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

On Wed, 22 Oct 2008 22:39:10 +0400, bearophile <bearophileHUGS@lycos.com> wrote:

> 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

You can use the following short-cut to avoid double casting:

if (auto foo = cast(Foo)obj) {
    ...
} else if (auto bar = cast(Bar)bar) {
    ...
} else {
    ...
}

On Wednesday, 22 October 2008 at 18:43:15 UTC, Denis Koroskin wrote:
> On Wed, 22 Oct 2008 22:39:10 +0400, bearophile <bearophileHUGS@lycos.com> wrote:
>
>> [...]
>
> You can use the following short-cut to avoid double casting:
>
> if (auto foo = cast(Foo)obj) {
>     ...
> } else if (auto bar = cast(Bar)bar) {
>     ...
> } else {
>     ...
> }

doesn't work with extern(C++) classes see https://forum.dlang.org/post/nolylatfyjktnvweyxlu@forum.dlang.org

On 2/6/18 4:16 PM, timotheecour wrote:
> On Wednesday, 22 October 2008 at 18:43:15 UTC, Denis Koroskin wrote:
>> On Wed, 22 Oct 2008 22:39:10 +0400, bearophile <bearophileHUGS@lycos.com> wrote:
>>
>>> [...]
>>
>> You can use the following short-cut to avoid double casting:
>>
>> if (auto foo = cast(Foo)obj) {
>>     ...
>> } else if (auto bar = cast(Bar)bar) {
>>     ...
>> } else {
>>     ...
>> }
> 
> doesn't work with extern(C++) classes see https://forum.dlang.org/post/nolylatfyjktnvweyxlu@forum.dlang.org

Thimotheecour, I'm not sure how you find these threads. This one is almost 10 years old! Back then, C++ class integration wasn't even a twinkling in Walter's eye ;)

-Steve

On Tuesday, 6 February 2018 at 21:35:11 UTC, Steven Schveighoffer wrote:
> On 2/6/18 4:16 PM, timotheecour wrote:
>> On Wednesday, 22 October 2008 at 18:43:15 UTC, Denis Koroskin wrote:
>>> On Wed, 22 Oct 2008 22:39:10 +0400, bearophile <bearophileHUGS@lycos.com> wrote:
>>>
>>>> [...]
>>>
>>> You can use the following short-cut to avoid double casting:
>>>
>>> if (auto foo = cast(Foo)obj) {
>>>     ...
>>> } else if (auto bar = cast(Bar)bar) {
>>>     ...
>>> } else {
>>>     ...
>>> }
>> 
>> doesn't work with extern(C++) classes see https://forum.dlang.org/post/nolylatfyjktnvweyxlu@forum.dlang.org
>
> Thimotheecour, I'm not sure how you find these threads. This one is almost 10 years old! Back then, C++ class integration wasn't even a twinkling in Walter's eye ;)
>
> -Steve

Lol, I did the same thing once...I think I may have clicked a link on an old thread, and when I went back to the "page view" it must have gone back to the "page view" where the original thread was listed.   I saw an interesting thread an responded and then someone let me know it was 7 years old...I had no idea!!!

On Tuesday, 6 February 2018 at 21:41:14 UTC, Jonathan Marler wrote:
>
> Lol, I did the same thing once...I think I may have clicked a link on an old thread, and when I went back to the "page view" it must have gone back to the "page view" where the original thread was listed.   I saw an interesting thread an responded and then someone let me know it was 7 years old...I had no idea!!!

Link didn't work for me either and didn't realize it until I checked the date. Was able to use the internet wayback machine to get a snap from like 2008.

well even old threads are useful to update when there's new information ; because they show up in search results so good to keep answers up to date (and provide link to newer info)


On Tue, Feb 6, 2018 at 1:44 PM, jmh530 via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> On Tuesday, 6 February 2018 at 21:41:14 UTC, Jonathan Marler wrote:
>>
>>
>> Lol, I did the same thing once...I think I may have clicked a link on an old thread, and when I went back to the "page view" it must have gone back to the "page view" where the original thread was listed.   I saw an interesting thread an responded and then someone let me know it was 7 years old...I had no idea!!!
>
>
> Link didn't work for me either and didn't realize it until I checked the date. Was able to use the internet wayback machine to get a snap from like 2008.