i was trying to make a D template to mimic auto-implemented
properties in c#.

I think i got it to work but when i tried to give the template a
more meaning full name like AutoImplementedProperty i get a
compile error "a.title is not an lvalue".
Is this a bug?
Is there a more suitable way of doing this?

c# e.g:
class Bar
{
	public string Title { get; set; }
}

my attempt:
class Bar
{
	alias autoproperty!(string, "get", "set") title
}

template autoproperty(T, args...)
{
	import std.typetuple;
	@property
	{		
		private T _name;
		static if (args.length)
		{
			static if (staticIndexOf!("get", args) > -1)
			{
				public T autoproperty()
				{
					return _name;
				}			
			}
	
			static if (staticIndexOf!("set", args) > -1)
			{
				public void autoproperty(T value)
				{
					_name = value;
				}
			}
			
		}
	}
}

void main(string[] args)
{
	Bar a = new Bar();
	a.title = "asf";	
	writefln(a.title);

	return;
}

Hi Michael,

your code works for me (DMD 2.061, Linux), with a semicolon after the alias
in class Bar.

Also, use writeln, not writefln, because writefln assumes the first parameter is the formatting string.

On Saturday, 5 January 2013 at 22:53:44 UTC, Philippe Sigaud wrote:
> Hi Michael,
>
> your code works for me (DMD 2.061, Linux), with a semicolon after the alias
> in class Bar.
>
> Also, use writeln, not writefln, because writefln assumes the first
> parameter is the formatting string.

Why would you want get/set though when D offers property functions?

The argument of "if your public attribute becomes private, then code breaks" is invalid in D.

On Saturday, 5 January 2013 at 22:53:44 UTC, Philippe Sigaud wrote:
> Hi Michael,
>
> your code works for me (DMD 2.061, Linux), with a semicolon after the alias
> in class Bar.
>
> Also, use writeln, not writefln, because writefln assumes the first
> parameter is the formatting string.

Thanks for the tip.
Does it work for you if you rename the template to "AutoImplementedProperty"?

On Saturday, 5 January 2013 at 23:00:48 UTC, monarch_dodra wrote:
> On Saturday, 5 January 2013 at 22:53:44 UTC, Philippe Sigaud wrote:
>> Hi Michael,
>>
>> your code works for me (DMD 2.061, Linux), with a semicolon after the alias
>> in class Bar.
>>
>> Also, use writeln, not writefln, because writefln assumes the first
>> parameter is the formatting string.
>
> Why would you want get/set though when D offers property functions?
>
> The argument of "if your public attribute becomes private, then code breaks" is invalid in D.

I'm not sure if i ever would use the template, but anyway I was having a cs vs d argument with a friend, and we ended up writing code samples for comparison.

This is just one of the items that came up.

On 01/05/2013 03:25 PM, michaelc37 wrote:
> On Saturday, 5 January 2013 at 22:53:44 UTC, Philippe Sigaud wrote:
>> Hi Michael,
>>
>> your code works for me (DMD 2.061, Linux), with a semicolon after the
>> alias
>> in class Bar.
>>
>> Also, use writeln, not writefln, because writefln assumes the first
>> parameter is the formatting string.
>
> Thanks for the tip.
> Does it work for you if you rename the template to
> "AutoImplementedProperty"?

I confirm this: Any name other than the seemingly magical autoproperty causes the following errors:

  Error: a.title is not an lvalue
  Error: expression has no value

Ali

On 01/05/2013 04:32 PM, Ali Çehreli wrote:

> I confirm this: Any name other than the seemingly magical autoproperty
> causes the following errors:
>
> Error: a.title is not an lvalue
> Error: expression has no value

I retract that! :) That happens when I replace only the two "autoproperty" with "AutoImplementedProperty." There is no error when I replace all four! :)

