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Optional parameters: Difference between revisions
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end program UsingTest</lang>
=={{header|F_Sharp|F#}}==
{{trans|Oz}}
F# supports optional parameters for member functions only, not for free-standing functions.
Optional parameters are marked by using a question mark in front of the identifier. Their values are passed as option types, i.e. as <code>Some value</code> or <code>None</code>. The helper function <code>defaultArg</code> can be used to specify default values. In the example below, we use shadowing in order to reuse the identifiers <code>ordering</code>, <code>column</code> and <code>reverse</code>.
<lang fsharp>type Table(rows:string[][]) =
// in-place sorting of rows
member x.Sort(?ordering, ?column, ?reverse) =
let ordering = defaultArg ordering compare
let column = defaultArg column 0
let reverse = defaultArg reverse false
let factor = if reverse then -1 else 1
let comparer (row1:string[]) (row2:string[]) =
factor * ordering row1.[column] row2.[column]
Array.sortInPlaceWith comparer rows
member x.Print() =
for row in rows do printfn "%A" row
// Example usage
let t = new Table([| [|"a"; "b"; "c"|]
[|""; "q"; "z"|]
[|"can"; "z"; "a"|] |])
printfn "Unsorted"; t.Print()
t.Sort()
printfn "Default sort"; t.Print()
t.Sort(column=2)
printfn "Sorted by col. 2"; t.Print()
t.Sort(column=1)
printfn "Sorted by col. 1"; t.Print()
t.Sort(column=1, reverse=true)
printfn "Reverse sorted by col. 1"; t.Print()
t.Sort(ordering=fun s1 s2 -> compare s2.Length s1.Length)
printfn "Sorted by decreasing length"; t.Print()</lang>
=={{header|J}}==
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