to the copy as its result. NewObjectByClassName and NewObjectByClassId create new objects. Because of the way the compiler generates code for functions, it is safe to assign a function result to the field of an object.

  3. Call FailNIL after every attempt to create an object, copy an object, or create a handle or pointer.

    FailNIL, defined in MacApp's UFailure unit, has a single parameter--a reference to an object, handle, or pointer. If that reference is NIL then FailNIL signals failure, essentially causing the application to back out of what it was doing and resume processing events. Calling FailNIL is how you verify that a memory allocation request actually succeeded. It works because the Memory Manager returns NIL if there isn't enough memory to satisfy a memory allocation. Since heaps have a finite amount of space, the potential exists that any allocation request can fail. So check each and every request just to make sure. Failure to heed this advice leads to bus errors and address errors when your program tries to dereference NIL handles.

    Be aware that this description of FailNIL just scratches the surface of MacApp's failure-handling facilities. The MacApp technical manuals go into greater detail than space permits in this article.

  4. Remember to free objects when you've finished with them, but only when you've finished with them!

    The Macintosh doesn't have automatic garbage collection, so you're responsible for freeing (disposing of) any objects you create. Failing to free objects when you've finished with them leads to a heap that slowly fills up with garbage, eventually suffocating the application.

    Keep in mind that when you free an object, any references to it are no longer valid and should be set to NIL. Nasty things happen if you use references to objects that no longer exist. If you're lucky, the MacApp debugger will stop your program the first time you refer to a nonexistent object. But sometimes even the MacApp debugger gets fooled. This happens if the memory occupied by the freed object hasn't yet been written over, or even worse, if another object or handle was allocated using the same master pointer as the object that was freed. (Try debugging that sometime!)

  5. If necessary, ensure that an object doesn't move by locking it.

    Sometimes it really makes life easier to ensure that an object won't be moved no matter what happens. Objects, like handles, can be locked. In fact, MacApp provides a method for this purpose. It's calledLock and it's defined inTObject so it can be used on any object. Lock takes aBoolean value as its only parameter, which when true "locks" the object's location in memory, and when false makes the object relocatable again. Lock returns aBoolean result that indicates whether the object was locked whenLock was called. This is handy because you can lock an object, do what you need to do, thenrestore the object's lock state to what it was before :

    VAR
        wasLocked: BOOLEAN;
    
    BEGIN
        wasLocked := anObject.Lock(TRUE);
        {do what you need to do}
        wasLocked := anObject.Lock(wasLocked);
    END;

    If you're not using MacApp, you can lock an object by casting it to be a handle and using HLock and HUnlock, the Memory Manager routines for locking and unlocking handles:

    HLock(Handle(anObject));
    { Do what you need to do. }
    HUnlock(Handle(anObject));

    Keep in mind that it's unwise to lock objects (or handles) for long periods of time. Nonrelocatable objects cause heap fragmentation, which reduces the effectiveness of the heap. (For further details, see Richard Clark's article "The Secret Life of the Memory Manager" in this issue.)

PRACTICING SAFE HANDLE USAGE

Even in an object-based program, it's occasionally necessary to use handles instead of objects. While handle usage is subject to the same guidelines just described for objects, there are some additional wrinkles:
  1. Don't count on the compiler to tell you when a handle's field is used unsafely.

    Unlike for fields of objects, the compiler doesn't produce an error when passing a field of a handle by address. All of the same problems with using fields of objects apply to fields of handles, but since the compiler offers no help in detecting unsafe uses, it's completely up to you to ensure that you use fields of handles safely. Chalk one up for objects.

  2. Beware of WITH statements that dereference handles. For example:

    TYPE
        TShapeHdl = ^TShapePtr;
        TShapePtr = ^TShape;
        TShape = RECORD
            fBounds: Rect;
            fColor: RGBColor;
        END;
    
    VAR
        aShape: TShapeHdl;
    
    BEGIN
        aShape := NewHandle(SIZEOF(TShape));
        FailNIL(aShape);
    
        WITH aShape^^ DO
            BEGIN
            fBounds := gZeroRect;
            fColor := gRGBBlack;
            END;
    END;

    Not only does the WITH statement simplify the Pascal text, it also lets the compiler perform code optimizations. Specifically, it stores the address fromaShape^^ in a register so that it can be reused throughout the scope of the WITH without being recomputed. As you might imagine, any operation that triggers memory relocation within the scope of the WITH will invalidate the address contained in the register. Bad news.

    By the way, using WITH statements on objects is okay! The compiler recognizes that the WITH is dereferencing an object and makes sure safe code is generated. Objects 2, handles 0.

  3. Don't assign a function result to a field of a handle unless you know the calling function won't trigger memory relocation.

