---
type: "fhir-fhirpath-function"
title: "FHIR FHIRPath Function: %factory.withExtension"
source: "source/fhirpath.html"
---

# FHIR FHIRPath Function: %factory.withExtension

This page is part of **FHIR FHIRPath** (FHIR-specific extensions). Base spec lives at [FHIRPath](/fhirpath).

`%factory.withExtension(instance : T, url : string, value) : T`

Add an extension, and return the new type: `%factory.withExtension(%factory.create(Money), 'http:/acme.com/extension/example', %factory.code('test'))`

Parameters:

-   **instance**: The instance to add the URL to
-   **url**: a string value that goes in Extension.url
-   **value**: the value of the extension

**Return Value:** A copy of the instance of the type with the extension added. Extensions that already exist with the same url are not removed.

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[Back to FHIR FHIRPath](/fhir-fhirpath)