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