• Mike (13/13) Feb 06 2014 Can someone please clarify for me which of these is the
• Meta (3/16) Feb 06 2014 `alias this : that` was discussed but has never been implemented,
• Tofu Ninja (2/23) Feb 07 2014 Is alias this = that not a thing? If not, why?
• Daniel Kozak (5/30) Feb 07 2014 Because
• Timon Gehr (7/16) Feb 07 2014 Even if we assume for now that this is somehow bad, it is no reason to
• deadalnix (2/19) Feb 07 2014 +1
• Jakob Ovrum (4/21) Feb 07 2014 Reserving `alias this = ...;` allows adding aliasing of
• Timon Gehr (4/7) Feb 07 2014 What a mess that would be. If the consensus is that alias this syntax
• Mike (3/13) Feb 07 2014 Timon, this makes a lot of sense. Would you mind elaborating
• Timon Gehr (34/46) Feb 08 2014 Assuming that the new member here will just be called opThis (but there
• Jakob Ovrum (3/6) Feb 08 2014 One can easily do that with opDispatch for named members, or
• Timon Gehr (2/8) Feb 08 2014 That's wrapping, not forwarding.
• Jakob Ovrum (3/13) Feb 08 2014 Right, perfect forwarding in D is still quite messy (outside of
• Nick Treleaven (14/22) Feb 13 2014 That syntax is indeed confusing if we also had 'alias this : baz'
• Mike (4/9) Feb 07 2014 I'm calling FUD here. It appears the reason it was removed is
• Jesse Phillips (8/21) Feb 07 2014 I'd like for 'alias that this' to go away.
• Mike (3/10) Feb 07 2014 It appears it has been implemented, but not acted upon:

"Mike" <none none.com> writes:

Can someone please clarify for me which of these is the 
"preferred" syntax?

alias that this;
alias this : that;

The documentation here (http://dlang.org/class.html#AliasThis) 
doesn't mention the latter.  I'll do the unrewarding work of 
updating the docs if someone could just please tell me which 
syntax the core language folks prefer.

Thanks.
Mike

For context:
https://github.com/D-Programming-Language/dmd/pull/1413
https://github.com/D-Programming-Language/dmd/pull/1685

"Meta" <jared771 gmail.com> writes:

On Friday, 7 February 2014 at 07:36:57 UTC, Mike wrote:
 Can someone please clarify for me which of these is the 
 "preferred" syntax?

 alias that this;
 alias this : that;

 The documentation here (http://dlang.org/class.html#AliasThis) 
 doesn't mention the latter.  I'll do the unrewarding work of 
 updating the docs if someone could just please tell me which 
 syntax the core language folks prefer.

 Thanks.
 Mike

 For context:
 https://github.com/D-Programming-Language/dmd/pull/1413
 https://github.com/D-Programming-Language/dmd/pull/1685

`alias this : that` was discussed but has never been implemented, 
so currently the only way to do it is `alias that this`.

"Tofu Ninja" <emmons0 purdue.edu> writes:

On Friday, 7 February 2014 at 07:52:22 UTC, Meta wrote:
 On Friday, 7 February 2014 at 07:36:57 UTC, Mike wrote:
 Can someone please clarify for me which of these is the 
 "preferred" syntax?

 alias that this;
 alias this : that;

 The documentation here (http://dlang.org/class.html#AliasThis) 
 doesn't mention the latter.  I'll do the unrewarding work of 
 updating the docs if someone could just please tell me which 
 syntax the core language folks prefer.

 Thanks.
 Mike

 For context:
 https://github.com/D-Programming-Language/dmd/pull/1413
 https://github.com/D-Programming-Language/dmd/pull/1685

 `alias this : that` was discussed but has never been 
 implemented, so currently the only way to do it is `alias that 
 this`.

Is alias this = that not a thing? If not, why?

"Daniel Kozak" <kozzi11 gmail.com> writes:

On Friday, 7 February 2014 at 20:48:37 UTC, Tofu Ninja wrote:
 On Friday, 7 February 2014 at 07:52:22 UTC, Meta wrote:
 On Friday, 7 February 2014 at 07:36:57 UTC, Mike wrote:
 Can someone please clarify for me which of these is the 
 "preferred" syntax?

 alias that this;
 alias this : that;

 The documentation here 
 (http://dlang.org/class.html#AliasThis) doesn't mention the 
 latter.  I'll do the unrewarding work of updating the docs if 
 someone could just please tell me which syntax the core 
 language folks prefer.

 Thanks.
 Mike

 For context:
 https://github.com/D-Programming-Language/dmd/pull/1413
 https://github.com/D-Programming-Language/dmd/pull/1685

 `alias this : that` was discussed but has never been 
 implemented, so currently the only way to do it is `alias that 
 this`.

