## Use Case

Let's start with an example **use case** and then see how to solve it with this.

Let's imagine that you have some **machine learning models** that you want to use to handle requests. 🤖

The same models are shared among requests, so, it's not one model per request, or one per user or something similar.

        }

        resolvedSymbols.firstIsInstanceOrNull<KtCallableSymbol>()?.firSymbol?.let { availableCallable ->
            return canShorten(fqName, availableCallable.callableId.asSingleFqName()) { callableShortenStrategy(availableCallable) }
        }

        resolvedSymbols.firstIsInstanceOrNull<KtClassLikeSymbol>()?.firSymbol?.let { availableClassifier ->

你可以用作 TLS 终止代理的一些选项包括：

* Traefik（也可以处理证书更新）
* Caddy（也可以处理证书更新）
* Nginx
* HAProxy

## Let's Encrypt

在 Let's Encrypt 之前，这些 **HTTPS 证书** 由受信任的第三方出售。

过去，获得这些证书的过程非常繁琐，需要大量的文书工作，而且证书非常昂贵。

但随后 **<a href="https://letsencrypt.org/" class="external-link" target="_blank">Let's Encrypt</a>** 创建了。

它是 Linux 基金会的一个项目。 它以自动方式免费提供 **HTTPS 证书**。 这些证书可以使用所有符合标准的安全加密，并且有效期很短（大约 3 个月），因此**安全性实际上更好**，因为它们的生命周期缩短了。

    (this as? FirResolvedNamedReference)?.resolvedSymbol

internal fun FirReference.getResolvedKtSymbolOfNameReference(builder: KtSymbolByFirBuilder): KtSymbol? =
    getResolvedSymbolOfNameReference()?.fir?.let(builder::buildSymbol)

internal fun FirErrorNamedReference.getCandidateSymbols(): Collection<FirBasedSymbol<*>> =
    diagnostic.getCandidateSymbols()

### Include an `APIRouter` with a custom `prefix`, `tags`, `responses`, and `dependencies`

Now, let's imagine your organization gave you the `app/internal/admin.py` file.

It contains an `APIRouter` with some admin *path operations* that your organization shares between several projects.

    {!> ../../../docs_src/python_types/tutorial008.py!}
    ```

This means:

* The variable `prices` is a `dict`:
    * The keys of this `dict` are of type `str` (let's say, the name of each item).
    * The values of this `dict` are of type `float` (let's say, the price of each item).

#### Union

You can declare that a variable can be any of **several types**, for example, an `int` or a `str`.

Let's look at how we can make that work.

## pytest.mark.anyio

            type.isDouble -> KtConstantValue.KtDoubleConstantValue((value as Number).toDouble(), expression)
            else -> null
        }

        return constantValue?.let { KtConstantAnnotationValue(it, analysisSession.token) }
    }

    private fun Collection<FirExpression>.convertVarargsExpression(
        builder: KtSymbolByFirBuilder,
    ): Pair<Collection<KtAnnotationValue>, KtElement?> {

            }
        }

    override fun createPointer(): KtSymbolPointer<KtConstructorSymbol> = withValidityAssertion {
        KtPsiBasedSymbolPointer.createForSymbolFromSource<KtConstructorSymbol>(this)?.let {
            return it
        }

        val callableId = descriptor.callableIdIfNotLocal
        if (callableId != null) {
            val signature = descriptor.getSymbolPointerSignature()

                    .let(::FqName)
            }
        }
    }

    private fun collectTypeReferences(qualified: KtUserType): MutableList<KtNameReferenceExpression> {
        val refs = mutableListOf<KtNameReferenceExpression>()
        fun collectFragments(type: KtUserType) {
            type.getStubOrPsiChild(KtStubElementTypes.USER_TYPE)?.let { collectFragments(it) }