Optional Arguments
One of the more tedious chores in most languages is extracting optional arguments. Dart’s take on the matter is an altogether pleasant built-in syntax.
Let’s say that we want a function named good_day to print a pleasant greeting, with an optional flag to indicate a follow-up message. Calling such a function in Dart looks like the following.
| functional_programming/optional.dart | |
| | good_day("Bob"); |
| | // Good day, Bob. |
| | good_day("Bob", emphatic: true); |
| | // Good day, Bob. |
| | // I said good day! |
In the second call, we supply the optional emphatic: true option to get the extra message. At first glance, this might look like a HashMap. Closer inspection reveals that there are no curly braces around it. This is not a HashMap
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