Square brackets [] are used to specify optional, positional parameters in Dart . readFile(String name, [String mode, String charset = ‘utf-8’]) { // … } For such declaration name is always required while mode and charset are optional.
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The definition of a method, constructor, indexer, or delegate can specify its parameters are required or optional . Any call must provide arguments for all required parameters, but can omit arguments for optional parameters.
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2) constructor with Optional parameter keyword is used in the argument to make it optional for the constructor .
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