All the same process that applied for path parameters also applies for query parameters:

* Editor support (obviously)
* Data <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>
* Data validation
* Automatic documentation

## Defaults { #defaults }

    checkHelperVersion(getClass().getClassLoader(), "AtomicReferenceFieldUpdaterAtomicHelper");
    /*
     * Since we use AtomicReferenceFieldUpdaterAtomicHelper by default, we'll "obviously" use it
     * even when Unsafe isn't available. But it's nice to have a check here to make sure that
     * nothing somehow goes wrong as the JDK restricts access to Unsafe.
     */

    // that simply loops through the subscribers and dispatches the event to each would actually
    // probably provide a stronger order guarantee, though that order would obviously be different
    // in some cases.

    /** Global event queue. */
    private final ConcurrentLinkedQueue<EventWithSubscriber> queue = new ConcurrentLinkedQueue<>();

    @Override

You can also read more about them in the <a href="https://en.wikipedia.org/wiki/Environment_variable" class="external-link" target="_blank">Wikipedia for Environment Variable</a>.

In many cases it's not very obvious how environment variables would be useful and applicable right away. But they keep showing up in many different scenarios when you are developing, so it's good to know about them.

		if !srcEOF && srcCtnt.Err != nil {
			log.Fatal(srcCtnt.Err)
		}

		if !tgtEOF && tgtCtnt.Err != nil {
			log.Fatal(tgtCtnt.Err)
		}

		// If source doesn't have objects anymore, comparison becomes obvious
		if srcEOF {
			fmt.Printf("only in target: %s\n", tgtCtnt.Key)
			tgtCtnt, tgtOk = <-tgtCh
			continue
		}

		// The same for target
		if tgtEOF {
			fmt.Printf("only in source: %s\n", srcCtnt.Key)

Temporarily adopting this point of view (of the *external developer*) can help you feel like it's more obvious where to put the parameters, the Pydantic model for the body, for the response, etc. for that *external API*.

///

### Create a callback `APIRouter` { #create-a-callback-apirouter }