Append to string without copy?

Posted on Sat 6th, August 2016

• #1

tve

If I have a long string (say 2KB) is there a way to append to it without causing a second copy of the string to be made? E.g., does str += "more text" cause me to temporarily hold two copies in memory?
• #2

Gordon
I'm pretty sure that str += "more text" will do a proper append automatically as-is, so it should be pretty fast.

If you're interested the code is here

It won't work if the string is referenced elsewhere though:
```
var str = "Hello ";
var foo = str;
str += "more text"; // It's done a copy in this case.
```
• #3

allObjects

...that would be visible in the implementation of +=... This though would mean that the interpreter would know the number of references to the string at the time of concatenation and make the copy if there are more than one references... It all depends how assignments and garbage collect work...

Post a reply
- Bold
- Italics
- Link
- Image
- List
- Quote
- code
- Preview
Formatting Help

Don't worry about formatting, just type in the text and we'll take care of making sense of it. We will auto-convert links, and if you put asterisks around words we will make them bold.

Tips:

Create headers by underlining text with ==== or ----

To *italicise* text put one asterisk each side of the word

To **bold** text put two asterisks each side of the word

Embed images by entering:
![](https://www.google.co.uk/images/srpr/logo4w.png)
That's the hard one: exclamation, square brackets and then the URL to the image in brackets.

* Create lists by starting lines with asterisks

1. Create numbered lists by starting lines with a number and a dot

> Quote text by starting lines with >

Mention another user by @username

For syntax highlighting, surround the code block with three backticks:

```
Your code goes here
```
Just like Github, a blank line must precede a code block.

If you upload more than 5 files we will display all attachments as thumbnails.

For a full reference visit the Markdown syntax.