# AdaptableCustomExpressionFunctionEntry

Canonical page: https://www.adaptabletools.com/docs/reference/adaptablecustomexpressionfunctionentry

A `customStandardFunctions` entry: a full definition, or a partial that
inherits unspecified fields via `extends`.

`extends?: never` on the full branch is a TypeScript discriminant, not a
runtime field. Without it, `A | Partial<A> & { extends: string }` makes
object literals without `extends` fail with &quot;Property &#39;extends&#39; is
missing&quot; instead of checking the full definition.

```ts title="TypeScript"
export type AdaptableCustomExpressionFunctionEntry = (AdaptableCustomExpressionFunction & {
    extends?: never;
}) | AdaptableCustomExpressionFunctionWithExtends;
```

###### References

[`AdaptableCustomExpressionFunction`](https://www.adaptabletools.com/docs/reference/adaptablecustomexpressionfunction.md)