 Is alias this = that not a thing? If not, why?

Because
alias this = that;
alias this = anotherThat;

is wierd

Timon Gehr <timon.gehr gmx.ch> writes:

On 02/07/2014 10:02 PM, Daniel Kozak wrote:
 On Friday, 7 February 2014 at 20:48:37 UTC, Tofu Ninja wrote:
 On Friday, 7 February 2014 at 07:52:22 UTC, Meta wrote:
 ...

 Is alias this = that not a thing? If not, why?

 Because
 alias this = that;
 alias this = anotherThat;

 is wierd

Even if we assume for now that this is somehow bad, it is no reason to 
have syntax inconsistent with alias.

int baz(int x){ return x; }
double bar(double x){ return x; }

alias foo = bar;
alias foo = baz;

"deadalnix" <deadalnix gmail.com> writes:

On Friday, 7 February 2014 at 21:30:46 UTC, Timon Gehr wrote:
 On 02/07/2014 10:02 PM, Daniel Kozak wrote:
 On Friday, 7 February 2014 at 20:48:37 UTC, Tofu Ninja wrote:
 On Friday, 7 February 2014 at 07:52:22 UTC, Meta wrote:
 ...

 Is alias this = that not a thing? If not, why?

 Because
 alias this = that;
 alias this = anotherThat;

 is wierd

 Even if we assume for now that this is somehow bad, it is no 
 reason to have syntax inconsistent with alias.

 int baz(int x){ return x; }
 double bar(double x){ return x; }

 alias foo = bar;
 alias foo = baz;

+1

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

On Friday, 7 February 2014 at 21:30:46 UTC, Timon Gehr wrote:
 On 02/07/2014 10:02 PM, Daniel Kozak wrote:
 On Friday, 7 February 2014 at 20:48:37 UTC, Tofu Ninja wrote:
 On Friday, 7 February 2014 at 07:52:22 UTC, Meta wrote:
 ...

 Is alias this = that not a thing? If not, why?

 Because
 alias this = that;
 alias this = anotherThat;

 is wierd

 Even if we assume for now that this is somehow bad, it is no 
 reason to have syntax inconsistent with alias.

 int baz(int x){ return x; }
 double bar(double x){ return x; }

 alias foo = bar;
 alias foo = baz;

Reserving `alias this = ...;` allows adding aliasing of 
constructors in the future, assuming it can be meaningfully 
defined.

Timon Gehr <timon.gehr gmx.ch> writes:

On 02/07/2014 11:23 PM, Jakob Ovrum wrote:

 Reserving `alias this = ...;` allows adding aliasing of constructors in
 the future, assuming it can be meaningfully defined.

What a mess that would be. If the consensus is that alias this syntax 
was a mistake then _both_ forms should be removed and the concept should 
be re-introduced as specially named member instead.

"Mike" <none none.com> writes:

On Friday, 7 February 2014 at 22:55:05 UTC, Timon Gehr wrote:
 On 02/07/2014 11:23 PM, Jakob Ovrum wrote:

 Reserving `alias this = ...;` allows adding aliasing of 
 constructors in
 the future, assuming it can be meaningfully defined.

 What a mess that would be. If the consensus is that alias this 
 syntax was a mistake then _both_ forms should be removed and 
 the concept should be re-introduced as specially named member 
 instead.

Timon, this makes a lot of sense.  Would you mind elaborating 
with a simple syntax sample?

Timon Gehr <timon.gehr gmx.ch> writes:

On 02/08/2014 12:46 AM, Mike wrote:
 On Friday, 7 February 2014 at 22:55:05 UTC, Timon Gehr wrote:
 On 02/07/2014 11:23 PM, Jakob Ovrum wrote:

 Reserving `alias this = ...;` allows adding aliasing of constructors in
 the future, assuming it can be meaningfully defined.

 What a mess that would be. If the consensus is that alias this syntax
 was a mistake then _both_ forms should be removed and the concept
 should be re-introduced as specially named member instead.

 Timon, this makes a lot of sense.  Would you mind elaborating with a
 simple syntax sample?

Assuming that the new member here will just be called opThis (but there 
may well be a more descriptive name) and everything else stays the same, 
it's eg:

struct Tuple(T...){
     T expand;
     alias opThis = expand;
}

struct Foo{
     int opThis;
}

struct Bar{
      property double opThis(){ return ...; }
}

The language would then simply consider members named eg. opThis for 
member forwarding and implicit conversion instead of special alias this 
members.

