Consider the following piece of code:

Options[f] = {Option -> True};
f[x_, OptionsPattern[]] := Module[{option},
     option = OptionValue@Option;
     If[option, x + 1, x]

f[4, {{}, {}}, Option -> True, {}, {}]
f[4, {{}}, {}, {}]


Why does the function f ignore that empty lists and returns the same output as without them instead of returning the same input ? How this behaviour can be avoided ?


1 Answer 1


Why does the function f ignore that empty lists ...

This is because options can be given in a list, so they can easily be stored and passed around.

opts = {PlotRange -> {-2, 2}, PlotStyle -> Red};
Plot[Sin[x] + Sin[1.4 x], {x, 0, 10}, Evaluate[opts]]

From OptionsPattern:

OptionsPattern matches any sequence or nested list of rules, specified with -> or :>.

Thus an empty list will match, and it is equivalent to giving no options.

How this behaviour can be avoided ?

The best answer really depends on why you want to avoid this, so I am going to stop here. This behaviour is generally preferable. It may be inconvenient when you want to allow both options and optional arguments.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.