On 1/21/2013 10:57 AM, David Lee wrote:
--
Because "treat as" is an assertion designed so the query author can
tell a pessimistic static type checker to get out of the way and mind
its own business, it is needed only in systems that do pessimistic
static type checking, which are very few and far between. (Galax and
SQL Server are the only ones that come to mind).
Michael Kay
Saxonica
----
Do you know of any cases where "treat as" is necessary in XQuery ?
Or is it the equivalent of a static assert that otherwise would cause
a dynamic error ?
David - I've run across them in a somewhat obscure context, I guess.
I've written an XQuery processor that rewrites queries originally parsed
by Saxon, basically serializing them in the process. All I can tell you
is that Saxon generates an internal expression (ItemChecker) that is
documented as corresponding to "treat as" in some cases where there was
no "treat as" in the original supplied expression.
I think this happens, eg, if you declare a variable with a certain type
(so the type will be checked dynamically when the assignment is done),
but later references to the variable's value can be wrapped in a "treat
as" so that the compiler can assume that the variable has the declared
type and perform suitable automatic type inferencing. But that's just a
guess :)
-Mike
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