RegExp free-spacing & comments

[Gorkem Yakin]

I don’t know about other engines, but Chakra does cache the RegExp matcher when the RegExp object is created via the constructor.

Gorkem

From: es-discuss [mailto:es-discuss-bounces at mozilla.org] On Behalf Of Isiah Meadows
Sent: Friday, November 6, 2015 4:36 PM
To: C. Scott Ananian <ecmascript at cscott.net>; Brian Terlson <Brian.Terlson at microsoft.com>
Cc: es-discuss at mozilla.org
Subject: Re: RegExp free-spacing & comments


The problem with using the RegExp constructor is that it is never cached by the engine. As a literal, engines usually internalize them, speeding up matches very quickly.

On Fri, Nov 6, 2015, 14:24 C. Scott Ananian <ecmascript at cscott.net<mailto:ecmascript at cscott.net>> wrote:
On Fri, Nov 6, 2015 at 1:20 PM, Brian Terlson
<Brian.Terlson at microsoft.com<mailto:Brian.Terlson at microsoft.com>> wrote:
> RegExp.re or similar seems nice:
>
> ```
> let re = RegExp.re("x")`
>     (\d{3}-)? # area code (optional)
>     \d{3}-    # prefix
>     \d{4}     # line number
> `;
> ```
>
> But it seems like previous proposals of this want escaping which doesn't seem ideal for this purpose. Do we need both `RegExp.re` and `RegExp.escapedRe`?

Escaping happens if you use interpolation into the string template:
```
let re = RegExp.re`(?x:
    (\d{3}-)?      # area code (optional)
    ${ /\d{3}/ }-  # prefix
    \d{4}           # line number
    ( ${ "*" } \d+ )?  # extension
)`;
```
If the interpolated expression is a regexp, then things seem
relatively straightforward (although there are corner cases to
consider).  If the interpolated expression is a string, then it is
suggested that you use some sort of automatic escaping.
 --scott
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