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Create singleton using GCD's dispatch_once in Objective-C
...er here: instancetype
+ (instancetype)sharedInstance
{
static dispatch_once_t once;
static id sharedInstance;
dispatch_once(&once, ^
{
sharedInstance = [self new];
});
return sharedInstance;
}
+ (Class*)sharedInstance
{
static dispatch_once_t once;
...
How to add http:// if it doesn't exist in the URL?
...hat went on a swim and came back as a fish with the mindset to stop you at all costs from doing and things that might hurt you. There are so many people in the world, and you know, you have this incredible ideas and what you think is missing is motivation, But that is not true. because the way that ...
Why is early return slower than else?
...e a theory for you.
I tried your code and get the same of results, without_else() is repeatedly slightly slower than with_else():
>>> T(lambda : without_else()).repeat()
[0.42015745017874906, 0.3188967452567226, 0.31984281521812363]
>>> T(lambda : with_else()).repeat()
[0.3600984...
Any way to properly pretty-print ordered dictionaries?
...well if you don't care about the order of the keys. Personally, I wish the __repr__ for OrderedDict would produce output like this but preserve the order of the keys.
– ws_e_c421
Sep 24 '15 at 15:54
...
Downloading a picture via urllib and python
...
Note for Python 3 it's actually import urllib.request urllib.request.urlretrieve("http://...jpg", "1.jpg"). It's urlretrieve now as of 3.x.
– user1032613
Mar 16 '18 at 0:18
...
Cron job every three days
...
The answer is not correct because neither suggestion actually runs the job every 3 days. 0 0 */3 * * means run on the 1st, 4th, 7th, etc. (*/3 means 1-31/3 means 1,4,7...31) so the gap will be smaller at the end of the month. (It'll run 2 days in a row if the previous month had 3...
How to specify new GCC path for CMake
... path /usr/bin/gcc . But it is old, I need a new version of gcc. So I install a new version in a new path /usr/local/bin/gcc .
...
Understanding Apache's access log
...the client IP)
%l is the identity of the user determined by identd (not usually used since not reliable)
%u is the user name determined by HTTP authentication
%t is the time the request was received.
%r is the request line from the client. ("GET / HTTP/1.0")
%>s is the status code sent from the s...
How to do parallel programming in Python?
For C++, we can use OpenMP to do parallel programming; however, OpenMP will not work for Python. What should I do if I want to parallel some parts of my python program?
...
What's wrong with nullable columns in composite primary keys?
...
Primary keys are for uniquely identifying rows. This is done by comparing all parts of a key to the input.
Per definition, NULL cannot be part of a successful comparison. Even a comparison to itself (NULL = NULL) will fail. This means a key containing NULL would not work.
Additonally, NULL is al...