Ok, that (cited below) was wrong too.
This should be right:
http://wiki.ecmascript.org/doku.php?id=strawman:default_operator#semantics
Comments welcome. Thanks again, I needed some caffeine!
/be
Brendan Eich wrote:
Heh, I did write *roughly* :-P.
Let lref = evaluate LeftHandSideExpression.
Let lval = GetValue(lref).
Throw a SyntaxError exception if the following conditions are all true:
• Type(lref) is Reference is true
• IsStrictReference(lref) is true
• Type(GetBase(lref)) is Environment Record
• GetReferencedName(lref) is either "eval" or "arguments"
If lval is undefined, then:
Let rref = evaluate AssignmentExpression.
Let rval = GetValue(rref).
Call PutValue(lref, rval).
Thanks, fixing and transcribing into
http://wiki.ecmascript.org/doku.php?id=strawman:default_operator
/be
John Tamplin wrote:
On Tue, Jun 12, 2012 at 3:09 PM, Brendan Eich <[email protected]
<mailto:[email protected]>> wrote:
And (to be clear) the semantics for
LeftHandSideExpression ?= AssignmentExpression
are roughly
Let lref = evaluate A.
Let lval = GetValue(lref).
Let rref = evaluate B.
Let rval = GetValue(rref).
Throw a SyntaxError exception if the following conditions are all
true:
• Type(lref) is Reference is true
• IsStrictReference(lref) is true
• Type(GetBase(lref)) is Environment Record
• GetReferencedName(lref) is either "eval" or "arguments"
If lval is undefined, call PutValue(lref, rval).
to assign the default value if and only if the left-hand side's
current value is undefined.
Wouldn't you want B to be evaluated only if A is undefined?
--
John A. Tamplin
Software Engineer (GWT), Google
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