execute ->> code: return the result
    end

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

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

### 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.

            }
        }

        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>")

        functionCall: FirFunctionCall,
        mode: KtConstantEvaluationMode,
    ): FirLiteralExpression<*>? {
        val function = functionCall.getOriginalFunction() as? FirSimpleFunction ?: return null

        val opr1 = evaluate(functionCall.explicitReceiver, mode) ?: return null
        opr1.evaluate(function)?.let {
            return it.adjustType(functionCall.resolvedType)
        }

        }

        // Preliminary extension function check
        val extensionCandidate = couldBeExtensionFunction && ktFunction.receiverTypeReference != null &&
            method.firstParameterMatches(ktFunction.receiverTypeReference!!) &&
            ktFunction.valueParameters.size == paramCountWithReceiver
        if (!(extensionCandidate || ktFunction.valueParameters.size == paramCount)) {

```

### Advantages of `Annotated`

**Using `Annotated` is recommended** instead of the default value in function parameters, it is **better** for multiple reasons. 🤓

The **default** value of the **function parameter** is the **actual default** value, that's more intuitive with Python in general. 😌

### 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.

        // Expected type of `expression` is `T`
        val function = expression.unwrapQualified<KtFunction> { function, expr -> function.bodyExpression == expr } ?: return null
        if (function.bodyBlockExpression != null) {
            // Given `fun f(...): R { blockExpression }`, `{ blockExpression }` is mapped to the enclosing anonymous function,

In this case, we pass a dependency function `get_current_active_user` to `Security` (the same way we would do with `Depends`).

But we also pass a `list` of scopes, in this case with just one scope: `items` (it could have more).

And the dependency function `get_current_active_user` can also declare sub-dependencies, not only with `Depends` but also with `Security`. Declaring its own sub-dependency function (`get_current_user`), and more scope requirements.

}

/**
 * Returns whether the function uses its body as an expression (i.e., the function uses the result value of the expression) or not.
 *
 * Named functions do not consider their bodies used if
 *  - the function body is a block e.g., `fun foo(): Int { return bar }` or
 *  - the function itself returns Unit
 */