Craig Ringer wrote:
On 25/09/2010 11:51 AM, Darren Duncan wrote:
There should just be a single syntax that works for all types, in the
general case, for testing whether a value is a member of that type, or
alternately whether a value can be cast to a particular type.
<snip>
Pg already gets it right in this regard by having a single general
syntax for type casting, the "<value>::<type-name>" and value membership
of a type should be likewise.
or the standard:
CAST(value AS typename)
Indeed. The exact syntax doesn't matter to me but the point is that the type
name is its own lexical element, conceptually a function argument, rather than
being a substring of another one.
Maybe to test if a value can be cast as a type, you can continue the ::
mnemonic, say adding a "?" for yes and a "!" for no.
For example, "<value>?::<type-name>" tests if the value can be cast as
the type and "<value>!::<type-name>" or "not <value>?::<type-name>"
tests the opposite. An expression like this results in a boolean.
Personal opinion here: Blech, if I wanted to use Perl6 I'd do so ;-)
I see that someone has been paying attention.
Yes, the idea of using ? or ! to derive a boolean expression from some other
expression did indeed come from Perl 6. The ? means "is so", ! means "is not".
A very useful mnemonic in general.
Good shorthand, I guess, but a CAST syntax extension or alternate CAST
version would be a bonus for readability.
Well, sure. But something consistent with cast syntax that Pg provides.
-- Darren Duncan
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