Functions with both optional arguments and options

I have the following codes:

plotContour[func_,xRange_:{-2,2},yRange_:{-2,2},opts___]:=
ContourPlot[Re[func[x+I*y]],{x,xRange[[1]],xRange[[2]]},{y,yRange[[1]],yRange[[2]]}, opts]

opts passes the optioanl arguments like ContourStyle, ImageSize to the built-in ContourPlot function. I have provided default argument values to xRange and yRange.

But now if I run the following:

plotContour[func,ContourStyle->Red]

I run into problems because it treats ContourStyle->Red as the arguments xRange, so I receive errors (Limiting value ContourStyle in ... is not a machine-sized real number.)

How should I modify the codes so that it works when I provide optional arguments but skip the arguments with default values?

Answer

As already said in a comment, I would not treat what feels more like an option as an usual argument to the function. Instead you can use OptionsPattern and friends.

For a generic function with both own arguments, and potential arguments supplied to functions used within you can use the following design pattern

Define your own function's options in one of the following fashions

1. 
   

   with (protected) symbol (offers the advantage of auto-completion)

   
   

   Protect[xRange, yRange];
   Options[myContourPlot] = {xRange -> {-2, 2}, yRange -> {-2, 2}}
   



2. 
   

   with Strings

   
   

   Options[myContourPlot] = {"xRange" -> {-2, 2}, "yRange" -> {-2, 2}}
   
   

And define your function with

myContourPlot[func_, opts : OptionsPattern[{myContourPlot, ContourPlot}]] := 
Module[{x1, x2, y1, y2},
(* read in your options *)
{x1, x2} = OptionValue[xRange] ;
{y1, y2} = OptionValue[yRange];

ContourPlot[Re[func[x + I*y]], {x, x1, x2}, {y, y1, y2}, 

Evaluate@FilterRules[{opts}, Options@ContourPlot]]]

Now you can call your function with

myContourPlot[Exp, xRange -> {-3, 3}, ContourStyle -> Dashed]

or (depending on your choice concerning symbols or strings as option names)

myContourPlot[Exp, "xRange" -> {-3, 3}, ContourStyle -> Dashed]