What is the use of curly braces in Dart method signature

dart function type
dart generic class
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dart named parameters
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class TapboxA extends StatefulWidget {

 TapboxA({Key key}) : super(key: key);

}

This part :

TapboxA({Key key}) 

The second half

super(key: key);

I understand, (a call to super class constructor).

But what is the

{Key key}

syntax doing?

In Dart constructors ( and other methods ) can have optional named parameters :

MyClass({String namedParam}){//...}

In the case of a Flutter widget constructor :

TapboxA({Key key})  // TapboxA constructor defines a named parameters `key`
: super(key: key); //which is used within the super constructor call (which also has `key` as named parameter )

You can find more information about optional named parameters in the Dart language tour

What is the use of curly braces in Dart method signature, A common case is the result of a null-aware method call being used as a condition: if (optionalThing? AVOID using curly braces in interpolation when not needed. Linter rule: For consistency with optional positional parameters, use = . Dart Constructor using Curly braces: Named optional parameters. We can also definie a constructor using curly braces { } to specify named parameters.

Dart provides an option on constructors. By default, when you instantiate a class with a constructor you are forced to provide the parameters defined.

Therefore, TapboxA({Key key}) means you can instantiate the class without providing the arguments.

Effective Dart: Usage, The following code uses many of Dart's most basic features: // Define a function. printInteger(int aNumber) { print('The number is $aNumber.'); // Print to console. }​  A surprisingly important part of good code is good style. Consistent naming, ordering, and formatting helps code that is the same look the same. It takes advantage of the powerful pattern-matching hardware most of us have in our ocular systems. If we use a consistent style across the entire Dart ecosystem, it makes it

It's not something special with constructors only.

For all Dart methods we have the option of named arguments as in languages like Python

Using a curly brace syntax, you can define optional parameters that have names.

So with the method signature using the curly braces,

TapboxA({Key key}) :

you can call this constructor in two different ways

The usual method, without named parameter

tapboxA1 = TapboxA(keyObject)

The extra nicety of named parameter

tapboxA2 = TapboxA(key: keyObject)

In other words the usefulness comes at the time of calling the method, not in the method itself.

Language tour, How do you pass a function as a parameter in darts? PREFER an imperative verb phrase for a function or method whose main purpose is a side effect. PREFER a noun phrase or non-imperative verb phrase for a function or method if returning a value is its primary purpose. CONSIDER an imperative verb phrase for a function or method if you want to draw attention to the work it performs.

Void class - dart:ffi library - Dart API, code and serves purely as marker in type signatures. If you do choose to use part to split part of a library out into another file, Dart requires the other file to in turn indicate which library it’s a part of. For legacy reasons, Dart allows this part of directive to use the name of the library it’s a part of.

Dart (DartLang) Introduction: Advanced Dart Features, . Dart provides factory keyword to label a default or named constructor. Then it becomes our responsibility to return an instance from this constructor. A factor constructor is generally used to control the instance creation. Within any class or method, the code between a pair of curly braces is called a(n) ____. block An alternative to importing a class is to import an entire package of classes.

Learning Functions for Dart, Which is the correct form of shorthand function in DART? The client can use a method without knowing how it is implemented. The details of the implementation are encapsulated in the method and hidden from the client who invokes the method. This is known as _____. A. information hiding B. encapsulation C. method hiding D. simplifying method

Comments
  • Where is the value of "key" obtained from? I see this code in widget "child: new TapboxA()," with no value for the named parameter supplied....
  • @SirPaulMuaddib It's because optional parameters are optional :)
  • @SirPaulMuaddib Keys are used for a fined-grained control over Widgets rebuilds. In a infinite scroll list you are able to avoid full rebuild of the entire list by assigning to its items a key, as new items are added to list, the previous ones aren't rebuilt unless its Key, along with its runtimType matches: flutter.io/widgets-intro/#keys