Ali

On 2013-01-05 23:40, michaelc37 wrote:
> i was trying to make a D template to mimic auto-implemented
> properties in c#.
>
> I think i got it to work but when i tried to give the template a
> more meaning full name like AutoImplementedProperty i get a
> compile error "a.title is not an lvalue".
> Is this a bug?
> Is there a more suitable way of doing this?
>
> c# e.g:
> class Bar
> {
>      public string Title { get; set; }
> }
>
> my attempt:
> class Bar
> {
>      alias autoproperty!(string, "get", "set") title
> }
>
> template autoproperty(T, args...)
> {
>      import std.typetuple;
>      @property
>      {
>          private T _name;
>          static if (args.length)
>          {
>              static if (staticIndexOf!("get", args) > -1)
>              {
>                  public T autoproperty()
>                  {
>                      return _name;
>                  }
>              }
>
>              static if (staticIndexOf!("set", args) > -1)
>              {
>                  public void autoproperty(T value)
>                  {
>                      _name = value;
>                  }
>              }
>
>          }
>      }
> }
>
> void main(string[] args)
> {
>      Bar a = new Bar();
>      a.title = "asf";
>      writefln(a.title);
>
>      return;
> }

This won't work like you think it will. All instances of "Bar" will share the same "_name" variable.

You need to use a mixin. This pass:

void main ()
{
    Bar a = new Bar();
    a.title = "asf";

    Bar b = new Bar;
    assert(b.title == a.title);
}


-- 
/Jacob Carlborg

On Sunday, 6 January 2013 at 11:32:40 UTC, Jacob Carlborg wrote:
> On 2013-01-05 23:40, michaelc37 wrote:
>> i was trying to make a D template to mimic auto-implemented
>> properties in c#.
>>
>> I think i got it to work but when i tried to give the template a
>> more meaning full name like AutoImplementedProperty i get a
>> compile error "a.title is not an lvalue".
>> Is this a bug?
>> Is there a more suitable way of doing this?
>>
>> c# e.g:
>> class Bar
>> {
>>     public string Title { get; set; }
>> }
>>
>> my attempt:
>> class Bar
>> {
>>     alias autoproperty!(string, "get", "set") title
>> }
>>
>> template autoproperty(T, args...)
>> {
>>     import std.typetuple;
>>     @property
>>     {
>>         private T _name;
>>         static if (args.length)
>>         {
>>             static if (staticIndexOf!("get", args) > -1)
>>             {
>>                 public T autoproperty()
>>                 {
>>                     return _name;
>>                 }
>>             }
>>
>>             static if (staticIndexOf!("set", args) > -1)
>>             {
>>                 public void autoproperty(T value)
>>                 {
>>                     _name = value;
>>                 }
>>             }
>>
>>         }
>>     }
>> }
>>
>> void main(string[] args)
>> {
>>     Bar a = new Bar();
>>     a.title = "asf";
>>     writefln(a.title);
>>
>>     return;
>> }
>
> This won't work like you think it will. All instances of "Bar" will share the same "_name" variable.
>
> You need to use a mixin. This pass:
>
> void main ()
> {
>     Bar a = new Bar();
>     a.title = "asf";
>
>     Bar b = new Bar;
>     assert(b.title == a.title);
> }

Yea i realized that later, but the only fix i could come up with required me passing the property name in the template parameters, so the declaration has changed a bit.

second attempt;

class Bar
{
	public mixin autoproperty!(string, "title", "get", "set");
	public mixin autoproperty!(string, "description", "get", "set");
}

mixin template autoproperty(T, alias propertyName, args...)
{
	import std.typetuple;

	mixin("private T _" ~ propertyName ~ ";");
		
	@property
	{		
		static if (args.length)
		{
			static if (staticIndexOf!("get", args) > -1)
			{
				mixin("
				T " ~ propertyName ~ "()
				{
					return _" ~ propertyName ~ ";					
				}");
			}
	
			static if (staticIndexOf!("set", args) > -1)
			{
				mixin("
				void " ~ propertyName ~ "(T value)
				{
					_" ~ propertyName ~ " = value;
				}");
			}			
		}
	}	
}