Ha ha! You fool! You fell victim to one of the classic blunders, the most famous of which is “never get involved in a land war in Asia.” But only slightly less well-known is this: “Never have an auto-synthesized property and an instance variable with the same name when death is on the line!”—Vizzini
At work, my team decided to drop support for iOS 4. Most of our customers have upgraded to iOS 5.1. Surprisingly, very few are still using iOS 5.0. I guess over-the-air upgrades are working really well for people.
Our app is old. In some places we still checked if the user had upgraded to iOS 3 yet. :) My team spent the week on cleanup and paying down technical debt. My job was to:
- Convert to using object literals for arrays, dictionaries and numbers.
- Switch all of our instance variables to properties.
I love shortening and removing code without losing functionality. The first two tasks went fairly quickly. But I…uh…learned a lot while tackling number three.
You can declare an instance variable in an
@interfaceblock — either the public interface in the
.hfile or the private interface in the
.mfile. You can also declare one in the
@implementationblock in the
.mfile. Or all three at once.
You can mix instance variables, properties and auto-synthesized properties. But auto-synthesized properties are so much nicer: less code, less maintenance, less boilerplate typing. Here are 3 tips to help you use properties more effectively.
1. Deal With Read-Only Properties
An auto-synthesized property generates an instance variable with the same name as the property except prefixed with an underscore. This is great because it’s clear whether you’re using the property (
self.myprop) or the instance variable (
_myprop). Using the bare name (
myprop) doesn’t even compile, so you limit the confusion and bugs caused by accidental mistypes.
Auto-synthesized properties create their own getter and setter methods (avoiding some unnecessary typing). You can implement your own getter and/or setter, in which case those methods are not automatically generated. The instance variable (
_myprop) is still synthesized.
However, if your property is
readonlyAND you implement your own getter method, then an instance variable is not synthesized. I suspect this is to allow for a named property that is dynamically calculated. In any case, if you would like an instance variable, you can force it to be synthesized by either:
@synthesize myprop = _myprop;in your
- Redeclaring the property as
readwritein your private
The second option works like inheritance in that you can redeclare a property as less-restrictive but not the other way. Redeclaring a public
readwriteproperty as privately
readonlyisn’t possible, though why you’d want to do that remains a mystery.
2. Avoid Instance Variables
It is a Bad Thing™ to have both an auto-synthesized property and an instance variable declared with the same name.
self.myprop = 1uses the auto-synthesized instance variable
myprop = 1uses the declared instance variable
_myprop= 1 uses the auto-synthesized instance variable
Since you end up with two instance variables, when you probably intended to have only one, doing this can cause lots of unexpected bugs and problems. Better to avoid declaring instance variables for your synthesized properties.
It is a Worse Thing™ to have two auto-synthesized properties of the same name with one prefixed with an underscore.@property myprop; @property _myprop;
This causes problems because
self._mypropis different than
_mypropwhen you really should have used
__myprop, making you start to wonder about your own sanity. This doesn’t seem like it would happen much, but it can if you are importing several
.hfiles, one of which uses underscores in its property names.
So don’t do that. :)
3. Use Instance Variables Correctly
In most cases, it’s best to stick with using the property (
self.myprop) in your code. However, it’s important to use the instance variable (
_myprop) in two cases:
- In your
init:methods to avoid possible side-effects if you implement your own setter later, and
- In your custom getter and setter methods to avoid infinite recursion (always nice).
Auto-synthesized properties are great. Not quite as awesome as ARC, but close.
A delicious recipe for bacon candy from my friend Randy Hall:
- 1 pound thick-cut bacon
- 1 cup brown sugar
- 1 teaspoon cayenne (optional)
- 2 teaspoons favorite BBQ dry rub (optional)
Preheat the oven to 375 degrees. Mix brown sugar, cayenne, and BBQ rub together in a medium bowl. Place sugar mixture a gallon Ziploc bag. Add bacon and toss. Line a baking sheet with foil, and place a wire rack in the baking sheet. Lay the strips of bacon on the rack. Pat any remaining sugar mixture on the bacon. Put the baking sheet on the top rack of the oven and bake until crisp, about 20-25 minutes, turning once halfway through (re-coat with any additional sugar when turning if you want even more candy coating). When the bacon reaches desired crispiness, remove from the oven to a serving dish and let cool slightly before serving.
