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Checking if a variable is defined?
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Use the defined? keyword (documentation). It will return a String with the kind of the item, or nil if it doesn’t exist.
>> a = 1
=> 1
>> defined? a
=> "local-variable"
>> defined? b
=> nil
>> defined? nil
=> "nil"
>> ...
Is there more to an interface than having the correct methods
...e you want to use a different kind of box (maybe there's another library, with a better kind of box), you switch your code to:
Ibox myBox=new OtherKindOfBox();
Once you get used to it, you'll find it's a great (actually essential) way to work.
Another reason is, for example, if you want to creat...
Can I get “&&” or “-and” to work in PowerShell?
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In CMD, '&&' means "execute command 1, and if it succeeds, execute command 2". I have used it for things like:
build && run_tests
In PowerShell, the closest thing you can do is:
(build) -and (run_tests)
It has the same logic, but the output text from the c...
Are there legitimate uses for JavaScript's “with” statement?
Alan Storm's comments in response to my answer regarding the with statement got me thinking. I've seldom found a reason to use this particular language feature, and had never given much thought to how it might cause trouble. Now, I'm curious as to how I might make effective use of with , while a...
Why are primes important in cryptography?
One thing that always strikes me as a non-cryptographer: Why is it so important to use Prime numbers? What makes them so special in cryptography?
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JavaScript: filter() for Objects
...e. Things will break. You're extending all object types, including object literals.
Here's a quick example you can try:
// Extend Object.prototype
Object.prototype.extended = "I'm everywhere!";
// See the result
alert( {}.extended ); // "I'm everywhere!"
alert( [].extended ); ...
Storing Data in MySQL as JSON
I thought this was a n00b thing to do. And, so, I've never done it. Then I saw that FriendFeed did this and actually made their DB scale better and decreased latency. I'm curious if I should do this. And, if so, what's the right way to do it?
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How to create a memory leak in Java?
I just had an interview, and I was asked to create a memory leak with Java.
Needless to say, I felt pretty dumb having no clue on how to even start creating one.
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Set width of a “Position: fixed” div relative to parent div
I'm trying to give a div (position: fixed) the width of 100% (relating to it's parent div). But I've got some problems...
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How do you properly determine the current script directory in Python?
...name(os.path.abspath(__file__))
is indeed the best you're going to get.
It's unusual to be executing a script with exec/execfile; normally you should be using the module infrastructure to load scripts. If you must use these methods, I suggest setting __file__ in the globals you pass to the script...