Use Map with OptionValue

Asked Feb 16 '14 at 23:42

Active Feb 16 '14 at 23:42

Viewed 48 times

Trying to map OptionValue to a list of option names doesn't work.

options = {opt1, opt2, opt3};
Options[f] = # -> True & /@ options;
f[x_, o:OptionsPattern[]] := OptionValue /@ options;
f[x_] := f[x, Sequence@{}];

Executing

f[1, opt1 -> False]

gives the result

{OptionValue[opt1], OptionValue[opt2], OptionValue[opt3]}

instead of the expected

{False, True, True}

Why does this happen with OptionValue and can it be fixed?

asked Feb 16 '14 at 23:42

Tyilo

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25

Use f[x_, o : OptionsPattern[]] := Evaluate[OptionValue /@ options]; instead – Dr. belisarius Feb 16 '14 at 23:53
@belisarius The problem with this is that the r.h.s. will evaluate immediately. – Leonid Shifrin Feb 16 '14 at 23:54
Here is the fix: f[x_, o : OptionsPattern[]] := OptionValue[#] & /@ options;. For an explanation, read this discussion. – Leonid Shifrin Feb 16 '14 at 23:56
In fact, this is an exact duplicate of that one, so I am voting to close... – Leonid Shifrin Feb 16 '14 at 23:57
@rm-rf Well, that was fast ... – Leonid Shifrin Feb 16 '14 at 23:58
@LeonidShifrin I guess we both found the duplicate at the same time :) – rm -rf Feb 16 '14 at 23:58
@LeonidShifrin yeah, Options seem misleadingly simple :) – Dr. belisarius Feb 16 '14 at 23:59
@rm-rf And apparently, commented at the same time too. Fastest gun in the West :) – Leonid Shifrin Feb 16 '14 at 23:59
@belisarius Oh yes :) – Leonid Shifrin Feb 16 '14 at 23:59
@LeonidShifrin I knew exactly what to look for — all I did was search for user:81 "OptionValue" magical as soon as I saw the title :) – rm -rf Feb 17 '14 at 00:00
@rm-rf Me too - I looked for "evaluation of OptionValue" - I remembered the exact name of the question. It took me some time though to realize that that was the exact dupe. – Leonid Shifrin Feb 17 '14 at 00:01
@LeonidShifrin Memoizing question names? – Dr. belisarius Feb 17 '14 at 00:03
@belisarius Been doing that from the start, buddy :) Actually, my memory has some peculiar property that I remember a lot of background details like names of some supporting characters in second-rate movies for which I may not even remember much else. I often wish to clean up lots of garbage that I keep somehow - and the question names are by far not the worst of these things. – Leonid Shifrin Feb 17 '14 at 00:05
@belisarius In fact, remembering my past posts on SE, SO and MathGroup is perhaps a single most constructive use of this property I have, which somehow allows me to live in peace with this. – Leonid Shifrin Feb 17 '14 at 00:07
@LeonidShifrin Try to find a good translation of this story:http://en.wikipedia.org/wiki/Funes_the_Memorious. (the plot summary in Wikipedia is a shame) – Dr. belisarius Feb 17 '14 at 00:18
@belisarius Well, yes, this sounds somewhat similar. Will look for it when I get some time. I've read other things from Borges, but not this one. – Leonid Shifrin Feb 17 '14 at 00:26

Use Map with OptionValue

0 Answers0