Important concepts
Domains:
Dart
As you learn about the Dart language, keep these facts and concepts in mind:
-
Everything you can place in a variable is an object, and every object is an instance of a class. Even numbers, functions, and
null
are objects. All objects inherit from theObject
class. -
Although Dart is strongly typed, type annotations are optional because Dart can infer types. In the code above,
number
is inferred to be of typeint
. When you want to explicitly say that no type is expected, use the special typedynamic
. -
Dart supports generic types, like
List<int>
(a list of integers) orList<dynamic>
(a list of objects of any type). -
Dart supports top-level functions (such as
main()
), as well as functions tied to a class or object (static and instance methods, respectively). You can also create functions within functions (nested or local functions). - Similarly, Dart supports top-level variables, as well as variables tied to a class or object (static and instance variables). Instance variables are sometimes known as fields or properties.
-
Unlike Java, Dart doesn’t have the keywords
public
,protected
, andprivate
. If an identifier starts with an underscore (_
), it’s private to its library. For details, see Libraries and visibility. -
Identifiers can start with a letter or underscore (
_
), followed by any combination of those characters plus digits. -
Dart has both expressions (which have runtime values) and statements (which don’t). For example, the conditional expression
condition ? expr1 : expr2
has a value ofexpr1
orexpr2
. Compare that to an if-else statement, which has no value. A statement often contains one or more expressions, but an expression can’t directly contain a statement. - Dart tools can report two kinds of problems: warnings and errors. Warnings are just indications that your code might not work, but they don’t prevent your program from executing. Errors can be either compile-time or run-time. A compile-time error prevents the code from executing at all; a run-time error results in an exception being raised while the code executes.