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Many Lints

prefer_named_parameters

v1.0.0WarningConfigurableCode Quality

This rule flags a declaration taking more than a few positional parameters.

This rule is in the pedantic preset: the budget is a house style.

Why use this rule

Section titled “Why use this rule”

move(3, 4, 5) tells the reader nothing, and swapping two arguments of the same type compiles cleanly and fails at runtime. Named parameters put the meaning at the call site, where it is read.

The threshold matters more than the principle. One or two positional parameters are usually the subject of the call — substring(0, 4), Point(x, y) — and naming them is noise, so the default budget is 2.

Exempt by default:

  • An @override, whose signature belongs to the supertype, and an operator, whose parameters cannot be named.
  • A private constructor. It is not an API: it is reached from one place in the same library, usually a factory assembling injected dependencies (Pipeline._(this._storage, this._adapter, this._policy)), and naming those adds ceremony at the one call site that already knows the order.
  • main, onRequest and middleware, whose positional signature a framework dictates. dart_frog passes the URL’s path segments in order, so naming them is not the author’s to decide.

Those last two accounted for 22 of 28 reports on a real codebase.

See also: Effective Dart: parameters

Don’t

Section titled “Don’t”
void move(int x, int y, int z) {}

Do

Section titled “Do”
void move({required int x, required int y, required int z}) {}


// One or two positional parameters are the subject of the call.
String slice(String value, int start) => value;

Options

Section titled “Options”
analysis_options.yaml
many_lints:
  rules:
    prefer_named_parameters:
      max_positional: 2
      additional_ignored_names: [handleRequest]
      ignore_private_constructors: true
Option Type Default Description
max_positional int 2 Most positional parameters a declaration may take
ignored_names list of strings [main, onRequest, middleware] Declarations whose signature a framework dictates
additional_ignored_names list of strings [] Names to add to that list
ignore_private_constructors bool true Skip Type._(...), which is not an API

Turning this rule off

Section titled “Turning this rule off”

To disable this rule:

many_lints.yaml
rules:
  prefer_named_parameters: false

To keep the rule on but skip certain paths, use per-rule exclude.

Section titled “Related rules”