    For example, using the shape definitions given above, this is a potentially unsafe use of a handle field:

    aShape^^.fBounds := FunctionThatReturnsARect;

    The problem is that the Pascal compiler dereferences the handle aShape before calling the function. Thus, a function that triggers memory relocation or is in another segment will invalidate the address obtained by dereferencing the handle.

    Once again, this type of usage is okay for objects. As for WITH statements, the compiler recognizes when a function result is assigned to an object field and ensures that safe code is generated.

IN CONCLUSION

In conclusion, you can avoid the pitfalls in writing Object Pascal programs, by understanding how objects work and by using the guidelines described in this article. Then instead of having to spend undue time debugging, you can relax and enjoy the advantages of object-based programming.

CURT BIANCHI, displaced Lakers fan, has never met a taco he didn't like. He's been at Apple more than three years, where he first worked on MacApp and now concentrates on future system software. This southern California native (he asks you not to hold that against him) earned a BSICS in 1981 from the University of California-Irvine, followed by stints at Link Systems and Monogram Software, and self-employment doing software odd jobs, including working on computer dating software. His hobbies include music, photographing trains, avoiding serious injury on the basketball court, and rooting for the Lakers from afar .*

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

jAlbum 19.2 - Create custom photo galler...
With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly, with pro results - Simply drag and drop photos into groups, choose a design... Read more
BlueStacks 4.140.13 - Run Android applic...
BlueStacks App Player lets you run your Android apps fast and fullscreen on your Mac. Feature comparison chart Version 4.140.13: Highlights/Bug Fixes: Feel free to use BlueStacks as your go to... Read more
Adobe Premiere Pro CC 2020 14.0.1 - Digi...
Premiere Pro CC 2020 is available as part of Adobe Creative Cloud for as little as $52.99/month. The price on display is a price for annual by-monthly plan for Adobe Premiere Pro only Adobe Premiere... Read more
VirtualBox 6.1.2 - x86 virtualization so...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
RoboForm 8.6.8 - Password manager; syncs...
RoboForm is a password manager that offers one-click login, mobile syncing, easy form filling, and reliable security. Password Manager. RoboForm remembers your passwords so you don't have to! Just... Read more
Postbox 7.0.11 - Powerful and flexible e...
Postbox is a new email application that helps you organize your work life and get stuff done. It has all the elegance and simplicity of Apple Mail, but with more power and flexibility to manage even... Read more
calibre 4.9.0 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Notability 4.2 - Note-taking and annotat...
Notability is a powerful note-taker to annotate documents, sketch ideas, record lectures, take notes and more. It combines, typing, handwriting, audio recording, and photos so you can create notes... Read more
FoldersSynchronizer 5.0.1 - Synchronize...
FoldersSynchronizer is a popular and useful utility that synchronizes and backs-up files, folders, disks and boot disks. On each session you can apply special options like Timers, Multiple Folders,... Read more
Sketch 62 - Design app for UX/UI for iOS...
Sketch is an innovative and fresh look at vector drawing. Its intentionally minimalist design is based upon a drawing space of unlimited size and layers, free of palettes, panels, menus, windows, and... Read more

Latest Forum Discussions

See All

The Alliance update to Out There: Omega...
Out There is an old go-to recommendation for a lot of mobile stalwarts, but I could never really get into it. This sci-fi survival game that blended elements of interactive fiction and roguelike mechanics just felt a little off-balance and a little... | Read more »
Animal Fury Destination is an action-adv...
Animal Fury Destination is an action-adventure game from independent, Colombian developer Ignicion Games. It's a 3D action game where you'll play as various different characters as you embark on a quest to stop an evil crow sorcerer. [Read more] | Read more »
Shadowgun War Games Closed Beta Impressi...
Shadowgun: War Games is an upcoming free-to-play multiplayer shooter that’s essentially just an Overwatch knock-off. There are hero characters with special abilities, and you compete in 5-v-5 game modes where the goal is to use superior team... | Read more »
Slingsters is a physics-based puzzler fo...
Slingsters is a physics-based puzzle game where the aim is to collect various different monsters by flinging them from one side of a level to the other and into a box. It's also the first game from Nappy Cat and is available now for iOS and... | Read more »
Spiritwish's latest update sees the...
A sizeable update has hit Nexon's MMORPG Spiritwish today. It brings a new game mode, characters and there will also be a special event to celebrate the update with a firework display. [Read more] | Read more »
Maze Machina, a turn-based puzzler from...
The latest game from Arnold Rauers also known as Tiny Touch Tales is now available. You may be familiar with one of his many excellent titles such as Card Crawl, Enyo and Card Thief. His latest endeavour is called Maze Machina and you can grab it... | Read more »
Mario Kart Tour's Ice Tour races to...
Can you believe Mario Kart Tour is already on its 9th tour? The game only launched back in September, and since then it's become increasingly tricky to keep on top of the amount of new content Nintendo is pumping out. [Read more] | Read more »
Apple Arcade: Ranked - Top 50 [Updated 1...
In case you missed it, I am on a quest to rank every Apple Arcade game there is. [Read more] | Read more »
Marvel Future Fight's latest update...
Marvel Future Fight's latest update has added an all-new team of heroes to recruit and do battle with. The 'Warriors of the Sky' include Blue Dragon, War Tiger, Sun Bird, and Shadow Shell. As is the norm, each character comes with their own unique... | Read more »
Klee: Spacetime Cleaners is a fast-paced...
Klee: Spacetime Cleaners is a fast-paced auto-shooter that sports a cute retro aesthetic thathad racked up an impressive 100,000 pre-registers prior to its release. It's available now for both iOS and Android. [Read more] | Read more »

