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insert vs emplace vs operator[] in c++ map
...maps.)
Here's an example to demonstrate:
#include <vector>
struct foo
{
explicit foo(int);
};
int main()
{
std::vector<foo> v;
v.emplace(v.end(), 10); // Works
//v.insert(v.end(), 10); // Error, not explicit
v.insert(v.end(), foo(10)); // Also works
}
...
How do I check for nulls in an '==' operator overload without infinite recursion?
...
Use ReferenceEquals:
Foo foo1 = null;
Foo foo2 = new Foo();
Assert.IsFalse(foo1 == foo2);
public static bool operator ==(Foo foo1, Foo foo2) {
if (object.ReferenceEquals(null, foo1))
return object.ReferenceEquals(null, foo2);
ret...
Try-finally block prevents StackOverflowError
...(2^N) where N is the maximum stack depth.
Imagine the maximum depth is 5
foo() calls
foo() calls
foo() calls
foo() calls
foo() which fails to call foo()
finally calls
foo() which fails to call foo()
finally
foo() calls
...
How to use C++ in Go
... have inheritance.
Here's an example:
I have a C++ class defined as:
// foo.hpp
class cxxFoo {
public:
int a;
cxxFoo(int _a):a(_a){};
~cxxFoo(){};
void Bar();
};
// foo.cpp
#include <iostream>
#include "foo.hpp"
void
cxxFoo::Bar(void){
std::cout<<this->a<<std::endl...
C# generic type constraint for everything nullable
...
If you are willing to make a runtime check in Foo's constructor rather than having a compile-time check, you can check if the type is not a reference or nullable type, and throw an exception if that's the case.
I realise that only having a runtime check may be unaccepta...
How to create an object for a Django model with a many to many field?
...ginal suggestion. It works, but isn't optimal. (Note: I'm using Bars and a Foo instead of Users and a Sample, but you get the idea).
bar1 = Bar.objects.get(pk=1)
bar2 = Bar.objects.get(pk=2)
foo = Foo()
foo.save()
foo.bars.add(bar1)
foo.bars.add(bar2)
It generates a whopping total of 7 queries:
...
What is the colon operator in Ruby?
...
:foo is a symbol named "foo". Symbols have the distinct feature that any two symbols named the same will be identical:
"foo".equal? "foo" # false
:foo.equal? :foo # true
This makes comparing two symbols really fast (sin...
How to disallow temporaries
For a class Foo, is there a way to disallow constructing it without giving it a name?
10 Answers
...
Looping over arrays, printing both index and value
...
You would find the array keys with "${!foo[@]}" (reference), so:
for i in "${!foo[@]}"; do
printf "%s\t%s\n" "$i" "${foo[$i]}"
done
Which means that indices will be in $i while the elements themselves have to be accessed via ${foo[$i]}
...
How to decorate a class?
...
Example:
def substitute_init(self, id, *args, **kwargs):
pass
class FooMeta(type):
def __new__(cls, name, bases, attrs):
attrs['__init__'] = substitute_init
return super(FooMeta, cls).__new__(cls, name, bases, attrs)
class Foo(object):
__metaclass__ = FooMeta
d...