Dart 2.6 introduces a new language feature called "static extension members".
However, I do not quite understand how to use it.
I would like to easily get the childCount of a Row or Column, i.e. use row.childCount instead of row.children.length:
void main() {
final row = Row(children: const [Text('one'), Text('two')]),
column = Column(children: const [Text('one'), Text('two'), Text('three')]);
print(row.childCount); // Should print "2".
print(column.childCount); // Should print "3".
}
I tried to do the following, but it is a syntax error:
Row.childCount() => this.children.length;
Column.childCount() => this.children.length;
There is an official video by the Flutter team about extension methods now.
Static extension members
Here is an intuitive example of how extension methods work:
extension FancyNum on num {
num plus(num other) => this + other;
num times(num other) => this * other;
}
I simply extend num here and add methods to the class. This could be used like this:
print(5.plus(3)); // Equal to "5 + 3".
print(5.times(8)); // Equal to "5 * 8".
print(2.plus(1).times(3)); // Equal to "(2 + 1) * 3".
Note that the name FancyNum is optional and the following is valid too:
extension on num {}
The extension above will make use of implicit extension member invocations as you do not have to explicitly declare your num to be a FancyNum.
You can also explicitly declare your extension, but this is not needed in most cases:
print(FancyNum(1).plus(2));
Flex childCount
The desired behavior from the question can be achieved by extending Row or Column, or even better: you can extend Flex, which is the super class of Row and Column:
extension ExtendedFlex on Flex {
int get childCount => this.children.length;
}
this. can also be omitted if children is not defined in the current lexical scope of childCount, which means that => children.length is also valid.
With this static extension of Flex imported, you can call it on any Flex, i.e. also on every Row and Column.
Row(children: const [Text('one'), Text('two')]).childCount will evaluate to 2.
Dart 2.7 introduced new Extension Method concept.
https://dart.dev/guides/language/extension-methods
extension ParseNumbers on String {
int parseInt() {
return int.parse(this);
}
double parseDouble() {
return double.parse(this);
}
}
main() {
int i = '42'.parseInt();
print(i);
}