It’s a super simple recipe. The only real gotcha is finding the fine line between nice crispy bacon and black burnt sugary mess. Check it often at the end. It is delicious.
Buying a mattress is a terrible experience. A mattress is something we buy only rarely. So each time we head out shopping, we’re unfamiliar with the current trends in mattress technology, comfort and safety. Like many other manufacturers, mattress makers often try to save money by using low quality materials or construction methods, especially on the inside where it’s hard to see. A month ago, my wife and I bought a bigger bed and needed to replace our mattress. Here is what I discovered.
Mattresses are often made from materials that can be politely described only as unnatural. Over time, they can break down, wear out, give off potentially harmful gasses and quickly become uncomfortable. If you have allergies or are sensitive to smells, noises or motion transfer, buying the wrong mattress could lead to years of difficulty getting a good night’s rest.
I spent way too much time reading, searching and researching on the Internet. I ruled out foam because of off-gassing, odor and durability. Innerspring mattresses are bad at preventing motion transfer, even the ones with separately wrapped coils (which is what we’ve been sleeping on for the last few years). While there are many mattress that use a combination of materials, a solid latex mattress seems like the best option.
Latex is the tree sap from which rubber is made. A latex mattress is made from natural rubber foam molded into shape using one of two processes: dunlop or talalay. Dunlop is older, while Talalay produces a slightly finer and more even foam. Synthetic latex is also used in mattresses. A “blended” latex mattress is a mix of natural and synthetic latex. If you have a latex allergy, you’ll want a synthetic mattress. If not, natural latex seems to last longer.
Latex mattresses are most often composed of several layers of latex stacked on top of one other, encased in a cover. Latex layers (and toppers) are made by only a few large corporations. You can ask the manufacturer where they get their latex. Latex International seems to be highly regarded.
Latex layers have different levels of firmness measured in ILD (Indentation Load Deflection). Soft latex typically has an ILD of 20-25, while firm latex might be 35-40. The most common arrangement seems to be 3″ of firm latex on the bottom, 3″ of medium latex in the middle and 3″ of soft latex on the top. Another common option is 6″ of firm on the bottom with 2″ of medium or soft on top. Having several 3″ layers with differing firmness gives you the flexibility to rearrange them if desired. For example, moving the soft layer to the middle and putting the medium layer on top gives the mattress a firmer feel without requiring another purchase.
Most covers (also called ticking) for a latex mattress will have a zipper so you can swap layers or stack them in a different order. The best covers are made from quilted cotton with wool padding. The quilting keeps the padding from bunching up over time.
By law, mattress cover padding must be resistant to fire. Wool is naturally fire-resistant. Other materials, like polyester, must be chemically treated to provide resistance. If you’re going the latex route, especially for health or environmental reasons, it seems best to avoid chemically treated synthetic material in your mattress, all of which can off-gas.
Getting a mattress pad is important to protect the mattress from spills because latex and most mattress covers are not machine washable. Any pad labeled “waterproof” is going to have a layer of vinyl or plastic, or use a thin coating of polyethylene or polyurethane. Water-resistant pads are available in cotton, cotton-and-polyester and cotton-and-wool varieties. Pads range from 1/4″ to 1.5″ thick.
Latex and other foam mattresses do not require box springs. Instead, if extra height is needed, use a mattress foundation. A foundation is basically a wooden box covered by fabric that does not have springs. They vary from 4″ to 10″ in height. Most foundations have wooden slats on top. The gap between slats ranges from 2″ (very good) to 5″ (less so). Too much space between slats allows the mattress to sag and decreases back support and the lifetime of the mattress. The covers for many self-assembled foundations use a drawstring and are open on the bottom.
