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digitalmars.D.learn - UFCS not working with alias

reply Andre Pany <andre s-e-a-p.de> writes:
Hi,

I just noticed ufcs does not work with alias. Is this limitation 
needed?

void foo(int a) {}

void main()
{
	alias bar = foo;
	3.foo();
	3.bar();
}

Last line fails  with "no property 'bar' for type int.

Should I open an enhancement request?

Kind regards
André
Sep 07 2016
parent reply rikki cattermole <rikki cattermole.co.nz> writes:
On 07/09/2016 8:06 PM, Andre Pany wrote:

 Should I open an enhancement request?


No.
It works outside of the function (part of lookup rules).
Sep 07 2016
parent reply Andre Pany <andre s-e-a-p.de> writes:
On Wednesday, 7 September 2016 at 08:08:34 UTC, rikki cattermole 
wrote:

 On 07/09/2016 8:06 PM, Andre Pany wrote:

 Should I open an enhancement request?


 No.
 It works outside of the function (part of lookup rules).


I simplified my example too much. Yes in the example above I can 
move the alias
outside the main function. Here is a more complex example.

As I use the input parameter args in the alias, I cannot move the 
alias outside
the main function.

import std.algorithm;
bool fulfillsKeyPredicate(string s, string t) {return true;}

void main(string[] args)
{
	alias keyPredicateFilter = filter!(e => 
e.fulfillsKeyPredicate(args[0]));
	string[] arr;
	
	keyPredicateFilter(arr);
	arr.keyPredicateFilter;
}

Is there a workaround? Or is still a valid scenario to change the 
lookup rules?

Kind regards
André
Sep 07 2016
next sibling parent reply rikki cattermole <rikki cattermole.co.nz> writes:
On 07/09/2016 8:26 PM, Andre Pany wrote:

 On Wednesday, 7 September 2016 at 08:08:34 UTC, rikki cattermole wrote:

 On 07/09/2016 8:06 PM, Andre Pany wrote:

 Should I open an enhancement request?


 No.
 It works outside of the function (part of lookup rules).


 I simplified my example too much. Yes in the example above I can move
 the alias
 outside the main function. Here is a more complex example.

 As I use the input parameter args in the alias, I cannot move the alias
 outside
 the main function.

 import std.algorithm;
 bool fulfillsKeyPredicate(string s, string t) {return true;}

 void main(string[] args)
 {
     alias keyPredicateFilter = filter!(e =>
 e.fulfillsKeyPredicate(args[0]));
     string[] arr;

     keyPredicateFilter(arr);
     arr.keyPredicateFilter;
 }

 Is there a workaround? Or is still a valid scenario to change the lookup
 rules?


People have tried, this is the behavior as designed.

The workaround is simple, don't use UFCS.

I won't repeat the explanation or reasoning here, plenty of posts on it ;)
Sep 07 2016
parent Andre Pany <andre s-e-a-p.de> writes:
On Wednesday, 7 September 2016 at 08:35:26 UTC, rikki cattermole 
wrote:

 On 07/09/2016 8:26 PM, Andre Pany wrote:

 [...]


 People have tried, this is the behavior as designed.

 The workaround is simple, don't use UFCS.

 I won't repeat the explanation or reasoning here, plenty of 
 posts on it ;)


Thanks, this answer my question.

Kind regards
André
Sep 07 2016
prev sibling parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
On 9/7/16 4:26 AM, Andre Pany wrote:

 On Wednesday, 7 September 2016 at 08:08:34 UTC, rikki cattermole wrote:

 On 07/09/2016 8:06 PM, Andre Pany wrote:

 Should I open an enhancement request?


 No.
 It works outside of the function (part of lookup rules).


 I simplified my example too much. Yes in the example above I can move
 the alias
 outside the main function. Here is a more complex example.

 As I use the input parameter args in the alias, I cannot move the alias
 outside
 the main function.

 import std.algorithm;
 bool fulfillsKeyPredicate(string s, string t) {return true;}

 void main(string[] args)
 {
     alias keyPredicateFilter = filter!(e =>
 e.fulfillsKeyPredicate(args[0]));
     string[] arr;

     keyPredicateFilter(arr);
     arr.keyPredicateFilter;
 }

 Is there a workaround? Or is still a valid scenario to change the lookup
 rules?


There is a workaround, identified by Vladimir Panteleev 
(https://blog.thecybershadow.net/2015/04/28/the-amazing-template-that-does-nothing/):


import std.algorithm;
bool fulfillsKeyPredicate(string s, string t) {return true;}

alias I(alias x) = x;

void main(string[] args)
{
     alias keyPredicateFilter = filter!(e => 
e.fulfillsKeyPredicate(args[0]));
     string[] arr;

     keyPredicateFilter(arr);
     arr.I!keyPredicateFilter;
}

Unfortunately, you can't alias the I!someSymbol, as that has the same 
problem.

-Steve
Sep 08 2016
parent Andre Pany <andre s-e-a-p.de> writes:
On Thursday, 8 September 2016 at 13:38:54 UTC, Steven 
Schveighoffer wrote:

 There is a workaround, identified by Vladimir Panteleev 
 (https://blog.thecybershadow.net/2015/04/28/the-amazing-template-that-does-nothing/):


 import std.algorithm;
 bool fulfillsKeyPredicate(string s, string t) {return true;}

 alias I(alias x) = x;

 void main(string[] args)
 {
     alias keyPredicateFilter = filter!(e => 
 e.fulfillsKeyPredicate(args[0]));
     string[] arr;

     keyPredicateFilter(arr);
     arr.I!keyPredicateFilter;
 }

 Unfortunately, you can't alias the I!someSymbol, as that has 
 the same problem.

 -Steve


Thanks for this insight. In my case I prepare a presentation 
about D
(audience doesn't now anything about D)
and tried to make my D code as beautiful as possible. As solution
I created now a free template method and hide it in a library 
module.

T[] filterByKeyPredicate(T)(T[] arr, string[string] keyPredicate)
{
...filter!....
}

This way I can use UFCS.

Kind regards
André
Sep 08 2016