Options

Options(symbol)

gives a list of optional arguments to symbol and their default values.

You can assign values to ‘Options’ to specify options.

>> Options(f) = {n -> 2}
{n->2}

>> Options(f)
{n->2}

>> f(x_, OptionsPattern(f)) := x ^ OptionValue(n)

>> f(x)
x^2

>> f(x, n -> 3)
x^3

Delayed option rules are evaluated just when the corresponding ‘OptionValue’ is called:

>> f[a :> Print["value"]] /. f[OptionsPattern[{}]] :> (OptionValue[a]; Print["between"]; OptionValue[a]);
 value
 between
 value

In contrast to that, normal option rules are evaluated immediately:

>> f[a -> Print["value"]] /. f[OptionsPattern[{}]] :> (OptionValue[a]; Print["between"]; OptionValue[a]);
 value
 between

Options must be rules or delayed rules:

>> Options[f] = {a}
 {a} is not a valid list of option rules.
{a}

A single rule need not be given inside a list:

>> Options[f] = a -> b
a -> b

>> Options[f]
{a :> b}

Options can only be assigned to symbols:

>> Options[a + b] = {a -> b}
 Argument a + b at position 1 is expected to be a symbol.
{a -> b}