falcon

Rules / Style / prefer-initializing-formals

prefer-initializing-formals

lint/style/prefer-initializing-formals
recommended
Same as prefer_initializing_formals · Dart lints

Flags a constructor that copies a plain parameter into a same-named field.

Dart's initializing formals (this.x) declare the parameter and assign the field in one step, so the manual copy — whether an initializer-list entry : x = x or a body statement this.x = x; — is redundant boilerplate. The rule is intentionally narrow: it fires only when the parameter name exactly matches the field name and the parameter is a plain constructor parameter, never an existing initializing (this.) or super (super.) formal, so cases that already use the idiom or that transform the value are left untouched.

Invalid

example.dartdart
// Parameters copied verbatim into same-named fields.
class A {
  int x;
  A(int x) : x = x;
}

class B {
  int y;
  B(int y) { this.y = y; }
}

class C {
  int a, b;
  C(int a, int b) : a = a, b = b;
}

class D {
  String name;
  D(String name) : name = name;
}

class E {
  int v;
  E(int v) { this.v = v; }
}
Use an initializing formal to assign a parameter to a field.
3 int x;
4 A(int x) : x = x;
Use an initializing formal to assign a parameter to a field.
8 int y;
9 B(int y) { this.y = y; }
Use an initializing formal to assign a parameter to a field.
13 int a, b;
14 C(int a, int b) : a = a, b = b;
Use an initializing formal to assign a parameter to a field.
13 int a, b;
14 C(int a, int b) : a = a, b = b;
Use an initializing formal to assign a parameter to a field.
18 String name;
19 D(String name) : name = name;
Use an initializing formal to assign a parameter to a field.
23 int v;
24 E(int v) { this.v = v; }

Valid

example.dartdart
// Uses initializing formals, or assignments that are not a verbatim copy.
class A {
  int x;
  A(this.x);
}

class B {
  int y;
  B(int value) : y = value;
}

class C {
  int a;
  C(int a) : a = a + 1;
}

class D {
  int v;
  D(this.v);
}

class E {
  int w;
  E(int input) { w = input; }
}

class F {
  int z;
  F(this.z) { print(z); }
}

How to configure

Set the severity of prefer-initializing-formals in your falcon.json:

falcon.jsonjson
{
  "linter": {
    "rules": {
      "style": {
        "prefer-initializing-formals": "error"
      }
    }
  }
}

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