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C++ templates that accept only certain types
...
I suggest using Boost's static assert feature in concert with is_base_of from the Boost Type Traits library:
template<typename T>
class ObservableList {
BOOST_STATIC_ASSERT((is_base_of<List, T>::value)); //Yes, the double parentheses are needed, otherwise the comma will be...
Round to 5 (or other number) in Python
...ndard function in Python, 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 integ...
Algorithms based on number base systems? [closed]
I've noticed recently that there are a great many algorithms out there based in part or in whole on clever uses of numbers in creative bases. For example:
...
new keyword in method signature
...:
You cannot override a non-virtual or
static method. The overridden base
method must be virtual, abstract, or
override.
So the 'new' keyword is needed to allow you to 'override' non-virtual and static methods.
s...
Downcasting shared_ptr to shared_ptr?
...amic_pointer_cast. It is supported by std::shared_ptr.
std::shared_ptr<Base> base (new Derived());
std::shared_ptr<Derived> derived =
std::dynamic_pointer_cast<Derived> (base);
Documentation: https://en.cppreference.com/w/cpp/memory/shared_ptr/pointer_cast
Also, ...
How to use base class's constructors and assignment operator in C++?
...
You can explicitly call constructors and assignment operators:
class Base {
//...
public:
Base(const Base&) { /*...*/ }
Base& operator=(const Base&) { /*...*/ }
};
class Derived : public Base
{
int additional_;
public:
Derived(const Derived& d)
: Base(d...
What is the point of a private pure virtual function?
... classes. Methods of derived classes can't call virtual functions from the base class, but they can provide their own implementation for them. According to Herb Sutter, having public non-virtual interface in the base class and a private implementation that can be customized in the derived classes, a...
The most efficient way to implement an integer based power function pow(int, int)
...
Exponentiation by squaring.
int ipow(int base, int exp)
{
int result = 1;
for (;;)
{
if (exp & 1)
result *= base;
exp >>= 1;
if (!exp)
break;
base *= base;
}
return result;
}
Th...
Calling virtual functions inside constructors
...om derived classes hasn’t yet happened. Objects are constructed from the base up, “base before derived”.
[...]
Destruction is done “derived class before base class”, so virtual functions behave as in constructors: Only the local definitions are used – and no calls are made to overriding ...
How to solve error “Missing `secret_key_base` for 'production' environment” (Rails 4.1)
...icorn.log file I found this error message:
app error: Missing `secret_key_base` for 'production' environment, set this value in `config/secrets.yml` (RuntimeError)
After some research I found out that Rails 4.1 changed the way to manage the secret_key, so if you read the secrets.yml file located ...