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Hidden features of C
...ints to the compiler (common in the Linux kernel)
#define likely(x) __builtin_expect((x),1)
#define unlikely(x) __builtin_expect((x),0)
see: http://kerneltrap.org/node/4705
What I like about this is that it also adds some expressiveness to some functions.
void foo(int arg)
{
if (...
List of lists changes reflected across sublists unexpectedly
...at you create a new list at each position. One way to do it is
[[1]*4 for _ in range(3)]
which will reevaluate [1]*4 each time instead of evaluating it once and making 3 references to 1 list.
You might wonder why * can't make independent objects the way the list comprehension does. That's beca...
What does |= (ior) do in Python?
...s1 |= s2 # 2
>>> s1.__ior__(s2) # 3
where the final value of s1 is equivalent either by:
an assigned OR operation
an in-place OR operation
an in-place OR operation via special method++
Example
Here we a...
What's the difference between the atomic and nonatomic attributes?
... variables; they will be synthesized automatically, too, and will have an _ prepended to their name to prevent accidental direct access).
With "atomic", the synthesized setter/getter will ensure that a whole value is always returned from the getter or set by the setter, regardless of setter activi...
How to access object attribute given string corresponding to name of that attribute
...ay prefer to use a generalized getter method like so:
class Test:
def __init__(self):
self.attr1 = 1
self.attr2 = 2
def get(self,varname):
return getattr(self,varname)
t = Test()
x = "attr1"
print ("Attribute value of {0} is {1}".format(x, t.get(x)))
Outputs:
At...
Weak and strong property setter attributes in Objective-C
...n release autorelease etc... Instead you use strong weak for properties or __strong
__weak
for variables (defaults to __strong). Strong is the equivalent to retain, however ARC will manage the release for you.
The only time you would want to use weak, is if you wanted to avoid retain cycles (e.g...
Hide keyboard when scroll UITableView
...to our UITableViewController class
override func scrollViewDidScroll(_ scrollView: UIScrollView) {
if !tableView.isDecelerating {
view.endEditing(true)
}
}
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Why is there no xrange function in Python3?
...tion has nothing to do with it. (Not surprising, as a one-time call to the __iter__ slot isn't likely to be visible among 10000000 calls to whatever happens in the loop, but someone brought it up as a possibility.)
But it's only 30% slower. How did the OP get 2x as slow? Well, if I repeat the same ...
Running python script inside ipython
...
from within the directory of "my_script.py" you can simply do:
%run ./my_script.py
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Are HLists nothing more than a convoluted way of writing tuples?
...)
// Publish their `HListIso`'s
implicit def fooIso = Iso.hlist(Foo.apply _, Foo.unapply _)
implicit def barIso = Iso.hlist(Bar.apply _, Bar.unapply _)
// And now they're monoids ...
implicitly[Monoid[Foo]]
val f = Foo(13, "foo") |+| Foo(23, "bar")
assert(f == Foo(36, "foobar"))
implicitly[Monoi...