digitalmars.D - [OT] C# 6.0 ?. null propagation operator

weaselcat (7/7) Apr 20 2015 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_...

Jakob Ovrum (4/11) Apr 20 2015 This is what I came up with for D:

Atila Neves (3/17) Apr 20 2015 Here's mine:

rumbu (9/29) Apr 20 2015 I fail to understand Atila example. Just to be sure:

deadalnix (4/35) Apr 20 2015 These API look overly complex. Why not simply:

rumbu (4/21) Apr 20 2015 Because CurrentUser, GetRole() and Name can also return null in

=?UTF-8?B?QWxpIMOHZWhyZWxp?= (5/29) Apr 20 2015 The solution linked elsewhere in this thread solves that issue as well:
deadalnix (2/26) Apr 20 2015 No, they all return a maybe, that is the nature of maybe monad.

JT (2/5) Apr 20 2015 Where can I find this "maybe" monad implementation?

Atila Neves (5/10) Apr 21 2015 In the Haskell prelude? :P

Atila Neves (9/40) Apr 21 2015 I was trying to write a Maybe monad in D, not make it easy to use.

Vladimir Panteleev (3/17) Apr 20 2015 Mine:

thedeemon (3/6) Apr 20 2015 And we have a winner!

Meta (4/11) Apr 20 2015 HS Teoh came up with a beautiful solution using opDispatch, but I

Daniel N (2/16) Apr 20 2015 http://forum.dlang.org/thread/lnsc0c$1sip$1@digitalmars.com?page=6#post-...

"weaselcat" <weaselcat gmail.com> writes:

http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

of interesting note was the nim sample on how to implement the 
same thing in nim in 2 lines of code

template `?.`(a, b): expr =
   if a != nil: a.b else: nil

template `??`(a, b): expr =
   if a != nil: a else: b

Apr 20 2015

"Jakob Ovrum" <jakobovrum gmail.com> writes:

On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement the 
 same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
   if a != nil: a.b else: nil

 template `??`(a, b): expr =
   if a != nil: a else: b

This is what I came up with for D:

     https://gist.github.com/JakobOvrum/7e3a7bc130ab7db28de3

Meh.

Apr 20 2015

"Atila Neves" <atila.neves gmail.com> writes:

On Monday, 20 April 2015 at 12:16:21 UTC, Jakob Ovrum wrote:
 On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement the 
 same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
  if a != nil: a.b else: nil

 template `??`(a, b): expr =
  if a != nil: a else: b

 This is what I came up with for D:

     https://gist.github.com/JakobOvrum/7e3a7bc130ab7db28de3

 Meh.

Here's mine:

https://gist.github.com/atilaneves/727d63f0a7029032d7ac

Apr 20 2015

"rumbu" <rumbu rumbu.ro> writes:

On Monday, 20 April 2015 at 15:37:02 UTC, Atila Neves wrote:
 On Monday, 20 April 2015 at 12:16:21 UTC, Jakob Ovrum wrote:
 On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement 
 the same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
 if a != nil: a.b else: nil

 template `??`(a, b): expr =
 if a != nil: a else: b

 This is what I came up with for D:

    https://gist.github.com/JakobOvrum/7e3a7bc130ab7db28de3

 Meh.

 Here's mine:

 https://gist.github.com/atilaneves/727d63f0a7029032d7ac


I fail to understand Atila example. Just to be sure:


var roleName = userManager.CurrentUser?.GetRole()?.Name;

D (Jakob):
auto roleName = userManager.getOrNull!("CurrentUser", "GetRole", 
"Name");

D (Atila):
auto roleName = ?

Apr 20 2015

"deadalnix" <deadalnix gmail.com> writes:

On Monday, 20 April 2015 at 20:09:59 UTC, rumbu wrote:
 On Monday, 20 April 2015 at 15:37:02 UTC, Atila Neves wrote:
 On Monday, 20 April 2015 at 12:16:21 UTC, Jakob Ovrum wrote:
 On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement 
 the same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
 if a != nil: a.b else: nil

 template `??`(a, b): expr =
 if a != nil: a else: b

 This is what I came up with for D:

   https://gist.github.com/JakobOvrum/7e3a7bc130ab7db28de3

 Meh.

