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From |
Sergiy Radyakin <serjradyakin@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: rclass AND sclass AND eclass |

Date |
Tue, 29 Nov 2011 19:25:20 -0500 |

Dear All, the documentation for Stata declares that each program can be either rclass, or sclass, or eclass (or nclass). See -help program-. In many cases this is indeed true, but as the programs become ever more complicated, this strict correspondence breaks down at some level. Here is a trivial demonstration: program foobar foo bar end program foo, rclass return local result = 1 end program bar, sclass sreturn local result = 2 end Here -foobar- is declared as nclass, and its subroutines are declared as rclass and sclass. A casual observer might inspect only the -foobar- main routine, and come to the conclusion that the r- and s-results are safe and not damaged by the command. While in fact the program makes use of both r-results and s-results, and hence this must be clearly documented. Furthermore, as the calls to subroutines may be contingent on some run-time conditions, the r-results/s-results may be destroyed "only sometimes", which makes it hell of a job to debug the program (especially if you are absolutely confident that -foobar- is an nclass program :) The example above is motivated by the real and not too farfetched standard Stata command -mean-, which saves some of the [undocumented] results into r-results, but only in verbose mode (does not save in the quiet mode). Hence two consequences: 1) any program relying on the r-results of mean will [not knowingly] change its behavior depending on whether it is being executed quietly or noisily; 2) any program relying on r-results being intact after -mean- is up for a surprise. More generally, think of turning your recent do file into an ado file. You have probably used dozens of commands each of them affecting r-results or e-results. How would you title your program - rclass? eclass? sclass? Would it make more sense to talk about r-safe (e-safe, s-safe) commands, in the sense that under no conditions the command will affect the results saved in the corresponding area? Alternatively, I see no reason to have rclass, eclass, and sclass as mutually exclusive. They are each exclusive with nclass by definition, but not with each other, as I may want to set both r-results and e-results in the same program. And since I can currently do this in the manner illustrated above by introducing technical subroutines of the proper class, there is no reason to prohibit a command to set the results of multiple types simultaneously. Finally, while we generally learn that estimation commands return their results in e-results, general commands in r-results, and rare commands return results in s-results, IMHO the documentation would benefit if the class of the command is spelled clearly right with the syntax, so that we do not have to scout to "... saves the following in ...". Should we be optimists and interpret the "...saves in r()" as "...saves in r() and leaves e() intact"? or be pessimists and interpret it as "saves in r() and clears e()"? or most inconveniently "...saves in r() and may sometimes clear e()"? I would appreciate if the gurus and novices shared their thoughts on the above questions. Thank you very much, Sergiy Radyakin. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: rclass AND sclass AND eclass***From:*Maarten Buis <maartenlbuis@gmail.com>

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