Semantics of "indexed" string access

Allen Wirfs-Brock Allen.Wirfs-Brock at
Tue Jun 24 21:34:11 PDT 2008

"abc"[1]   Would presumably parse as:

MemberExpression [ Expression ]

Whose semantic are:
1. Evaluate MemberExpression.
2. Call GetValue(Result(1)).
3. Evaluate Expression.
4. Call GetValue(Result(3)).
5. Call ToObject(Result(2)).
6. Call ToString(Result(4)).
7. Return a value of type Reference whose base object is Result(5) and whose property name is

Note that steps 1,2, and 5 amount to ToObject(GetValue("abc")).  GetValue("abc") yields "abc" so this is really just ToObject("abc").  9.9 says ToObject when applied to a s primitive string: "Create a new String object whose [[value]] property is set to the value of the string.".  That string object becomes the base object of the resulting Reference.  So the literal get converted into an object that  has a [[Get]]
From: Brendan Eich [mailto:brendan at]
Sent: Tuesday, June 24, 2008 7:34 PM
To: Allen Wirfs-Brock; Maciej Stachowiak
Cc: es3.x-discuss at x-discuss; Pratap Lakshman (VJ#SDK); es4-discuss at es4-discuss
Subject: Re: Semantics of "indexed" string access

On Jun 24, 2008, at 6:39 PM, Allen Wirfs-Brock wrote:

Actually, the intent was to support "indexed" access to both string values and string wrapper objects.  I just didn't make it clear in the example.  The case analysis was intended to apply to both. My reading of section 11.2.1 is that  a string value is to be transformed into an object before any actual property access semantics are applied. Am I wrong?

No, the primitive string type (called "String", confusingly, in ES1-3 when it uses type names) is not an object. It has no internal methods such as [[Get]].

Specifying the indexed unit-string access semantic based on the wrapper String (spelled as in the language) object seems ok. I noted a Result(4) that should have been Result(6) in step 7, via private email to Allen (this type of error is going to happen a lot; count on it).

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