js设计模式之BehavioralPatterns之Iterator
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2022-10-19 13:46:59
class KingSuccession {
constructor(inLineForThrone){
this.inLineForThrone...
class KingSuccession { constructor(inLineForThrone){ this.inLineForThrone = inLineForThrone; this.pointer = 0; } next(){ return this.inLineForThrone[this.pointer++]; } } var kin = new KingSuccession(["Robert Baratheon","JofferyBaratheon","TommenBaratheon"]); kin.next(); kin.next(); kin.next();
An interesting application of iterators is to not iterate over a fixed collection. For
instance an iterator can be used to generate sequential members of an infinite set
like the fibonacci sequence:
class FibonacciIterator{ constructor(){ this.previous = 1; this.beforePrevious = 1; } next(){ var current = this.previous + this.beforePrevious; this.beforePrevious = this.previous; this.previous = current; return current; } } var fib = new FibonacciIterator(); fib.next(); fib.next(); fib.next();
Iterators are a syntactic nicety that has long been missing from Script. Another
great feature of ECMAScript-2015 are generators. This is, in effect, a built in iterator
factory. Our fibonacci sequence could be rewritten like the following:
function* FibonacciGenerator () { var previous = 1; var beforePrevious = 1; while (true){ var current = previous + beforePrevious; beforePrevious = previous; previous = current; yield current; } } var fibo = new FibonacciGenerator(); fibo.next().value; fibo.next().value; fibo.next().value;
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