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Performance surprise with “as” and nullable types
...d is of the expected type, takes but a few machine code instructions. The cast is also easy, the JIT compiler knows the location of the value bits in the object and uses them directly. No copying or conversion occurs, all machine code is inline and takes but about a dozen instructions. This neede...
How does std::move() transfer values into RValues?
...reference<T>::type&& move(T&& arg)
{
return static_cast<typename remove_reference<T>::type&&>(arg);
}
Let's start with the easier part - that is, when the function is called with rvalue:
Object a = std::move(Object());
// Object() is temporary, which ...
How to make a select with array contains value clause in psql
...
Try
SELECT * FROM table WHERE arr @> ARRAY['s']::varchar[]
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What is 'Pattern Matching' in functional languages?
...s similar to dynamic message dispatch) but I can't see how at run-time you select a branch without a type test.
– David Moles
Feb 17 '16 at 23:42
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Is the LIKE operator case-sensitive with MSSQL Server?
...en-us/library/ms144250(v=sql.105).aspx
(a) To check a instance collation
select serverproperty('collation')
(b) To check a database collation
select databasepropertyex('databasename', 'collation') sqlcollation
(c) To create a database using a different collation
create database exampledataba...
Cast an instance of a class to a @protocol in Objective-C
... [vc protocolMethod];
}
The UIViewController <MyProtocol> * type-cast translates to "vc is a UIViewController object that conforms to MyProtocol", whereas using id <MyProtocol> translates to "vc is an object of an unknown class that conforms to MyProtocol".
This way the compiler wil...
Most efficient T-SQL way to pad a varchar on the left to a certain length?
...cely. It will also perform the conversion for you:
declare @n as int = 2
select FORMAT(@n, 'd10') as padWithZeros
Update:
I wanted to test the actual efficiency of the FORMAT function myself. I was quite surprised to find the efficiency was not very good compared to the original answer from Al...
Converting bool to text in C++
...Boost that can help us out here. Boost has a nice function called lexical_cast. We can use it thus:
boost::lexical_cast<std::string>(my_bool)
Now, it's true to say that this is higher overhead than some macro; stringstreams deal with locales which you might not care about, and create a dy...
Does the 'mutable' keyword have any purpose other than allowing the variable to be modified by a con
....
Without the mutable keyword you will eventually be forced to use const_cast to handle the various useful special cases it allows (caching, ref counting, debug data, etc.). Unfortunately const_cast is significantly more destructive than mutable because it forces the API client to destroy the cons...
What is the difference between ExecuteScalar, ExecuteReader and ExecuteNonQuery?
... then the result is the first column of the first row. An example might be SELECT @@IDENTITY AS 'Identity'.
ExecuteReader is used for any result set with multiple rows/columns (e.g., SELECT col1, col2 from sometable).
ExecuteNonQuery is typically used for SQL statements without results (e.g., UPDATE...