This will enable what I assume is the more natural use case for the syntax:

class C{
     this(int x){ ... }
     ...
}

class D: C{
     alias this = super; // (inherit constructors)
     this(double y){ ... } // (overload with a new constructor)
}

But having both alias this = ...; and alias ... this; with completely 
different semantics would just be an ugly patchwork, and there really is 
no need for special syntax for alias this, especially given that other 
features like it (eg. opDispatch) are implemented by having the language 
recognize specially named members.

Of course, the design of alias this is also not orthogonal.
Eg. one may want to forward members perfectly without enabling implicit 
conversions. (opForward?)

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

On Saturday, 8 February 2014 at 13:43:23 UTC, Timon Gehr wrote:
 Of course, the design of alias this is also not orthogonal.
 Eg. one may want to forward members perfectly without enabling 
 implicit conversions. (opForward?)

One can easily do that with opDispatch for named members, or 
using std.typecons.Proxy for all members.

Timon Gehr <timon.gehr gmx.ch> writes:

On 02/08/2014 02:59 PM, Jakob Ovrum wrote:
 On Saturday, 8 February 2014 at 13:43:23 UTC, Timon Gehr wrote:
 Of course, the design of alias this is also not orthogonal.
 Eg. one may want to forward members perfectly without enabling
 implicit conversions. (opForward?)

 One can easily do that with opDispatch for named members, or using
 std.typecons.Proxy for all members.

That's wrapping, not forwarding.

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

On Saturday, 8 February 2014 at 14:47:27 UTC, Timon Gehr wrote:
 On 02/08/2014 02:59 PM, Jakob Ovrum wrote:
 On Saturday, 8 February 2014 at 13:43:23 UTC, Timon Gehr wrote:
 Of course, the design of alias this is also not orthogonal.
 Eg. one may want to forward members perfectly without enabling
 implicit conversions. (opForward?)

 One can easily do that with opDispatch for named members, or 
 using
 std.typecons.Proxy for all members.

 That's wrapping, not forwarding.

Right, perfect forwarding in D is still quite messy (outside of 
AliasThis).

Nick Treleaven <ntrel-public yahoo.co.uk> writes:

On 08/02/2014 13:43, Timon Gehr wrote:
 class C{
      this(int x){ ... }
      ...
 }

 class D: C{
      alias this = super; // (inherit constructors)
      this(double y){ ... } // (overload with a new constructor)
 }

That syntax is indeed confusing if we also had 'alias this : baz' 
syntax, because it looks quite like you're saying instances of D convert 
automatically to an instance of C, which is implicit OOP anyway and 
makes that statement look redundant.

That is not the suggested syntax that causes the conflict. Forwarding 
constructors would be done like this:

class D: C{
	alias this = super.this;
}

The idea is that 'alias foo = bar' syntax introduces a new symbol called 
'foo'.

For the record, constructor forwarding is just an idea I discussed with 
Kenji, not something that has been accepted necessarily.

"Mike" <none none.com> writes:

On Friday, 7 February 2014 at 21:02:54 UTC, Daniel Kozak wrote:
 Is alias this = that not a thing? If not, why?

 Because
 alias this = that;
 alias this = anotherThat;

 is wierd

I'm calling FUD here.  It appears the reason it was removed is 
because '=' can be used for aliasing superclass constructors.

(https://github.com/D-Programming-Language/dlang.org/pull/200#issuecomment-11711854)

"Jesse Phillips" <Jesse.K.Phillips+D gmail.com> writes:

On Friday, 7 February 2014 at 07:36:57 UTC, Mike wrote:
 Can someone please clarify for me which of these is the 
 "preferred" syntax?

 alias that this;
 alias this : that;

 The documentation here (http://dlang.org/class.html#AliasThis) 
 doesn't mention the latter.  I'll do the unrewarding work of 
 updating the docs if someone could just please tell me which 
 syntax the core language folks prefer.

 Thanks.
 Mike

 For context:
 https://github.com/D-Programming-Language/dmd/pull/1413
 https://github.com/D-Programming-Language/dmd/pull/1685

I'd like for 'alias that this' to go away.

I'm fine with 'alias this = that'

If we must 'alias this : that' or "this implicitly casts to that" 
is also reasonable to me.

Yes 'alias that this' can stay for backwards compatibility.

No 'alias this : that' has not been implemented (that I'm aware 
of).

"Mike" <none none.com> writes:

On Friday, 7 February 2014 at 22:09:21 UTC, Jesse Phillips wrote:
 I'd like for 'alias that this' to go away.

 I'm fine with 'alias this = that'

 If we must 'alias this : that' or "this implicitly casts to 
 that" is also reasonable to me.

 Yes 'alias that this' can stay for backwards compatibility.

 No 'alias this : that' has not been implemented (that I'm aware 
 of).

It appears it has been implemented, but not acted upon:
https://github.com/D-Programming-Language/dmd/pull/1341