double_literal_format

v1.0.0WarningFixConfigurableFormatting

This rule flags a double literal written with a missing leading zero (.5), a redundant leading zero (00.5), or a redundant trailing zero (0.50).

Why use this rule

.5 and 0.50 denote exactly the same numbers as 0.5, so the spelling carries no information and only costs the reader a moment deciding whether it does.

The bare-dot form is the one that actually misleads: .5 reads as a member access until the eye reaches the digit, and a single dropped character turns .5 into an identifier that may still parse.

dart format normalizes none of these, so this rule does not fight the formatter.

A single trailing zero is never reported. 1.0 cannot lose it without becoming 1. (invalid Dart) or the integer 1 (a different type) — and in Flutter code, where 16.0 and 0.0 are everywhere, reporting them would make the rule unusable.

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

See also: Dart language tour — numbers

Don’t

const opacity = .5;      // reads as a member access until the digit arrives
const scale = 0.50;      // the trailing zero says nothing
const ratio = 00.5;      // a typo under any style

Do

const opacity = 0.5;
const scale = 0.5;
const ratio = 0.5;

const padding = 16.0;    // a single trailing zero is significant, never reported

Enabling this rule

This rule is in the pedantic preset, so it is enabled by preset: pedantic or by name:

rules:
  double_literal_format:
    enabled: true

many_lints:
  rules:
    double_literal_format:
      leading_zero: true
      trailing_zero: false

rules:
  double_literal_format:
    leading_zero: true
    trailing_zero: false

Option	Type	Default	Description
`leading_zero`	bool	`true`	Whether `.5` must be written `0.5`
`trailing_zero`	bool	`true`	Whether `0.50` must be written `0.5`

A redundant leading zero (00.5) is reported even with leading_zero: false. That option governs whether .5 is acceptable, which is a style choice; 00.5 is a typo under either style.

Turning this rule off

To disable this rule:

rules:
  double_literal_format: false

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

format_comment — Write comments as capitalised, terminated sentences.
avoid_inconsistent_digit_separators — Group digit separators at a regular interval.
format_test_name — Hold test descriptions to a house pattern.
always_pass_global_key — Don’t create a GlobalKey inside build.