Strongly-typed string keys for configuration.
A frequent task is to extract a typed value from an untyped
Map<String, Object>. Typically, this is done via string keys:
let port: u32 = map.get("port")?.parse()?. A slightly more type-safe approach is to associate certain types with corresponding string constants:
#[macro_use] extern crate typed_key; use typed_key::Key; // `PORT` is basically `"port"` string with associated `u32` type. const PORT: Key<u32> = typed_key!("port");
This crate provides basic building block for such strongly-typed strings. See example for a complete example of reading configuration, and the blog post for a more long winded explanation of the pattern.
Using string keys is totally fine for small isolated cases, but if this pattern is pervasive,
typed_key can provide the following benefits:
- Documentation: all possible keys are declared in one place, specify their type explicitly, and can have documentation comments.
- Type safety: because each key carries its type, it's impossible to read the value of wrong type. Unlike string keys, typed keys never need a turbofish operator.
- Typo safety: you can't misspell a type key on the call site.
- Navigation: with typed_keys, you can use "go to definition", "find usages", and refactor without fear.