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Simplification of ES2015 RegExp semantics #89

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Simplification of ES2015 RegExp semantics #89

wants to merge 3 commits into from

Commits on Oct 16, 2015

  1. Specialize RegExp methods to only work on real RegExp instances 

    In ES2015, regular expression methods like RegExp.prototype[Symbol.search]
invoked the receiver's "exec" method to get at the core of matching.
This patch removes that extra degree of genericity to call out to
the builtin RegExp exec implementation directly. Type checks are
added where appropriate to ensure that this direct call is safe.
    @littledan
    littledan committed Oct 16, 2015
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  2. Replace internal use of flag getters with [[OriginalFlags]] 

    In some places in the ES2015 RegExp specification, flag values are
read from [[OriginalFlags]], and in other places, they are read
by invoking Get() on the RegExp to get the flag value.
This inconsistency does not have any obvious benefits for subclassing
and may have some performance cost. This patch standardizes on
reading flag values from [[OriginalFlags]].
    @littledan
    littledan committed Oct 16, 2015
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  3. Factor out a stateless InnerRegExpExec 

    Previously, the ES spec matched RegExps using a RegExpExec internal
algorithm. This algorithm has a couple properties which don't
completely with its usages, leading to awkward workarounds:

- It modifies lastIndex
- There is no mechanism for passing additional flags

Now that "exec" is not called as a method, but rather RegExpExec
is directly invoked from methods like RegExp.prototype[Symbol.split],
it is possible to refactor RegExpExec to create InnerRegExpExec
which does not have these issues.

This patch does that refactoring and takes advantage of it to remove
the lastIndex "save and restore" from RegExp.prototype[Symbol.search]
and, more importantly, the extra RegExp allocation from
RegExp.prototype[Symbol.split]. This is a normative change, since
it affects when the lastIndex property is read and written.
    @littledan
    littledan committed Oct 16, 2015
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