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Description
Named argument
As opposed to named parameters, named arguments is about using the parameter name on the call site.
Named arguments enable you to specify an argument for a positional parameter by matching the argument with its name rather than with its position in the parameter list.
Example:
void main() {
final a = A(x: 1, y: 2);
final another = A(y: 2, x:1);
}
class A {
final int x;
final int y;
A(this.x, this.y);
}Rationale:
The decision to use named or positional arguments can be a decision the call site should make.
Private properties
void main() {
final a = A(x: 1, y: 2);
}
class A {
final int _x;
final int _y;
A(this._x, this._y);
}This could lead to other beneficial features down the line like:
Declaring all fields in a constructor
class A {
final int x;
final int y;
final int z;
A(this.*);
}Related: Object spread shorthand
Syntax sugar ...Object is used in a constructor / function call to unpack labels:
void main() {
final a = A(x: 1, y: 2);
final b = B(...a, z: 3);
// equivalent to
final bWithoutSugar = B(x: a.x, y: a.y, z: 3);
}
class A {
final int x;
final int y;
A(this.x, this.y);
}
class B {
final int x;
final int y;
final int z;
A(this.x, this.y, this.z);...Object unpack the labels with the intersection between the parameters name and the object getters name.
Copies with null values
The last declaration of the field wins, allowing copying with null values (when the fields are not private).
void main() {
final a = A(x: 1, y: 2);
final another = A(...a, y: null);
}
class A {
final int x;
final int? y;
A(this.x, this.y);
}