 Here's mine:

 https://gist.github.com/atilaneves/727d63f0a7029032d7ac


 I fail to understand Atila example. Just to be sure:


 var roleName = userManager.CurrentUser?.GetRole()?.Name;

 D (Jakob):
 auto roleName = userManager.getOrNull!("CurrentUser", 
 "GetRole", "Name");

 D (Atila):
 auto roleName = ?

These API look overly complex. Why not simply:

maybe(userManager).CurrentUser.GetRole().Name ?

Also, CAPITAL LETTER ARE THE BEST !

Apr 20 2015

"rumbu" <rumbu rumbu.ro> writes:

On Monday, 20 April 2015 at 21:22:53 UTC, deadalnix wrote:
 On Monday, 20 April 2015 at 20:09:59 UTC, rumbu wrote:

..
 I fail to understand Atila example. Just to be sure:


 var roleName = userManager.CurrentUser?.GetRole()?.Name;

 D (Jakob):
 auto roleName = userManager.getOrNull!("CurrentUser", 
 "GetRole", "Name");

 D (Atila):
 auto roleName = ?

 These API look overly complex. Why not simply:

 maybe(userManager).CurrentUser.GetRole().Name ?

 Also, CAPITAL LETTER ARE THE BEST !

Because CurrentUser, GetRole() and Name can also return null in 
this scenario.

Apr 20 2015

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 04/20/2015 03:18 PM, rumbu wrote:
 On Monday, 20 April 2015 at 21:22:53 UTC, deadalnix wrote:
 On Monday, 20 April 2015 at 20:09:59 UTC, rumbu wrote:

 ..
 I fail to understand Atila example. Just to be sure:


 var roleName = userManager.CurrentUser?.GetRole()?.Name;

 D (Jakob):
 auto roleName = userManager.getOrNull!("CurrentUser", "GetRole",
 "Name");

 D (Atila):
 auto roleName = ?

 These API look overly complex. Why not simply:

 maybe(userManager).CurrentUser.GetRole().Name ?

 Also, CAPITAL LETTER ARE THE BEST !

 Because CurrentUser, GetRole() and Name can also return null in this
 scenario.

The solution linked elsewhere in this thread solves that issue as well:

 
http://forum.dlang.org/thread/lnsc0c$1sip$1 digitalmars.com?page=6#post-mailman.2584.1403213951.2907.digitalmars-d:40puremagic.com

Ali

Apr 20 2015

"deadalnix" <deadalnix gmail.com> writes:

On Monday, 20 April 2015 at 22:18:31 UTC, rumbu wrote:
 On Monday, 20 April 2015 at 21:22:53 UTC, deadalnix wrote:
 On Monday, 20 April 2015 at 20:09:59 UTC, rumbu wrote:

 ..
 I fail to understand Atila example. Just to be sure:


 var roleName = userManager.CurrentUser?.GetRole()?.Name;

 D (Jakob):
 auto roleName = userManager.getOrNull!("CurrentUser", 
 "GetRole", "Name");

 D (Atila):
 auto roleName = ?

 These API look overly complex. Why not simply:

 maybe(userManager).CurrentUser.GetRole().Name ?

 Also, CAPITAL LETTER ARE THE BEST !

 Because CurrentUser, GetRole() and Name can also return null in 
 this scenario.

No, they all return a maybe, that is the nature of maybe monad.

Apr 20 2015

"JT" <jt jt.com> writes:

On Monday, 20 April 2015 at 21:22:53 UTC, deadalnix wrote:
 ...
 maybe(userManager).CurrentUser.GetRole().Name ?
 ...

Where can I find this "maybe" monad implementation?

Apr 20 2015

"Atila Neves" <atila.neves gmail.com> writes:

On Tuesday, 21 April 2015 at 02:00:49 UTC, JT wrote:
 On Monday, 20 April 2015 at 21:22:53 UTC, deadalnix wrote:
 ...
 maybe(userManager).CurrentUser.GetRole().Name ?
 ...

