PartialOrd

The PartialOrd macro generates a compareTo() method for partial ordering comparison. This is analogous to Rust’s PartialOrd trait, enabling comparison between values where some pairs may be incomparable.

Generated Output

Type	Generated Code	Description
Class	`classNamePartialCompare(a, b)` + `static compareTo(a, b)`	Standalone function + static wrapper method
Enum	`enumNamePartialCompare(a, b): number \\| null`	Standalone function returning `number \\| null`
Interface	`ifaceNamePartialCompare(a, b): number \\| null`	Standalone function returning `number \\| null`
Type Alias	`typeNamePartialCompare(a, b): number \\| null`	Standalone function returning `number \\| null`

Names use camelCase conversion (e.g., Temperature → temperaturePartialCompare).

Return Values

Unlike Ord, PartialOrd returns number | null to handle incomparable values:

-1: a is less than b
0: a is equal to b
1: a is greater than b
null: Values are incomparable

When to Use PartialOrd vs Ord

PartialOrd: When some values may not be comparable
- Example: Floating-point NaN values
- Example: Mixed-type unions
- Example: Type mismatches between objects
Ord: When all values are guaranteed comparable (total ordering)

Comparison Strategy

Fields are compared lexicographically in declaration order:

Compare first field
If incomparable, return null
If not equal, return that result
Otherwise, compare next field
Continue until a difference is found or all fields are equal

Type-Specific Comparisons

Type	Comparison Method
`number`/`bigint`	Direct subtraction (`a - b`)
`string`	`localeCompare()`
`boolean`	`false < true` (cast to number)
null/undefined	Returns `null` for mismatched nullability
Arrays	Lexicographic, propagates `null` on incomparable elements
`Date`	Timestamp comparison, `null` if invalid
Objects	Delegates to `compareTo()` if available

Field-Level Options

The @ord decorator supports:

skip - Exclude the field from ordering comparison

Example

Before (Your Code)

/** @derive(PartialOrd) */
class Temperature {
    value: number | null;
    unit: string;
}

After (Generated)

class Temperature {
    value: number | null;
    unit: string;

    static compareTo(a: Temperature, b: Temperature): number | null {
        return temperaturePartialCompare(a, b);
    }
}

export function temperaturePartialCompare(a: Temperature, b: Temperature): number | null {
    if (a === b) return 0;
    const cmp0 = (() => {
        if (typeof (a.value as any)?.compareTo === 'function') {
            const optResult = (a.value as any).compareTo(b.value);
            return optResult === null ? null : optResult;
        }
        return a.value === b.value ? 0 : null;
    })();
    if (cmp0 === null) return null;
    if (cmp0 !== 0) return cmp0;
    const cmp1 = a.unit.localeCompare(b.unit);
    if (cmp1 === null) return null;
    if (cmp1 !== 0) return cmp1;
    return 0;
}

Return Type

The generated functions return number | null where null indicates incomparable values.