Naming arguments in Wolfram functions?

Question

Sometimes you have functions with very long argument lists:

f[a_, b_, c_, d_, e_] := c

so is there a way to "name" these arguments (order insensitive) so that users can know what they're getting more easily? In pseudo-code:

f[c = "what I'm getting", a = 1, b = 2, d = 0, e = 1]

This is similar to "record syntax" in other programming languages.

Answer 1

Here's an example for how to combine Options, OptionsPattern, and OptionValue:

First, define the available options for f and their default values:

Options[f] = {"TheMainOption" -> 0,
              "SomeOtherOption" -> 7, 
              "TheLetter" -> "A"};

Then, define the function f (here: make a list of all option values, in a particular order that is independent of the order in which the user specifies the options in the function call):

f[OptionsPattern[]] := {OptionValue["TheMainOption"],
                        OptionValue["SomeOtherOption"],
                        OptionValue["TheLetter"]}

Note that by default, OptionsPattern[] looks up the available options and defaults from the associated definition of Options[f].

Tests: the options can be given in any order, and default values are provided in the definition of Options[f]:

f[]
(*    {0, 7, "A"}    *)

f["TheLetter" -> "Z"]
(*    {0, 7, "Z"}    *)

f["TheLetter" -> "N", "SomeOtherOption" -> -2]
(*    {0, -2, "N"}    *)

Remind me what the options and defaults were for f?

Options[f]
(*    {"TheMainOption" -> 0, "SomeOtherOption" -> 7, "TheLetter" -> "A"}    *)