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What does the explicit keyword mean?
...
The compiler is allowed to make one implicit conversion to resolve the parameters to a function. What this means is that the compiler can use constructors callable with a single parameter to convert from one type to another in order to get t...
Class does not implement its superclass's required members
... I updated to Xcode 6 beta 5 today and noticed I received errors in nearly all of my subclasses of Apple's classes.
4 Answe...
Interfaces — What's the point?
...ntract. A set of public methods any implementing class has to have. Technically, the interface only governs syntax, i.e. what methods are there, what arguments they get and what they return. Usually they encapsulate semantics as well, although that only by documentation.
You can then have differen...
MongoDB atomic “findOrCreate”: findOne, insert if nonexistent, but do not update
...: { _id: "some potentially existing id" },
update: {
$setOnInsert: { foo: "bar" }
},
new: true, // return new doc if one is upserted
upsert: true // insert the document if it does not exist
})
As $setOnInsert only affects documents being inserted, if an existing document is found, no...
Is it pythonic to import inside functions?
...at it needs to import.
If I'm adding new code to an existing file I'll usually do the import where it's needed and then if the code stays I'll make things more permanent by moving the import line to the top of the file.
One other point, I prefer to get an ImportError exception before any code is r...
Defining a variable with or without export
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Specifically export makes the variable available to child processes via the environment.
– Beano
Jul 21 '09 at 13:35
...
Collapse sequences of white space into a single character and trim string
...low, because it creates a new object for every substring and sends method calls to each of them.
– Georg Schölly
Jun 23 '11 at 18:55
2
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Can I list-initialize a vector of move-only type?
...nitializer list elements in the current revision of the language.
Specifically, we have:
typedef const E& reference;
typedef const E& const_reference;
typedef const E* iterator;
typedef const E* const_iterator;
const E* begin() const noexcept; // first element
const E* end() const noexce...
What's wrong with overridable method calls in constructors?
...ohibit it:
There are a few more restrictions that a class must obey to allow inheritance. Constructors must not invoke overridable methods, directly or indirectly. If you violate this rule, program failure will result. The superclass constructor runs before the subclass constructor, so the overr...
How to 'bulk update' with Django?
...ings like incrementing rows:
from django.db.models import F
Entry.objects.all().update(n_pingbacks=F('n_pingbacks') + 1)
See the documentation.
However, note that:
This won't use ModelClass.save method (so if you have some logic inside it won't be triggered).
No django signals will be emitte...