| Re: Preferred way to get multiple returns from a function [message #75012] |
Mon, 14 February 2011 13:42 |
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James[2]
Messages: 44
Registered: November 2009
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Member |
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On Feb 14, 7:03 am, Paul van Delst <paul.vande...@noaa.gov> wrote:
> James wrote:
>> I am writing a function that fits an ellipse to a 2*N array of
>> points. There are three values to return: the center, semi-major
>> axis, and semi-minor axis. This is a simple program, but it brings up
>> a more general question: what is the preferred IDL way to return
>> multiple values from a function?
>
>> Currently, my program returns a structure containing the elements
>> {center, major, minor}. However, a lot of built-in IDL routines take
>> named variable inputs that are set to the appropriate value on output
>> - so instead of something like:
>
>> ellipse_struct = fit_ellipse(points)
>
>> I would have:
>
>> fit_ellipse, points, center, major, minor
>
>> I'm not sure which is better. C programming has taught me to
>> appreciate structures, but I'd like to code in the conventions of the
>> language. Which would you prefer, and why?
>
> Structure.
>
> Why? Because it produces self-documenting code.
>
> Similar to what R.G.Stockwell said,
>
> ellipse.center
>
> doen't require a comment describing what it is. However, a standalone variable
>
> center
>
> probably does. What is it the centre of? An ellipse? Circle? Generic ROI?
>
> "Encapsulation" may be a bit of an OO buzzword, but even for procedural languages with structures it's an easy way to
> make code more readable and simple to maintain. That may not be an issue for a person or two writing code, but in a
> project where there are many people contributing (and in different timezones) it can be extremely helpful.
>
> And since IDL went OO, I think some of the conventional idioms can be tossed - particular those that are purely for
> procedural languages.
>
> FWIW, I'm dealing with the same issue in Fortran. Ever since it went OO with the Fortran2003 standard, I'm writing all
> new code with an OO bent. Makes home-grown "toolboxes" much easier to reuse.
>
> cheers,
>
> paulv
>
> p.s. And always always use Mike Galloy's unit testing framework too:http://mgunit.idldev.com/ :o)
Thanks for the input, everyone. I am glad to see support for a
structure, since that was my original preference. I like structures
and objects - even in an old-school language like IDL, I always find
my programs make more sense if I use them when possible.
The new OO syntax in 8.0 was a big improvement for me; along with the
hash table and list, this update has made IDL considerably more
pleasant.
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| Re: Preferred way to get multiple returns from a function [message #75024 is a reply to message #75012] |
Mon, 14 February 2011 07:03  |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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James wrote:
> I am writing a function that fits an ellipse to a 2*N array of
> points. There are three values to return: the center, semi-major
> axis, and semi-minor axis. This is a simple program, but it brings up
> a more general question: what is the preferred IDL way to return
> multiple values from a function?
>
> Currently, my program returns a structure containing the elements
> {center, major, minor}. However, a lot of built-in IDL routines take
> named variable inputs that are set to the appropriate value on output
> - so instead of something like:
>
> ellipse_struct = fit_ellipse(points)
>
> I would have:
>
> fit_ellipse, points, center, major, minor
>
> I'm not sure which is better. C programming has taught me to
> appreciate structures, but I'd like to code in the conventions of the
> language. Which would you prefer, and why?
Structure.
Why? Because it produces self-documenting code.
Similar to what R.G.Stockwell said,
ellipse.center
doen't require a comment describing what it is. However, a standalone variable
center
probably does. What is it the centre of? An ellipse? Circle? Generic ROI?
"Encapsulation" may be a bit of an OO buzzword, but even for procedural languages with structures it's an easy way to
make code more readable and simple to maintain. That may not be an issue for a person or two writing code, but in a
project where there are many people contributing (and in different timezones) it can be extremely helpful.
And since IDL went OO, I think some of the conventional idioms can be tossed - particular those that are purely for
procedural languages.
FWIW, I'm dealing with the same issue in Fortran. Ever since it went OO with the Fortran2003 standard, I'm writing all
new code with an OO bent. Makes home-grown "toolboxes" much easier to reuse.
cheers,
paulv
p.s. And always always use Mike Galloy's unit testing framework too: http://mgunit.idldev.com/ :o)
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| Re: Preferred way to get multiple returns from a function [message #75033 is a reply to message #75024] |
Fri, 11 February 2011 18:19 |
R.G.Stockwell
Messages: 163
Registered: October 2004
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Senior Member |
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In article
<6a9748b9-2b9e-4401-ab30-e65d354b6c35@y4g2000prh.googlegroups.com>,
James <donjeezy@gmail.com> wrote:
> I am writing a function that fits an ellipse to a 2*N array of
> points. There are three values to return: the center, semi-major
> axis, and semi-minor axis. This is a simple program, but it brings up
> a more general question: what is the preferred IDL way to return
> multiple values from a function?
>
> Currently, my program returns a structure containing the elements
> {center, major, minor}. However, a lot of built-in IDL routines take
> named variable inputs that are set to the appropriate value on output
> - so instead of something like:
>
> ellipse_struct = fit_ellipse(points)
>
> I would have:
>
> fit_ellipse, points, center, major, minor
>
> I'm not sure which is better. C programming has taught me to
> appreciate structures, but I'd like to code in the conventions of the
> language. Which would you prefer, and why?
My personal preference is to return a structure. They tell you what each
element is, and it has a pleasing "input goes in, output comes out" format.
I have always found the procedure call of inputting outputs somewhat
unpleasant. When some variables are in some out out, some are undefined,
some must defined to be within a certain range and a certain variable type,
then the function call does not make obvious what is happening.
ellipse.center for me is more meaningful and more readable than a,b,c
and frankly, just for job security, I would call that function as
fit_ellipse, in_1, in_2, out_a, out_b
no one would ever be able to debug it. :)
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| Re: Preferred way to get multiple returns from a function [message #75034 is a reply to message #75033] |
Fri, 11 February 2011 17:30 |
Kenneth P. Bowman
Messages: 585
Registered: May 2000
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Senior Member |
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In article
<6a9748b9-2b9e-4401-ab30-e65d354b6c35@y4g2000prh.googlegroups.com>,
James <donjeezy@gmail.com> wrote:
> I am writing a function that fits an ellipse to a 2*N array of
> points. There are three values to return: the center, semi-major
> axis, and semi-minor axis. This is a simple program, but it brings up
> a more general question: what is the preferred IDL way to return
> multiple values from a function?
>
> Currently, my program returns a structure containing the elements
> {center, major, minor}. However, a lot of built-in IDL routines take
> named variable inputs that are set to the appropriate value on output
> - so instead of something like:
>
> ellipse_struct = fit_ellipse(points)
>
> I would have:
>
> fit_ellipse, points, center, major, minor
>
> I'm not sure which is better. C programming has taught me to
> appreciate structures, but I'd like to code in the conventions of the
> language. Which would you prefer, and why?
It depends on the situation. Use whichever is more convenient.
Ken Bowman
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