Tutorial by Examples: construct

(This is a request for a good example that shows how to construct a SELECT using CONCAT, then prepare+execute it. Please emphasize the use of @variables versus DECLAREd variables -- it makes a big difference, and it is something that novices (include myself) stumble over.)
Value constructors are functions that return a value of a data type. Because of this, just like any other function, they can take one or more parameters: data Foo = Bar String Int | Biz String Let's check the type of the Bar value constructor. :t Bar prints Bar :: String -> Int -> Foo...
In D we can use constructors to initialize structs just like a class. To define a construct for the struct declared in the previous example we can type: struct Person { this(int age, int height) { this.age = age; this.height = height; this.ageXHeight = cast(float)age...
Example: Invoke different constructors by passing relevant parameters import java.lang.reflect.*; class NewInstanceWithReflection{ public NewInstanceWithReflection(){ System.out.println("Default constructor"); } public NewInstanceWithReflection( String a){ ...
All constructors in Java must make a call to the Object constructor. This is done with the call super(). This has to be the first line in a constructor. The reason for this is so that the object can actually be created on the heap before any additional initialization is performed. If you do not spe...
Classes without dependencies can easily be created by dagger. public class Engine { @Inject // <-- Annotate your constructor. public Engine() { } } This class can be provided by any component. It has no dependencies itself and is not scoped. There is no further code necessar...
If you want to create an instance of an inner nested class you need to provide a class object of the enclosing class as an extra parameter with Class#getDeclaredConstructor. public class Enclosing{ public class Nested{ public Nested(String a){ System.out.println("Constru...
Well, if you want a switch/case construct, the most straightforward way to go is to use the good old if/else construct: def switch(value): if value == 1: return "one" if value == 2: return "two" if value == 42: return "the answer to...
If the type on which the static constructor is declared is generic, the static constructor will be called once for each unique combination of generic arguments. class Animal<T> { static Animal() { Console.WriteLine(typeof(T).FullName); } public static void Yawn...
If a static constructor throws an exception, it is never retried. The type is unusable for the lifetime of the AppDomain. Any further usages of the type will raise a TypeInitializationException wrapped around the original exception. public class Animal { static Animal() { Consol...
x IN ( SELECT ... ) turn into a JOIN When possible, avoid OR. Do not 'hide' an indexed column in a function, such as WHERE DATE(x) = ...; reformulate as WHERE x = ... You can generally avoid WHERE LCASE(name1) = LCASE(name2) by having a suitable collation. Do no use OFFSET for "paginatio...
A very useful feature many people overlook is the ability to construct a Map using a SOQL query. Map<Id, Account> accounts = new Map<Id, Account>([SELECT Id, Name FROM Account]); System.debug(accounts); When you run this code, accounts then contains a Map of your Account objects, ke...
The $q constructor function is used to create promises from asynchronous APIs that use callbacks to return results. $q(function(resolve, reject) {...}) The constructor function receives a function that is invoked with two arguments, resolve and reject that are functions which are used to eithe...
We can create a Map from a list of tuples like this: Map.fromList [("Alex", 31), ("Bob", 22)] A Map can also be constructed with a single value: > Map.singleton "Alex" 31 fromList [("Alex",31)] There is also the empty function. empty :: Map k a ...
Constructors are special methods named after the class and without a return type, and are used to construct objects. Constructors, like methods, can take input parameters. Constructors are used to initialize objects. Abstract classes can have constructors also. public class Hello{ // construct...
Prior to C++17, template deduction cannot deduce the class type for you in a constructor. It must be explicitly specified. Sometimes, however, these types can be very cumbersome or (in the case of lambdas) impossible to name, so we got a proliferation of type factories (like make_pair(), make_tuple(...
Enum constructors can be matched using pattern matching. Assume the following enum: enum Color { Red; Green; Blue; RGB(r : Int, g : Int, b : Int); } Colours with only a green channel value can be matched as follows: var color = Color.RGB(0, 127, 0); var isGreenOnly = swit...
The Standard (10.4) states: Member functions can be called from a constructor (or destructor) of an abstract class; the effect of making a virtual call (10.3) to a pure virtual function directly or indirectly for the object being created (or destroyed) from such a constructor (or destructor) is u...
Sometimes you have to deal with structures defined in terms of C data types from Perl. One such application is the creation of raw network packets, in case you want to do something fancier than what the regular socket API has to offer. This is just what pack() (and unpack() of course) is there for. ...
The behaviour of virtual functions in constructors and destructors is often confusing when first encountered. #include <iostream> using namespace std; class base { public: base() { f("base constructor"); } ~base() { f("base destructor"); } virtual co...

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