else -> null
        }
    }

    private fun provideSourceForInvokeFunction(function: FirSimpleFunction): PsiElement? {
        val classId = function.containingClassLookupTag()?.classId ?: return null
        val classOrObject = classByClassId(classId, function.llFirSession.ktModule) ?: return null
        return classOrObject.declarations.singleOrNull()
    }

### Step 4: define the **path operation function**

This is our "**path operation function**":

* **path**: is `/`.
* **operation**: is `get`.
* **function**: is the function below the "decorator" (below `@app.get("/")`).

```Python hl_lines="7"
{!../../../docs_src/first_steps/tutorial001.py!}
```

This is a Python function.

# Response Model - Return Type

You can declare the type used for the response by annotating the *path operation function* **return type**.

You can use **type annotations** the same way you would for input data in function **parameters**, you can use Pydantic models, lists, dictionaries, scalar values like integers, booleans, etc.

=== "Python 3.10+"

    ```Python hl_lines="16  21"
    {!> ../../../docs_src/response_model/tutorial001_01_py310.py!}
    ```

## Get the user

Now create a function that will:

* Take a username.
* Generate a document ID from it.
* Get the document with that ID.
* Put the contents of the document in a `UserInDB` model.

## Create a middleware

To create a middleware you use the decorator `@app.middleware("http")` on top of a function.

The middleware function receives:

* The `request`.
* A function `call_next` that will receive the `request` as a parameter.
    * This function will pass the `request` to the corresponding *path operation*.
    * Then it returns the `response` generated by the corresponding *path operation*.

### Custom Generate Unique ID Function

FastAPI uses a **unique ID** for each *path operation*, it is used for the **operation ID** and also for the names of any needed custom models, for requests or responses.

You can customize that function. It takes an `APIRoute` and outputs a string.

participant code as Code
participant function as say_hi()
participant execute as Execute function

    rect rgba(0, 255, 0, .1)
        code ->> function: say_hi(name="Camila")
        function ->> execute: execute function code
        execute ->> code: return the result
    end

    rect rgba(0, 255, 255, .1)
        code ->> function: say_hi(name="Camila")
        function ->> code: return stored result
    end

# Background Tasks - `BackgroundTasks`

You can declare a parameter in a *path operation function* or dependency function with the type `BackgroundTasks`, and then you can use it to schedule the execution of background tasks after the response is sent.

You can import it directly from `fastapi`:

```python
from fastapi import BackgroundTasks
```

            }
        }

        if (declaration is KtFunction && declaration !is KtConstructor<*> && declaration.equalsToken != null) {
            val bindingContext = analysisContext.analyze(declaration)
            val kotlinType = bindingContext[BindingContext.FUNCTION, declaration]?.returnType
                ?: ErrorUtils.createErrorType(ErrorTypeKind.IMPLICIT_RETURN_TYPE_FOR_FUNCTION, declaration.name ?: "<unknown>")

import kotlin.annotation.AnnotationRetention.BINARY
import kotlin.annotation.AnnotationTarget.CLASS
import kotlin.annotation.AnnotationTarget.CONSTRUCTOR
import kotlin.annotation.AnnotationTarget.FUNCTION

@Retention(BINARY)
@Documented
@Target(CONSTRUCTOR, CLASS, FUNCTION)