If you have a box spring that you’d like to continue using, you can put plywood (or something similar) on top to help improve support and stability.
Buying high-quality cotton sheets seems easy. The best sheets are woven from single-ply thread made from Supima™ or Egyptian cotton. Thread counts in the range 400-800 are great. Any higher and the sheets start to feel flimsy because of how thin the thread has to be.
Sadly, there have been many cases of manufacturers lying about thread counts or using fabric incorrectly labeled as Egyptian. And make sure your sheets say “100%” or else they may not be. A good return policy is your best defense.
Where To Buy Online
If you are shopping online, there are many places to buy a latex mattress. You can even buy latex layers and a cover separately as a money-saving DIY project. What’s The Best Mattress is a good place to do research. There is a great list of places to start shopping. I looked at PlushBeds, Rocky Mountain Mattress, SleepEZ, Foam By Mail, Foam Sweet Foam, Tranquility Mattress and The Natural Bed Store. Be sure to check the return policies because shipping costs, restocking fees, return periods and warranties all vary.
Interestingly, nearly all of the foundations I found online were re-branded versions of this one. Look for that image as you’re shopping. Alternatives include one by U.S. Box Spring and another by Bed In A Box, which is manufactured by KD Frames. Any foundation from a local store will work too. If you buy locally, you can probably have your old mattress taken away for free.
Here’s What I Did
I decided on a DIY project. I ordered a cotton-and-wool cover and three latex layers from mattresses247 on eBay: one soft, one medium, one firm. Their latex layers are blended “factory seconds” which are new, but have cosmetic defects — like lumpy M&Ms that can’t be sold at retail. The defects are visible, but do not seem to affect the feel of the mattress at all. And saving $1,000 is pretty nice. They have great return policy (30 days, no restocking fees, only pay return shipping). Valerie was responsive and very helpful over email.
I bought the American Hardwood Mattress Foundation from BedInABox. It’s extremely well made and perfectly quiet. The cover is open on the bottom and made from polyester and cotton, which was a little disappointing at first. Polyester doesn’t off-gas much, and I can buy another cover later if I want. The slats have a 3.5″ gap, which seems a little wide considering the price. I nailed using some thin sheets of hard material on top of the slats to try to avoid sagging. But while looking underneath later on, it didn’t seem like the mattress was sinking into the remaining gaps much.
UPDATE Oct 10, 2012: Scott Ravenhorst, owner of Foam Sweet Foam, reached out to me about my experience. I’ve updated my comments here to reflect that.
I ordered my first mattress pad from Foam Sweet Foam. I really liked the quality and construction, but ended up returning it. Foam Sweet Foam has a great return policy and gladly took it back despite the fact I had washed it twice. The owner later read my article and called me about my experience. He confirmed I’d gotten a defective pad and that nearly all of their customers are very happy. If I hadn’t already found an alternative, I would have given them another shot. Foam Sweet Foam takes good care of their customers, which isn’t something that is common on the Internet.
My second pad is a Washable Wool-Filled Fitted Mattress Pad by Natura World from Amazon. I confirmed with Natura that the “Wash N Snuggle” fitted pad is the same product as the “Washable Wool-Filled” fitted pad. We’ve been sleeping on it for
a week four months, and I really like it. We aired it out for a day, washed it once, and can’t smell anything.
I ordered two sets of sheets from Costco. They have a great reputation and return policy. While I liked the Charisma Egyptian cotton sheets, I ended up keeping the Kirkland Supima sheets. They are really soft, seem durable and feel great.
Overall, I’m very happy with my new mattress: latex, hardwood foundation, cotton-and-wool cover and pad, high-quality cotton sheets. It’s true that it takes a while to get used to a new mattress, and it’s only been a week. But I find myself looking forward to laying down at night. It’s too soon to say if I’m sleeping better, but I definitely find myself smiling more.
