avoid_inconsistent_digit_separators

v1.0.0WarningFixConfigurableFormatting

This rule flags a numeric literal whose _ separators split it into irregularly sized groups.

Why use this rule

1_000_000 is readable because every group is the same size, which is the entire point of the separator: the eye counts groups instead of digits.

10_00_000 defeats that. It looks like a number written in a different convention, and it is exactly how a literal with a wrong digit count survives review — the separator that was supposed to make the magnitude obvious is what hides it.

A literal with no separators at all is never reported. Whether to use them in the first place is a different question, and this rule does not answer it.

The leading group may be shorter than the rest, since that is what is left over: 12_345_678 is correct, 1000_000 is not.

Hexadecimal literals are grouped by hex_group_size (default 4) rather than by thousands, because hex groups by byte or half-word.

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

See also: Dart 3.6 digit separators

Don’t

const population = 10_00_000;   // groups of 2-2-3
const bytes = 1000_000;         // leading group longer than the rest
const mask = 0xFF_FFF_FFF;      // hex grouped by threes

Do

const population = 1_000_000;
const bytes = 1_000_000;
const mask = 0xFFFF_FFFF;

const small = 12_345_678;       // a short leading group is correct

Enabling this rule

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

rules:
  avoid_inconsistent_digit_separators:
    enabled: true

many_lints:
  rules:
    avoid_inconsistent_digit_separators:
      group_size: 3
      hex_group_size: 4

rules:
  avoid_inconsistent_digit_separators:
    group_size: 3
    hex_group_size: 4

Option	Type	Default	Description
`group_size`	int	`3`	Digits per group in a decimal or binary literal
`hex_group_size`	int	`4`	Digits per group in a hexadecimal literal

Set either option to 0 to accept any group size, as long as it is used consistently within the literal.

Turning this rule off

To disable this rule:

rules:
  avoid_inconsistent_digit_separators: false

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

double_literal_format — Write double literals with exactly one leading zero and no redundant trailing zeros.
format_comment — Write comments as capitalised, terminated sentences.
always_pass_global_key — Don’t create a GlobalKey inside build.
always_remove_listener — Ensure every addListener() has a matching removeListener() in dispose().