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Expand "thiserror and anyhow" slide (#1600)

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Explain what traits `thiserror::Error` derives.

Explain how `.context()` and `.with_context()` operate on types that are
not aware of `anyhow`.

Resolves #1597.
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Pavel Roskin 2023-12-20 07:37:22 -08:00 committed by GitHub
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src/error-handling/thiserror-and-anyhow.md
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@ -41,13 +41,22 @@ fn main() {
<details>
## `thiserror`
* The `Error` derive macro is provided by `thiserror`, and has lots of useful
attributes like `#[error]` to help define a useful error type.
* `anyhow::Result<V>` is a type alias for `Result<V, anyhow::Error>`.
attributes to help define error types in a compact way.
* The `std::error::Error` trait is derived automatically.
* The message from `#[error]` is used to derive the `Display` trait.
## `anyhow`
* `anyhow::Error` is essentially a wrapper around `Box<dyn Error>`. As such it's again generally not
a good choice for the public API of a library, but is widely used in applications.
* `anyhow::Result<V>` is a type alias for `Result<V, anyhow::Error>`.
* Actual error type inside of it can be extracted for examination if necessary.
* Functionality provided by `anyhow::Result<T>` may be familiar to Go developers, as it provides
similar usage patterns and ergonomics to `(T, error)` from Go.
* `anyhow::Context` is a trait implemented for the standard `Result` and `Option` types.
`use anyhow::Context` is necessary to enable `.context()` and `.with_context()` on those types.
</details>