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Rails migration for change column
...l situations where the existing data, let's say a String can be implicitly converted into the new datatype, let's say Date.
In this situation, it's helpful to know you can create migrations with data conversions. Personally, I like putting these in my model file, and then removing them after all d...
What are some uses of template template parameters?
...he exact type explicitly.
which you can use like this:
f<std::vector, int>(v); // v is of type std::vector<int> using any allocator
or better yet, we can just use:
f(v); // everything is deduced, f can deal with a vector of any type!
UPDATE: Even this contrived example, while illu...
What is the best way to find the users home directory in Java?
...\Application Data (CSIDL_LOCAL_APPDATA).
Sample JNA code:
public class PrintAppDataDir {
public static void main(String[] args) {
if (com.sun.jna.Platform.isWindows()) {
HWND hwndOwner = null;
int nFolder = Shell32.CSIDL_LOCAL_APPDATA;
HANDLE hToken...
Round to 5 (or other number) in Python
...thon, but this works for me:
Python 2
def myround(x, base=5):
return int(base * round(float(x)/base))
Python3
def myround(x, base=5):
return base * round(x/base)
It is easy to see why the above works. You want to make sure that your number divided by 5 is an integer, correctly rounde...
Java: method to get position of a match in a String?
...
The family of methods that does this are:
int indexOf(String str)
indexOf(String str, int fromIndex)
int lastIndexOf(String str)
lastIndexOf(String str, int fromIndex)
Returns the index within this string of the first (or last) occurrence of the specified ...
Getting View's coordinates relative to the root layout
...swers. One claims to be faster, and another claims to be easier.
private int getRelativeLeft(View myView) {
if (myView.getParent() == myView.getRootView())
return myView.getLeft();
else
return myView.getLeft() + getRelativeLeft((View) myView.getParent());
}
private int get...
Which, if any, C++ compilers do tail-recursion optimization?
... done for more than a decade), even for mutually recursive calls such as:
int bar(int, int);
int foo(int n, int acc) {
return (n == 0) ? acc : bar(n - 1, acc + 2);
}
int bar(int n, int acc) {
return (n == 0) ? acc : foo(n - 1, acc + 1);
}
Letting the compiler do the optimisation is stra...
Android, ListView IllegalStateException: “The content of the adapter has changed but ListView did no
...hers to refer.
My loader on the main screen loads the phone book contacts into my data sources in the background.
@Override
public Void loadInBackground() {
Log.v(TAG, "Init loadings contacts");
synchronized (SingleTonProvider.getInstance()) {
PhoneBookManager.p...
C# Object Pooling Pattern implementation
...Pool<T>
{
public static ArrayPool<T> Shared { get; internal set; }
public static ArrayPool<T> Create(int maxBufferSize = <number>, int numberOfBuffers = <number>);
public T[] Rent(int size);
public T[] Enlarge(T[] buffer, int newSi...
C default arguments
...al argument that may be present depending on the required arguments, and printf(3) reads a format string that specifies how many arguments there will be. Both use varargs quite safely and effectively, and though you can certainly screw them up, printf() especially seems to be quite popular.
...