Skip to main content

no-t

Disallow single-character generic type parameter names.

This rule helps keep type parameter names self-documenting and easier to read in larger codebases.

Targeted pattern scope​

This rule targets type parameter identifiers in generic declarations.

It reports:

  • single-character names (for example T, K, U), and
  • names with two or more characters that do not start with configured prefix (when prefix is set).

What this rule reports​

  • Generic type parameters with a single-character name (for example T, U, K).
  • Optional: type parameter names that do not use a configured prefix.

Why this rule exists​

Single-character type parameter names are terse but often ambiguous outside narrowly scoped declarations. Descriptive names improve readability and maintenance.

❌ Incorrect​

function identity<T>(value: T): T {
 return value;
}

✅ Correct​

function identity<ValueType>(value: ValueType): ValueType {
 return value;
}

Behavior and migration notes​

This rule reports only and does not provide an autofix.

Adopt in warning mode first, then rename generic parameters to descriptive names in touched code paths.

Options​

type Options = [
 {
  prefix?: string;
 }?,
];

Default configuration​

[{}];

prefix​

Type: string

When configured, all type parameter names longer than one character must start with the specified prefix.

Example configuration:

"etc-misc/no-t": ["error", { prefix: "Type" }];

Additional examples​

// config: { prefix: "Type" }
function map<TypeInput, TypeOutput>(value: TypeInput): TypeOutput {
 return value as unknown as TypeOutput;
}
// ✅ valid

function map<Input, Output>(value: Input): Output {
 return value as unknown as Output;
}
// ❌ reported because names do not start with "Type"

ESLint flat config example​

import etcMisc from "eslint-plugin-etc-misc";

export default [
 {
  plugins: { "etc-misc": etcMisc },
  rules: {
   "etc-misc/no-t": "error",
  },
 },
];

When not to use it​

Disable this rule if your project intentionally follows short generic naming conventions (for example, single-letter parameters in mathematical or algorithm-heavy APIs).

Package documentation​

Rule catalog ID: R043

Further reading​

Adoption resources​

  • Start at warning level in CI, then move to error after cleanup.
  • Use focused codemods/autofix batches per package or directory.