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<<= and << [message #7182]

Sun, 17 December 2006 23:12

Balage
Messages: 17
Registered: December 2006

Promising Member

What's the difference between:

somebutton << THISBACK(Press);

and

somebutton <<= THISBACK(Press);

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Re: <<= and << [message #7183 is a reply to message #7182]

Sun, 17 December 2006 23:48

mirek
Messages: 14255
Registered: November 2005

Ultimate Member

<<= sets the WhenAction callback

<< adds a new callback to existing one; if there were any callbacks before assigned, they will be called as well.

In fact, "<<" is sort of experiment and is very rarely used.

Note: You cannot use somebutton << THISBAC... because "<<" is method of Callback, not Ctrl. You would have to write

somebutton.WhenAction << THISBACK....

Mirek

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Re: <<= and << [message #7184 is a reply to message #7183]

Sun, 17 December 2006 23:57

Balage
Messages: 17
Registered: December 2006

Promising Member

I was just curious, as both worked fine, and produced the same result, I just didn't know what was the diff.

Actually, somebutton << THISBACK(Press) does work!

class Ctrl has these operators:

	Callback     operator<<=(Callback action)  { WhenAction = action; return action; }
	Callback&    operator<<(Callback action)   { return WhenAction << action; }

I tried this:

somebutton << THISBACK(Press) << THISBACK(Press2) << THISBACK(Press3) << THISBACK(Press);

The handlers were called in this order:
Press, Press2, Press3, Press

So with <<, I can add multiple callbacks. That's nice.

[Updated on: Mon, 18 December 2006 00:01]

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Re: <<= and << [message #7187 is a reply to message #7184]

Mon, 18 December 2006 00:16

mirek
Messages: 14255
Registered: November 2005

Ultimate Member

Yes, you are right.

Mirek

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Re: <<= and << [message #12957 is a reply to message #7187]

Fri, 30 November 2007 13:13

waxblood
Messages: 95
Registered: January 2007

Member

Quote:

Reading code snippets in documentation '<<=' is always used instead of <<, but isn't the '<<' behaviour much more natural than the first one? Writing code with '<<' allows the programmer to modify callbacks stack of ancestor classes freely being at least a little more confident that those callbacks will always be executed before any one other callbacks in derived classes.
Using always '<<=' precludes this possibility.

I think it would be useful to develop plugin-oriented programs, too.

I'm wondering, given the fact quite nobody uses the '<<' form, would it be possible to convert the '<<=' behaviour to '<<'?

David

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Re: <<= and << [message #12958 is a reply to message #12957]

Fri, 30 November 2007 13:52

mirek
Messages: 14255
Registered: November 2005

Ultimate Member

waxblood wrote on Fri, 30 November 2007 07:13

Quote:

Interesting thoughts, yes, something like this is definitely possible path.

I guess using "<<=" is a result of two issues:

1. "<<=" existed long before "<<"
2. In real world applications, single action per callback is simply 99% of cases.

Quote:

I'm wondering, given the fact quite nobody uses the '<<' form, would it be possible to convert the '<<=' behaviour to '<<'?

Well, once again interesting idea... But here I am a bit afraid about changed semantics.

Mirek

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Re: <<= and << [message #13046 is a reply to message #12958]

Thu, 06 December 2007 23:44

waxblood
Messages: 95
Registered: January 2007

Member

Quote:

I'm wondering, given the fact quite nobody uses the '<<' form, would it be possible to convert the '<<=' behaviour to '<<'?

Well, once again interesting idea... But here I am a bit afraid about changed semantics.

Mirek

Well, in fact that wasn't a great idea. Here's some better thought:

Quote:

2. In real world applications, single action per callback is simply 99% of cases.

I had the suspect of a similar percentage, but now that it is confirmed I think it's time to plan a switch to the '<<' form. I think these should be the steps to follow:

a) fix the following problem:
writing

somebutton << THISBACK(Press) <<= THISBACK(Press2);

results in a compiling problem, which is right since adding callback Press to just replace it with Press2 with the <<= doesn't make sense. But, if you write

somebutton <<= THISBACK(Press) << THISBACK(Press2);

IMO the compiler shoudn't complain, since replacing callbacks stack with Press and adding then Press2 seems a logic step. In fact the compiler doesn't complain, but at runtime you get no results when pressing somebutton. If this is not a bug, is a bad incongruence at least.

b) start to write new Ultimate++ code with '<<' form.

c) change examples,reference and tutorials (I think this step should be possibly made in one single pass, to avoid generating confusion among users should be just a matter of find & replace (probably replace _all_)

d) place a warning or a suggestion when encountering '<<=', saying in 99% '<<' should be preferred (maybe pointing to an html page explaining way). This should be only a transitional message. Would it be possible to easily turn off the message for upp source?

e) Replace '<<=' in existing code with '<<' (more time consuming).

David

[Updated on: Thu, 06 December 2007 23:52]

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Re: <<= and << [message #13049 is a reply to message #13046]

Fri, 07 December 2007 09:25

mirek
Messages: 14255
Registered: November 2005

Ultimate Member

waxblood wrote on Thu, 06 December 2007 17:44

Quote:

2. In real world applications, single action per callback is simply 99% of cases.

I had the suspect of a similar percentage, but now that it is confirmed I think it's time to plan a switch to the '<<' form.

IMO, you misunderstood me. In 99% cases <<= is OK. Admitedly, in 99% cases of these cases, "<<" is OK as well Smile

Quote:

d) place a warning or a suggestion when encountering '<<=', saying in 99% '<<' should be preferred (maybe pointing to an html page explaining way). This should be only a transitional message. Would it be possible to easily turn off the message for upp source?

IMO, there are about 0.01% of important cases, where "<<=" over "<<" semantics is required...

Mirek

[Updated on: Fri, 07 December 2007 09:25]

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Re: <<= and << [message #13052 is a reply to message #13049]

Fri, 07 December 2007 10:12

waxblood
Messages: 95
Registered: January 2007

Member

luzr wrote on Fri, 07 December 2007 09:25

IMO, you misunderstood me. In 99% cases <<= is OK. Admitedly, in 99% cases of these cases, "<<" is OK as well Smile

For standard apps, '<<=' I'm positive works fine, I just think some problem may arise with general purpose widgets, or 'components'. These should be extensible by nature, and '<<=' doesn't favour extensibility. Having a dynamical feature like callbacks mechanism and preventing to fully exploit it seems like a waste, especially talking about open source software, where you primary rely on re-using classes written by others. If I'd want to write plugin-expandable software (which is quite diffuse nowadays), I think I'd like more '<<' around...

David

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