UPDATE 2012-04-24: My March estimate of 11.8 million was accurate. I’ve added a link below and updated the image to reflect the change.
UPDATE 2012-08-01: My July estimate of 23.3 million was way off. Like Asymco says, “It’s perhaps unrealistic to expect 150% growth for more than one year.”
Back in September, I estimated that Apple would sell 200 million iPads by the end of 2012. It looks like I was a little too optimistic.
Apple just reported stellar quarterly results. However, iPad sales growth was not quite as strong as Apple’s initial sales seemed to indicate. Two years after introduction, the iPad is selling better than the iPhone did two years after its debut. But it looks like it may take one extra quarter for Apple to hit 200 million iPads.
- Apr to Jun 2010: 3.27 million
- Jul to Sep 2010: 4.19 million
- Oct to Dec 2010: 7.33 million
- Jan to Mar 2011: 4.69 million
- Apr to Jun 2011: 9.25 million
- Jul to Sep 2011: 11.1 million
- Oct to Dec 2011: 15.4 million
- Jan to Mar 2012: 11.8 million (this was accurate)
- Apr to Jun 2012: 23.3 million (actual amount was 17.0 million)
- Jul to Sep 2012: 28.0 million
- Oct to Dec 2012: 38.9 million
- Jan to Mar 2013: 29.8 million (was 29.9 due to rounding differences)
Disclosure: I own AAPL stock.
One of the things Josh covered was what should happen during the first 100 days (14 weeks) of a high-tech startup.
Week 1 — Research and choose business
Week 2 — Build financial model and development plan
Week 3 — Build pitch with screenshots and practice
Week 4 — Interview law firm, staff and advisers
Week 5 — Incorporate and setup shop with office space and equipment
Week 6 — Initial documents, books, hires and cap table
Week 7 — Create website and logo (do a trademark search)
Week 8 — Identify 10 to 20 potential investors and study who else they invest in
Week 9 — Practice the pitch and setup meeting with the least important investor
Week 10 — Interview, build product, pitch again
Week 11 — Interview, build product, pitch again
Week 12 — Interview, build product, pitch again
Week 13 — Interview, build product, pitch again
Week 14 — Interview, build product, pitch again
He recommended interviewing one potential employee every day. Pitching to the least important investor first lets you have a chance to practice in a situation where making a mistake isn’t as damaging.
I first met Josh just after publication of an article he wrote on how many angel investors in Utah were doing it wrong. The article, entitled “Poison in the Well”, in addition to having a great title, was direct and clear in its criticism. It was one of the reasons I later applied to work at Mozy.
For anyone who knows him, I think “direct and clear criticism” is a good phrase to describe what it’s like to work for Josh. His class was no exception. It was a great chance to learn from someone who’s been there and done it successfully.
Seth Godin says there are four stages to every “game” that we play in life. These are projects and activities in which we are involved. We even use game-like labels for some of these: the dating game, the corporate ladder, the rat race. I’d never before thought of them directly as games that could be played.
- You don’t even realize there’s a game.
- You start getting involved and it feels like a matter of life or death.
- You realize that it’s a game and you play it with strategy.
- You get bored with the game, because you’ve seen it before.
I’ve read Seth’s short article several times and wondered about myself. I’ve started to recognize these stages in the games that I “play” at work and home. Looking back, I see myself mostly in stage two: caring a lot about the outcome and stressing that things aren’t going well.
More recently, I see myself being able to step into stage three at times: not taking things so personally, being willing to change my behavior and conversation to be more effective. Stage three is certainly less stressful.
Occasionally, I’ve hit stage four and moved on. I felt like I’d learned all that I would and lost interest in continuing. Not giving up in frustration. More like losing interest in continuing to do something at which I already excelled.
Mostly, I wish for more than this. I’d love the passion and enthusiasm of stage two with the lower stress of stage three in a game that avoids the boredom of stage four. Marriage and family can be this way. Work has the potential as well, though the nature of corporations seems to work against it at times.