How to create an empty Map in Dart
You can create an empty Map
by using a map literal:
{}
However, if the type is not already known, it will default to Map<dynamic, dynamic>
, which defeats type safety. In order to specify the type for a local variable, you can do this:
final myMap = <String, int>{};
And for non-local variables, you can use the type annotation form:
Map<String, int> myMap = {};
Notes:
Here's how I remember the syntax:
{}
is a literal, and ()
performs an invocation1. T{}
is illegal syntax, and T()
invokes the unnamed constructor for T
. It doesn't matter what T
is, whether it's Map<K, V>
or String
or any other class.
{}
is a literal, but what kind of literal? Is it a Set
or a Map
? To distinguish between them, you should express the type. The way to express types for generics is put types in angle brackets: <K, V>{}
for a Map<K, V>
, and <E>{}
for a Set<E>
.
The same goes for List
s: []
is a literal, and you can specify the type with angle brackets: <E>[]
.
1 Obviously there are many other uses for {}
and ()
in other contexts.