On 3/24/13 1:09 AM, Patrick Walton wrote:
I'd like to use the colon for type ascription (i.e. an *assertion*
that a value has some type), which is different from a cast. This
would be useful to help along the typechecker in cases in which it
doesn't have enough information to determine the result of an
expression. For example:
I see that Scala uses the colon for type ascription like you describe,
so you have precedent on your side. :)
http://docs.scala-lang.org/style/types.html#ascription
Similar syntax is OCaml's :> for (static) upcasts and :?> for (dynamic)
downcasts. That's not helpful for casting types that don't have a
subtype relationship, such as u8 and u16 in my example earlier. However,
rust's integral types could be special-cased such that:
let big = 0x54321;
let a = big :> u16; // big & 0xffff truncated like C
let b = big :?> u16; // fail! runtime error because big is out of range
chris
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