use deque in tail and trunc implementations

make-github-pseudonymous-again · Jul 27, 2016 · 9716cbc · 9716cbc
1 parent f81f9d5
commit 9716cbc
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Showing 3 changed files with 15 additions and 26 deletions.
diff --git a/src/base/tail.js b/src/base/tail.js
@@ -1,3 +1,5 @@
+import { deque } from 'aureooms-js-collections' ;
+
 import { iter } from './iter' ;
 import { drop } from './drop' ;
 
@@ -21,25 +23,6 @@ export function* tail ( iterable , n ) {
 		return ;
 	}
 
-	const iterator = iter( iterable ) ;
-
-	// use real deque here
-	const buffer = [ ] ;
-
-	while ( n --> 0 ) {
-		const e = iterator.next( ) ;
-		if ( e.done ) {
-			yield* buffer ;
-			return ;
-		}
-		buffer.push( e.value ) ;
-	}
-
-	for ( const value of iterator ) {
-		buffer.push( value ) ;
-		buffer.shift() ;
-	}
-
-	yield* buffer ;
+	yield* deque( iterable , n ) ;
 
 }
diff --git a/src/base/trunc.js b/src/base/trunc.js
@@ -1,3 +1,5 @@
+import { deque } from 'aureooms-js-collections' ;
+
 import { iter } from './iter' ;
 import { take } from './take' ;
 
@@ -21,20 +23,24 @@ export function* trunc ( iterable , n ) {
 		return ;
 	}
 
+	if ( n === 0 ) {
+		yield* iterable ;
+		return ;
+	}
+
 	const iterator = iter( iterable ) ;
 
-	// use real deque here
-	const buffer = [ ] ;
+	const buffer = deque( null , n ) ;
 
 	while ( n --> 0 ) {
 		const e = iterator.next( ) ;
 		if ( e.done ) return ;
-		buffer.push( e.value ) ;
+		buffer.append( e.value ) ;
 	}
 
 	for ( const value of iterator ) {
-		buffer.push( value ) ;
-		yield buffer.shift() ;
+		yield buffer.popleft() ;
+		buffer.append( value ) ;
 	}
 
 }
diff --git a/src/map/permutations.js b/src/map/permutations.js
@@ -41,7 +41,7 @@ export function* permutations ( iterable , r ) {
 
 			if ( cycles[i] === 0 ) {
 
-				// use deque
+				// could be costly
 				indices.push( indices.splice( i , 1 )[0] ) ;
 
 				cycles[i] = len - i ;