useful_extension

Integrate other languages (like Java and Kotlin) code style to extensions.

Java Util Function Extension

Dart Class	Java Class	Dart Prototype
Consumer<T>	Consumer<T>	void Function(T)
Predicate<T>	Predicate<T>	bool Function(T)
Action	Action	void Function()
Supplier<R>	Supplier<R>	R Function()
Transformer<T, R>	Function<T, R>	R Function(T)
BiConsumer<T, U>	BiConsumer<T, U>	void Function(T, U)
BiPredicate<T, U>	BiPredicate<T, U>	bool Function(T, U)
BiTransformer<T, U, R>	BiFunction<T, U, R>	R Function(T, U)

Kotlin Style Extension

Operator	Parameter	Returns
let	self	self
apply	-	self
also	self	R
run	-	R

Simple Usage

String name = null;
name?.let((it){
  print("it=$it");
});

Because name is null, so let not execute.

String name = "Hello";
name?.let((it){
  print("it=$it");
});

Because name is not null, so outputs "it=Hello".

Use to Initialize Instance

By cascade style

People john = People()
  ..name = "John"
  ..age = 18;

By let operator

People john = People().let((it) {
  it.name = "John";
  it.age = 18;
});

Operator Chains

100.also((it) => it * it)
   .also((it) => it.toString())
   .also((it) => double.parse(it))
   .let((it) => print("result=$it"));

Functions Invocation

You can call invoke to execute a Function.

Dart style Function execution

Function func = () => print("Execute");
func();

Use invoke instead of Dart style execution

Function func = () => print("Execute");
func.invoke();

Use invoke and let to Simplified Null Safety Style

Dart style Function null safety

Function func = null;
if(func != null) func();

Instead of invoke and let style

Function func = null;
func?.invoke();

invoke also Supports Parameters and Returns

Parameters and returns will auto transform and keep type-safe.

typedef Func1 = bool Function(String s, int i);
typedef Func2 = String Function(int i);

Func1 func1 = null;
bool result1 = func1?.invoke("String", 100);

Func2 func2 = null;
String result2 = func2?.invoke(100);

func2?.invoke(true); /// compile error
bool r = func2?.invoke(100); /// compile errpr

Kotlin Collection Extension

Iterable<E>

Property	Type	R/W
lastIndex	int	R

Return Type	Method
Iterable<IndexedValue>	withIndex()
Iterable<E>	whereNot(bool test(E element))
Iterable<int>	indexes()
E	elementAtOr(int index, [E defaultValue = null])
E	firstOr([E defaultValue = null])
E	lastOr([E defaultValue = null])

Dart Basic Extension

Operator cast

Use cast instead of as to make chain style.

dynamic o = "Hello";
(o as String).length;
o.cast<String>().length;

((o as String) as String).length;
o.cast<String>().cast<String>().length;

Futures