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Designing function f(f(n)) == -n
...oof of why such a function can't exist, for all numbers, if it doesn't use extra information(except 32bits of int):
We must have f(0) = 0. (Proof: Suppose f(0) = x. Then f(x) = f(f(0)) = -0 = 0. Now, -x = f(f(x)) = f(0) = x, which means that x = 0.)
Further, for any x and y, suppose f(x) = y. We w...
How would I create a UIAlertView in Swift?
...should only be used when UIAlertController is not available. if NSClassFromString("UIAlertController") != nil { /* use UIAlertController * / } else { /* use UIAlertView * / }
– phatblat
Apr 16 '15 at 17:01
...
Why is “if not someobj:” better than “if someobj == None:” in Python?
...test for equality when you want to compare objects of the same nature (two strings, two numbers, ...) and to check for identity only when using sentinel values (None meaning not initialized for a member field for exemple, or when using the getattr or the __getitem__ methods).
To summarize, we have ...
Rails Root directory path?
... 3 and newer:
Rails.root
which returns a Pathname object. If you want a string you have to add .to_s. If you want another path in your Rails app, you can use join like this:
Rails.root.join('app', 'assets', 'images', 'logo.png')
In Rails 2 you can use the RAILS_ROOT constant, which is a string...
C# member variable initialization; best practice?
...d properties (field initializers cannot) - i.e.
[DefaultValue("")]
public string Foo {get;set;}
public Bar() { // ctor
Foo = "";
}
Other than that, I tend to prefer the field initializer syntax; I find it keeps things localized - i.e.
private readonly List<SomeClass> items = new List<...
Using Excel OleDb to get sheet names IN SHEET ORDER
...param name="excelFile">The excel file.</param>
/// <returns>String[]</returns>
private String[] GetExcelSheetNames(string excelFile)
{
OleDbConnection objConn = null;
System.Data.DataTable dt = null;
try
{
// Connection String. Change the excel file to t...
How to test code dependent on environment variables using JUnit?
...onmentVariablesTest {
@Test
public void setEnvironmentVariable() {
String value = withEnvironmentVariable("name", "value")
.execute(() -> System.getenv("name"));
assertEquals("value", value);
}
}
For Java 5 to 7 the library System Rules has a JUnit rule called EnvironmentVari...
How to check if an object is a list or tuple (but not string)?
...
In python 2 only (not python 3):
assert not isinstance(lst, basestring)
Is actually what you want, otherwise you'll miss out on a lot of things which act like lists, but aren't subclasses of list or tuple.
share...
jQuery callback on image load (even when the image is cached)
...
/**
* Trigger a callback when the selected images are loaded:
* @param {String} selector
* @param {Function} callback
*/
var onImgLoad = function(selector, callback){
$(selector).each(function(){
if (this.complete || /*for IE 10-*/ $(this).height() > 0) {
callback.ap...
Android: Getting a file URI from a content URI?
...n use the Content Resolver to get a file:// path from the content:// URI:
String filePath = null;
Uri _uri = data.getData();
Log.d("","URI = "+ _uri);
if (_uri != null && "content".equals(_uri.getScheme())) {
Cursor cursor = this.getContentResolver...