prefer-function-type

Prefer function types over single-signature structural types

A structural type containing only one callable signature adds structure without expressing another capability.
Instead, you SHOULD write the callable directly as a function or constructor type.

Nominal, inherited, and overloaded callable types retain their declarations.

- Category: style
- Level: warning
- Fix: automatic
- Scope: module

Reported

type Transform = { (value: int32): string };
Accepted

type Transform = (value: int32) => string;
Prior art

- typescript-eslint · prefer-function-type

language/linter/src/rules/style/preferfunctiontype.rs:9