Price Scanner via MacPrices.net

Just in! Apple iMacs on sale for $100-$150 of...
B&H Photo has new 2019 21″ and 27″ 5K iMacs on stock today and on sale for up to $150 off Apple’s MSRP, with prices starting at only $999. These are the same iMacs sold by Apple in their retail... Read more
Save $100 on the 13″ 1.4GHz MacBook Pro at th...
Apple resellers have 13″ 1.4GHz MacBook Pros on sale today for $100 off Apple’s MSRP, and some are including free overnight delivery: (1) Amazon has new 2019 13″ 1.4GHz MacBook Pros on sale for $100... Read more
AT&T offers free 64GB Apple iPhone XS wit...
Open a new line of service with AT&T, and they will include a free 64GB iPhone XS. Credit for the phone is applied monthly over a 30 month lease. The fine print: “Limited Time Requires new line... Read more
New Verizon deal: Apple iPhone XR for $300 of...
Switch to Verizon and sign up with one of their Unlimited plans, and Verizon will take $300 off the price of an Apple iPhone XR (regularly $749), plus get a free $200 prepaid Mastercard. This is an... Read more
Amazon’s popular AirPods sale is back with mo...
Amazon has new 2019 Apple AirPods on sale today ranging up to $40 off MSRP, starting at $129, as part of their popular Apple AirPods sale. Shipping is free: – AirPods Pro: $234.98 $15 off MSRP –... Read more
Apple’s top of the line 10.5″ 256GB WiFi + Ce...
B&H Photo has the top of the line 10.5″ 256GB WiFi + Cellular iPad Air on sale for $599 shipped. That’s $180 off Apple’s MSRP for this model and the cheapest price available. Overnight shipping... Read more
Apple’s refurbished iPad Pros are the cheapes...
Apple has Certified Refurbished 11″ iPad Pros available on their online store for up to $220 off the cost of new models. Prices start at $679. Each iPad comes with a standard Apple one-year warranty... Read more
Just in: Take $100 off the price of the 3.0GH...
Apple resellers are offering new 2018 6-Core Mac minis for $100 off Apple’s MSRP today, only $999. B&H Photo has 6-Core Mac minis on sale for $100 off Apple’s standard MSRP. Overnight shipping is... Read more
Apple has 4-core and 6-core 2018 Mac minis av...
Apple has Certified Refurbished 2018 Mac minis available on their online store for $120-$170 off the cost of new models. Each mini comes with a new outer case plus a standard Apple one-year warranty... Read more
Amazon offers $200 discount on 13″ MacBook Ai...
Amazon has new 2019 13″ MacBook Airs with 256GB SSDs on sale for $200 off Apple’s MSRP, now only $1099, each including free shipping. Be sure to select Amazon as the seller during checkout, rather... Read more

Jobs Board

*Apple* Mobility Pro - Best Buy (United Stat...
**744429BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000574-Garner-Store **Job Description:** At Best Read more
Geek Squad *Apple* Consultation Professiona...
**757963BR** **Job Title:** Geek Squad Apple Consultation Professional **Job Category:** Store Associates **Store NUmber or Department:** 000433-Henrietta-Store Read more
*Apple* Computing Professional - Best Buy (U...
**754611BR** **Job Title:** Apple Computing Professional **Job Category:** Store Associates **Store NUmber or Department:** 000142-Milpitas-Store **Job Read more
Best Buy *Apple* Computing Master - Best Bu...
**745058BR** **Job Title:** Best Buy Apple Computing Master **Job Category:** Store Associates **Store NUmber or Department:** 001080-Lake Charles-Store **Job Read more
Geek Squad *Apple* Consultation Professiona...
**756640BR** **Job Title:** Geek Squad Apple Consultation Professional **Job Category:** Store Associates **Store NUmber or Department:** 000484-Manchester-Store Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.