# ExprKind::Tup(_elems) => { None }

### [ExprKind in rustc\_hir](https://doc.rust-lang.org/beta/nightly-rustc/rustc_hir/enum.ExprKind.html)

```rust

Call(&'hir Expr<'hir>, &'hir [Expr<'hir>])
A function call.

The first field resolves to the function itself (usually an ExprKind::Path), and the second field is the list of arguments. This also represents calling the constructor of tuple-like ADTs such as tuple structs and enum variants.
```

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1690729793152/79664806-cce5-4c87-a345-72139e8fb14d.png align="center")

看起来你的匹配表达式需要返回一个 `Option` 类型，但是你的当前实现返回的是 `()` 类型（Rust的空类型）。你需要返回一个合适的 `Option` 类型，例如 `None` 或者 `Some(T)`，其中 `T` 是一个适合你程序的类型。

如果你没有合适的值要返回，你可以简单地返回 `None`，例如：

```rust
            ExprKind::Tup(_elems) => {
                // Do nothing for tuples, return None
                None
            }
```