Optional parameters: Difference between revisions
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(→{{header|Ruby}}: Fill in sort code, showing how to access the hash. Add another example for Ruby 2.0, using MRI 2.0.0dev (2012-01-04 trunk 34211).) |
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=={{header|Ruby}}== |
=={{header|Ruby}}== |
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Ruby does provide a mechanism to specify default values for method arguments: |
Ruby does provide a mechanism to specify default values for method arguments: |
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<lang ruby>def tablesort(table, ordering= |
<lang ruby>def tablesort(table, ordering=proc {|a, b| a <=> b}, column=0, reverse=false) |
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# ...</lang> |
# ...</lang> |
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However, you cannot pass named parameters: if you want to pass "reverse=true", you must also give values for ordering and column. |
However, you cannot pass named parameters: if you want to pass "reverse=true", you must also give values for ordering and column. |
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The idiomatic way in Ruby is to pass a hash or name=>value pairs as method arguments, like this: |
The idiomatic way in Ruby is to pass a hash or name=>value pairs as method arguments, like this: |
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<lang ruby>def |
<lang ruby>def table_sort(table, options = {}) |
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# |
# Provide default values, then merge in caller's options. |
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options = { |
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:ordering => proc {|a, b| a <=> b}, :column => 0, :reverse => false |
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}.merge(options) |
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# |
# Rest of code: |
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column = options[:column] |
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opts.each_pair {|name, value| puts "#{name} => #{value}"} |
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p = options[:ordering].to_proc |
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if options[:reverse] |
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table.sort {|a, b| p.call(b[column], a[column])} |
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else |
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table.sort {|a, b| p.call(a[column], b[column])} |
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end |
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end |
end |
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# Quick example: |
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tablesort(data, "reverse" => true, "column" => 3)</lang> |
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table = [ |
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["Ottowa", "Canada"], |
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["Washington", "USA"], |
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["Mexico City", "Mexico"], |
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] |
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p table_sort(table, :column => 1)</lang> |
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Unknown arguments get ignored. For example, <code>table_sort(table, :typo => 42)</code> just ignores the unknown ''typo'' parameter. |
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Starting with Ruby 1.9, the shortcut syntax <code>column: 1</code> is same as <code>:column => 1</code>. |
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{{works with|Ruby|1.9}} |
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<lang ruby>def table_sort(table, options = {}) |
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# Provide default values, then merge in caller's options. |
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options = { |
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ordering: proc {|a, b| a <=> b}, column: 0, reverse: false |
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}.merge(options) |
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# ... |
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end |
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# ... |
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p table_sort(table, column: 1)</lang> |
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===Ruby's future=== |
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A future version, Ruby 2.0 will have keyword arguments. |
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{{works with|MRI|2.0.0dev (2012-01-04 trunk 34211)}} |
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<lang ruby>def table_sort(table, ordering: :<=>, column: 0, reverse: false) |
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p = ordering.to_proc |
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if reverse |
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table.sort {|a, b| p.(b[column], a[column])} |
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else |
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table.sort {|a, b| p.(a[column], b[column])} |
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end |
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end</lang> |
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Now ''ordering'', ''column'' and ''reverse'' are local variables, not hash keys. Further, this feature also checks for invalid keys. For example, <code>table_sort(table, typo: 42)</code> raises ArgumentError. |
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=={{header|Scala}}== |
=={{header|Scala}}== |
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