The subject of casts has come up in various forms now and then, and with
D2 nearing completion (or whatever you'd like to call it) I think it
should be discussed properly.
Basically, we can divide (explicit) casts into two groups: safe and
unsafe. The safe ones include
- checked base-to-derived casting of class references
- checked casts between struct types
- numeric conversions
while the unsafe are things like
- pointer reinterpretation
- casting away constness
- cast(public), cf. dsimcha's recent proposal
There are probably others I have forgotten. It pains me that I can use
the same keyword to do these two things:
double pi = 3.14;
int i = cast(int) pi;
int j = *cast(int*) π
The former is very common and ought to be done using some (library)
function with a specific rounding mode, not with a cast. The spec
doesn't even say how numbers are rounded when cast is used.
The latter is a very unsafe operation, which should of course be allowed
in a language like D, but it should be clearly marked as unsafe.
Instead, I propose the above operations be written like this:
int i = to!int(pi); // The to function already exists in std.conv
int j = cast!int(pi);
I've never liked the syntax of cast expressions in D -- they look like
nothing else in the entire language -- and changing it like this would
make sure no invalid or dangerous casts are left lying around in old
code causing trouble.
What do you think?
-Lars
