The Persistence of Vision Raytracer (POV-Ray).
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Opened by Mike H - 2010-06-09
Last edited by William F Pokorny - 2016-11-28
FS#124 - variable number of parameters in macros
Many programming languages support an indeterminate number of parameters in functions/macros.
JavaScript for instance supports an “arguments” object.
Lua for instance supports the “args” object.
I would like to see that added to POV as well.
Here’s an JavaScript example:
function ArgTest(a, b){
var i, s = "The ArgTest function expected ";
var numargs = arguments.length; //Get number of arguments passed.
var expargs = ArgTest.length; //Get number of arguments expected.
if (expargs < 2)
s += expargs + " argument. ";
else
s += expargs + " arguments. ";
if (numargs < 2)
s += numargs + " was passed.";
else
s += numargs + " were passed.";
s += "\n\n"
for (i =0 ; i < numargs; i++){ //Get argument contents.
s += " Arg " + i + " = " + arguments[i] + "\n";
}
return(s); //Return list of arguments.
}
Monday, 28 November 2016, 12:32 GMT
Reason for closing: Implemented
Additional comments about closing:
Available in 3.7.1 master branch since commit a572730 was Christoph Lipka, Wed Jun 24 15:18:28 2015 +0200, message: Implement mechanisms to allow omission of macro parameters.
Also documented in:
http://wiki.povray.org/content/ Reference:User_Defined_Macros#Optional_P arameters
Macros never allow variable number of argument (but you might get some macro with 1,2,3.... arguments, as long as you define all versions and the macro processor supports them as different). (they all get inspiration from cpp)
Functions with variable number of parameter... use an array instead! (with or w/o the min & max indexes to use)
renamed the task
I think rather than implement support for an indeterminate number of macro parameters, it would be more helpful to allow for optional macro parameters. (It could neatly fit into the existing POV-Ray syntax using the "#if (defined(...))" construct.)
What's the difference between "indeterminate" and "optional"? Also, having to check for each parameter by hand is a lot of tedious extra work. Other languages already have a more streamlined and natural way of doing this.
You are confusing macros with functions. They are expanded in place, which is different from a function.
I'm not confusing macros with functions. You just think I'm confusing macros with functions. I'm asking that macros have the ability to have optional parameters. Nowhere did I mention functions.
The suggestion made by Christoph Lipka seems good and well suited for macros. However, i think it is way to late in the 3.7 release cycle to modify the parser. Changes there tend to produce unwanted side effects that are extremely hard to track down.
"Macros never allow variable number of argument (but you might get some macro with 1,2,3.... arguments, as long as you define all versions and the macro processor supports them as different)."
Manually overloading the macros you mean.