What is the syntax for Typescript arrow functions with generics?

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Edit

Per @Thomas comment, in newer TS compilers, we can simply do:

const foo = <T,>(x: T) => x;

Original Answer

The full example explaining the syntax referenced by Robin… brought it home for me:

Generic functions

Something like the following works fine:

function foo<T>(x: T): T { return x; }

However using an arrow generic function will not:

const foo = <T>(x: T) => x; // ERROR : unclosed `T` tag

Workaround: Use extends on the generic parameter to hint the compiler
that it’s a generic, e.g.:

const foo = <T extends unknown>(x: T) => x;

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