On Mar 7, 2009, at 1:53 PM, Allen Wirfs-Brock wrote:
Your understand in your last paragraph is correct.
In general, the term “type” used in the specification is referring
to the categorization of values defined in Section 8. One of those
“types” is “object”. Functions are values of the object type. The
section 5.2 definition of Type(x) is correct but perhaps should be
elaborated upon as: Type(x) is shorthand for “the type of x” where
possible types are those defined in Section 8 (ie, Undefined, Null,
Boolean, String, Number, Object, Reference, List, Completion,
Property Descriptor, Property Identifier, Lexical Environment, and
Environment Record).
Note that there are very few cases where a value might be either one
of the “ECMAScript language types” (the first 6 types in the list
above) or one the “specification types” (the rest of them) so most
often Type(x) predicates in the specification is just choosing from
among the language types.
This explains it perfectly! Thank you.
The actual coding of this test is obviously implementation dependent
and I’m not familiar with your specific implementation so I can’t
say whether or not the functions you showed are correct.
My initial test tries to rule out exactly all of the "ECMAScript
language types" except an Object one - Undefined, Null, Boolean,
String and Number. I think of these types as of "primitives",
therefore `isPrimitive` function name : ) If a value passed to
`Object.keys` is in a subset of these "language types", then my test
should work properly. If, on the other hand, a value is one of the
"specification types" - there will be false positives. From what I
understand, I shouldn't worry about specification types, as none of
them seem to be able to make its way as an argument of `Object.keys`.
Am I correct?
I’ll think about whether or not I can easily clarify this in the
specification. I’ve always found to definition of Type(x) to be
obscure and hard to find.
That could be beneficial for other people having same doubts as I have
had.
Allen
--
Juriy
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