is this a default in Dart compiler? - dart

Question

I spend some hours to find an error in a dart program.
At most simple I found something like :
class User{
String name;
User(String name){
name = "user +$name";
}
}
It should have been _name for the internal property, but a developer forgets this rule.
The code gives a null result to:
User u1 = new User("U1");
print(u1.name);
> null
My question is :
I find it strange that the compiler allows reusing the same var name in call parameters and inside the code without any warning.
I think that if some parameter is like here *User(String name) *, the further use of name should be read-only.
Is this a weakness of language?
Have you seen the same PB in other languages?

Answer 1

I can see where you are coming from but this is the same scoping rules as Java (and properly also C#?) and normal behavior for parameters for methods and constructors.
I think that reassign a parameter with another value is bad behavior and you can get the analyzer to detect that with adding the following linter rule to analysis_options.yaml:
linter:
rules:
parameter_assignments
The rule are described here:
http://dart-lang.github.io/linter/lints/parameter_assignments.html
But I can see this rule are not used for constructors which are your case and I would guess that this is a bug to the linter or a case where there should be another rule to detect parameter assignments for constructors. I would therefore suggest you create an issue here: https://github.com/dart-lang/linter/issues
The read only behavior for parameters (both for methods and constructors) can be achieved by using final for each parameter as:
User(final String name) {
name = 'user +$name'; // error: 'name' a final variable can only be set once
}
But that is not really practical in the sense where you want to prevent accidents where the developer forget to do something.
And just for the record, you can assign the name value in the User class by doing this (if you still want the parameter and class variable to have the same name):
class User {
String name;
User(String name) {
this.name = 'user +$name';
}
}