Casts

[bearophile]

With reddit I have found a page that shows casts in C#:
http://rusek.org/stefan/default.aspx/2008/10/22/the-3-cast-operators-in-c/73/

The default cast of C# throws an exception if the dynamic cast can't be done. Do you see this as safer than the current D1 cast?

The "as" of C# is similar to the current dynamic cast of D1.

The "is" operatotor of C# can be implemented with a cast plus test:
if (cast(Foo)o !is null) { ...
That sometimes I write:
if (IsInstance!(Foo)(o)) { ...

This syntax of C#
something = o as Foo ?? new Foo(0);

Becomes in D:
something = cast(Foo)o;
if (something is null) something = new Foo(0);

Because this shorter code requires two casts, it's slower:
something = cast(Foo)o is null ? new Foo(0) : cast(Foo)o;

I think in D may be useful to split the current cast() into two different syntaxes, one similar the current dynamc cast, and the other that performs a non-aliasing re-interepretation of the given bitpattern (the kind of conversion unions are often used for in C). I find those two cases quite different, but I confuse them in the current D1, so I think they may deserve two different syntaxes. 

(This may look like an increase of the complexity of D, but when two (or more) usages are conflated into a single syntax (or one common usage doesn't have a hansy syntax) then the complexity of the language seems actually higher).

--------------

Sometimes you need to test a given object to many classes:

if (cast(Foo1)obj !is null) {
    ...
} else if (cast(Foo2)obj !is null) {
    ...
} else if (cast(Foo3)obj !is null) {
    ...
} else if (cast(Foo4)obj !is null) {
    ...
} else {
    ...
}

If such idioms are used often enough (in my code I don't use them often) then something shorter and/or faster may be adopted.

Bye,
bearophile