 Where can I find this "maybe" monad implementation?

In the Haskell prelude? :P

There was a blog post about monads in D I can no longer find. 
Other than that the only other one I know of is the gist I posted.

Atila

Apr 21 2015

"Atila Neves" <atila.neves gmail.com> writes:

On Monday, 20 April 2015 at 20:09:59 UTC, rumbu wrote:
 On Monday, 20 April 2015 at 15:37:02 UTC, Atila Neves wrote:
 On Monday, 20 April 2015 at 12:16:21 UTC, Jakob Ovrum wrote:
 On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement 
 the same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
 if a != nil: a.b else: nil

 template `??`(a, b): expr =
 if a != nil: a else: b

 This is what I came up with for D:

   https://gist.github.com/JakobOvrum/7e3a7bc130ab7db28de3

 Meh.

 Here's mine:

 https://gist.github.com/atilaneves/727d63f0a7029032d7ac


 I fail to understand Atila example. Just to be sure:


 var roleName = userManager.CurrentUser?.GetRole()?.Name;

 D (Jakob):
 auto roleName = userManager.getOrNull!("CurrentUser", 
 "GetRole", "Name");

 D (Atila):
 auto roleName = ?

I was trying to write a Maybe monad in D, not make it easy to use.
An easy to use solution would probably make use of opDispatch. 
But...:

auto roleName = userManager.bind!(a => a.CurrentUser.bind!(b => 
b.GetRole.bind!(c => c.Name);
//roleName's type is Maybe!string.

The only reason monads are readable in Haskell is due to "do" 
syntax sugar.

Apr 21 2015

"Vladimir Panteleev" <vladimir thecybershadow.net> writes:

On Monday, 20 April 2015 at 12:16:21 UTC, Jakob Ovrum wrote:
 On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement the 
 same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
  if a != nil: a.b else: nil

 template `??`(a, b): expr =
  if a != nil: a else: b

 This is what I came up with for D:

     https://gist.github.com/JakobOvrum/7e3a7bc130ab7db28de3

 Meh.

Mine:

http://dump.thecybershadow.net/f8a172455ca239c35146f5dafdc7d1bc/test.d

Apr 20 2015

"thedeemon" <dlang thedeemon.com> writes:

On Tuesday, 21 April 2015 at 03:35:49 UTC, Vladimir Panteleev 
wrote:
 On Monday, 20 April 2015 at 12:16:21 UTC, Jakob Ovrum wrote:
 Mine:

 http://dump.thecybershadow.net/f8a172455ca239c35146f5dafdc7d1bc/test.d

And we have a winner!

Apr 20 2015

"Meta" <jared771 gmail.com> writes:

On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement the 
 same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
   if a != nil: a.b else: nil

 template `??`(a, b): expr =
   if a != nil: a else: b

HS Teoh came up with a beautiful solution using opDispatch, but I 
can't find the thread right now. That also reminds me that I 
meant to make a PR for it and completely forgot.

Apr 20 2015

"Daniel N" <ufo orbiting.us> writes:

On Monday, 20 April 2015 at 14:19:06 UTC, Meta wrote:
 On Monday, 20 April 2015 at 08:24:08 UTC, weaselcat wrote:
 http://www.reddit.com/r/programming/comments/335b1s/the_new_operator_in_c_6/

 of interesting note was the nim sample on how to implement the 
 same thing in nim in 2 lines of code

 template `?.`(a, b): expr =
  if a != nil: a.b else: nil

 template `??`(a, b): expr =
  if a != nil: a else: b

 HS Teoh came up with a beautiful solution using opDispatch, but 
 I can't find the thread right now. That also reminds me that I 
 meant to make a PR for it and completely forgot.

http://forum.dlang.org/thread/lnsc0c$1sip$1 digitalmars.com?page=6#post-mailman.2584.1403213951.2907.digitalmars-d:40puremagic.com

Apr 20 2015

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digitalmars.D - [OT] C# 6.0 ?. null propagation operator