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Double negation (!!) in javascript - what is the purpose? [duplicate]
...
It casts to boolean. The first ! negates it once, converting values like so:
undefined to true
null to true
+0 to true
-0 to true
'' to true
NaN to true
false to true
All other expressions to false
Then the other ! negates i...
Concatenate multiple result rows of one column into one, group by another column [duplicate]
...ase.
string_agg() expects data type text as input. Other types need to be cast explicitly (actor::text) - unless an implicit cast to text is defined - which is the case for all other character types (varchar, character, "char"), and some other types.
As isapir commented, you can add an ORDER BY c...
c++11右值引用、std::move移动语义、std::forward完美转发的一些总结 - C/C...
...语义。从实现上讲，它基本等同于一个类型转换：static_cast<T&&>(lvalue);特别
std::move 实际上并不能移动任何东西，它唯一的功能是将一个左值强制转换为右值引用，继而用于移动语义。从实现上讲，它基本等同于一个类型转换...
Is null an Object?
...no
name, it is impossible to declare a
variable of the null type or to cast
to the null type. The null reference
is the only possible value of an
expression of null type. The null
reference can always be cast to any
reference type. In practice, the
programmer can ignore the null type...
Count the items from a IEnumerable without iterating?
...enumerator.MoveNext())
result++;
}
return result;
So it tries to cast to ICollection<T>, which has a Count property, and uses that if possible. Otherwise it iterates.
So your best bet is to use the Count() extension method on your IEnumerable<T> object, as you will get the bes...
How to call base.base.method()?
...
Nevermind, figured it out. Cast to Func<stuff> instead of Action
– Perkins
Sep 1 '18 at 4:14
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Why is (object)0 == (object)0 different from ((object)0).Equals((object)0)?
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When you cast the int value 0 (or any other value type) to object, the value is boxed. Each cast to object produces a different box (i.e. a different object instance). The == operator for the object type performs a reference compariso...
java: HashMap not working
...s aren't retained at runtime. They are just "syntactic sugar" for explicit casting to save you doing this:
Integer i = (Integer)myMap.get("foo");
To give you an example, this code is perfectly legal:
Map<String, Integer> myMap = new HashMap<String, Integer>();
Map<Integer, String&...
Timer function to provide time in nano seconds using C++
..."rdtsc" : "=a" (lo), "=d" (hi));
return time_point(duration(static_cast<rep>(hi) << 32 | lo));
}
};
} // x
All this clock does is count CPU cycles and store it in an unsigned 64-bit integer. You may need to tweak the assembly language syntax for your compiler. Or your c...
What does T&& (double ampersand) mean in C++11?
...t[]> ptr2{ptr1};// compile error: no copy ctor.
// So we must first cast ptr1 to an rvalue
std::unique_ptr<int[]> ptr2{std::move(ptr1)};
std::unique_ptr<int[]> TakeOwnershipAndAlter(std::unique_ptr<int[]> param,\
int size)
{
for (auto i = 0; i < size; ++i) {...