A slightly revised (last two steps) version of the pseudo-code:
15.5.5.2 [[GetOwnProperty]] (P)
String objects use a variation of the [[GetOwnProperty]] method used for other
native ECMAScript objects (8.6.2.1.2).
Assume S is a String object and P is a string.
When the [[GetOwnProperty]] method of S is called with property name P, the
following steps are taken:
1. Call the default [[GetOwnProperty]] method (8.6.2.1.2) with S as the
this value and argument P.
2. If Result(1) is not undefined return Result(1).
3. If P is not an array index (15.4) , return undefined.
4. Call ToString, giving S as its argument.
5. Call ToInteger(P).
6. Compute the number of characters in Result(4).
7. If Result(5) is less than 0 or is not less than Result(4), return
undefined.
8. Create a string of length 1, containing one character from Result(4),
namely the character at position Result(5), where the first (leftmost)
character in Result(4) is considered to be at position 0, the next one at
position 1, and so on.
9. Return a DDesc with attributes {[[Value]]: Result(8), [[Enumerable]]:
false, [[Writeable]]: false, [[Dynamic]]: false]
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Allen Wirfs-Brock
Sent: Tuesday, June 24, 2008 5:46 PM
To: [EMAIL PROTECTED]; Pratap Lakshman (VJ#SDK)
Cc: [email protected]
Subject: Semantics of "indexed" string access
I've taken a crack at cleaning up Pratap's initial specification for supporting
direct indexing of strings, eg "abc"[1] yields "b"
Here are the semantics that seemed to make sense:
s[n]
1) If s has an own property whose name is the same as the value of n, the
value of that property is returned.
2) else If the value of n is convertible to a number that is within the bounds
of the string value, return a string containing the corresponding character
3) else if try to resolve n as the name of an inherited property
4) else return undefined.
In other words, indexing into a string with a "valid" index returns that
appropriate character unless somebody has explicitly defined a property named
by that index on the object.
If the "index" is not within the bounds of the string it is treated like a
normal property access - If it isn't defined either locally or on the parent
chain the result is undefined.
I've specified this by "over-riding" the definition of [[GetOwnProperty]] for
string instances". Note that literal strings as in the example above will have
been transformed into objects by the property access semantics of 11.2.1
15.5.5.2 [[GetOwnProperty]] (P)
String objects use a variation of the [[GetOwnProperty]] method used for other
native ECMAScript objects (8.6.2.1.2).
Assume S is a String object and P is a string.
When the [[GetOwnProperty]] method of S is called with property name P, the
following steps are taken:
10. Call the default [[GetOwnProperty]] method (8.6.2.1.2) with S as the this
value and argument P.
11. If Result(1) is not undefined return Result(1).
12. If P is not an array index (15.4) , return undefined.
13. Call ToString, giving S as its argument.
14. Call ToInteger(P).
15. Compute the number of characters in Result(4).
16. If Result(5) is less than 0 or is not less than Result(4), return
undefined.
17. Return a string of length 1, containing one character from Result(4),
namely the character at position Result(5), where the first (leftmost)
character in Result(4) is considered to be at position 0, the next one at
position 1, and so on.
Is this a reasonable semantics? Does it match what browsers have already
implemented?
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