Gpc March 1997

gpc@gnu.de

17 participants
53 discussions

Re: Protected parameters
by Berend de Boer 08 Mar '97

08 Mar '97

>> Does that mean that protected (not protected var) parameters >> are passed by value? Especially in the case of large >> structures, can this be inefficient, taking up stack space >> and consuming time to copy the arguments? > Yes. :-( >> Or does the standard prescribe something different? > Yes. It requires that the value of the protected formal > parameter cannot change during the execution of the function, The standard doesn't define it this way. I too think that protected should be treated exactly like var parameters, or whatever is as efficient or more efficient (that's why I use const parameters for in Borland Delphi). The standard says this about protected parameters:

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Re: Protected parameters
by Peter Gerwinski 08 Mar '97

08 Mar '97

According to Frank Heckenbach: > Does that mean that protected (not protected var) parameters are passed > by value? Especially in the case of large structures, can this be > inefficient, taking up stack space and consuming time to copy the > arguments? Yes. :-( > Since protected parameters are read-only anyway, actually I see no need > to distinguish between passing them by value or by reference. Of course, > it would be best if the compiler could automatically choose the more > efficient way of passing (i.e. small structures by value, and large ones > by reference), no matter if declared as "protected", "protected var" or > "const". I agree. But ... > Or does the standard prescribe something different? Yes. It requires that the value of the protected formal parameter cannot change during the execution of the function, so things like the following require it to pass everything by value: Var X: Something; Procedure foo ( protected a: Something; Var b: Something ); begin (* foo *) b:= SomeValue; end (* foo *); begin foo ( X, X ); end. (One might ask what purpose `protected' serves when it requires to pass everything by value anyway ... ;-) > Also, defining "Const" as "protected Var" is not completely compatible to BP, > since in BP you can pass a calculated expression, not only an "lvalue" as a > const parameter. I have planned to enable this, too. Then `Const' parameters will indeed be something different than `protected' ones. It could be a good idea to pass small things by value for `Const' parameters ... and relatively easy to implement ... Okay, I am working on it, but ... > But of course, these are no urgent issues, as long as one form of > protected/const parameters works at all... :-) ... with low priority. ;-) Peter Dipl.-Phys. Peter Gerwinski, Essen, Germany, free physicist and programmer peter.gerwinski(a)uni-essen.de - http://home.pages.de/~peter.gerwinski/ [970201] maintainer GNU Pascal - http://home.pages.de/~gnu-pascal/ [970125]

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Re: Protected parameters (Was: Some bug reports - and success report)
by Frank Heckenbach 04 Mar '97

04 Mar '97

Peter Gerwinski wrote: > According to Frank Heckenbach: > > Just wondering - what's the difference between "Const" and "Protected" > > parameters? Are they only handled differently internally in the compiler, > > or is there any semantic difference? > > `Protected' is a "modifier" which can be used with or without `Var' > in formal parameters. `Const' parameters are the same as `protected > Var' parameters Does that mean that protected (not protected var) parameters are passed by value? Especially in the case of large structures, can this be inefficient, taking up stack space and consuming time to copy the arguments? Since protected parameters are read-only anyway, actually I see no need to distinguish between passing them by value or by reference. Of course, it would be best if the compiler could automatically choose the more efficient way of passing (i.e. small structures by value, and large ones by reference), no matter if declared as "protected", "protected var" or "const". Or does the standard prescribe something different? Also, defining "Const" as "protected Var" is not completely compatible to BP, since in BP you can pass a calculated expression, not only an "lvalue" as a const parameter. But of course, these are no urgent issues, as long as one form of protected/const parameters works at all... :-) Frank -- Frank Heckenbach, Erlangen, Germany heckenb(a)mi.uni-erlangen.de Turbo Pascal: http://www.mi.uni-erlangen.de/~heckenb/programs.htm Internet links: http://www.mi.uni-erlangen.de/~heckenb/links.htm

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Gpc March 1997