# `Ordinal` types and collections
The library provides `Ordinal` trait to map types to `usize` values,
proc-macro to derive `Ordinal` trait for structs and enums,
and `map` and `set` implementations
that use these types as keys efficiently.
## Example
```rust
use ordinal_map::map::total::OrdinalTotalMap;
#[derive(ordinal_map::Ordinal)]
enum ErrorCategory {
Network,
Disk,
Logic,
}
fn classify_error(error: &str) -> ErrorCategory {
// ...
}
let mut error_counts: OrdinalTotalMap<ErrorCategory, u64> = OrdinalTotalMap::default();
for error in &errors {
let category = classify_error(error);
error_counts[category] += 1;
}
```