unacy / Formatter

Type Alias: Formatter<TInput>

type Formatter<TInput> = (input) => string;

Defined in: packages/core/src/formatters.ts:46

Formatter converts a format-tagged value to a string representation.

Type Parameters

Type Parameter	Description
TInput extends WithFormat<unknown, string>	Format-tagged type to format (must extend WithFormat<T, F>)

Parameters

Parameter	Type	Description
input	TInput	Value tagged with the format brand

Returns

string

Plain string representation (format brand is stripped in the output)

Remarks

• Output string should be parseable by the corresponding Parser<TInput> to ensure round-trip integrity
• The format brand carried by TInput is lost in the string output; callers must re-parse to recover a branded value

Example

type ISO8601Date = WithFormat<Date, 'ISO8601'>;
const formatISO: Formatter<ISO8601Date> = (date) => date.toISOString();

Use When

You need a typed function that can only receive format-validated values (via WithFormat<T, F>) before serialising them.

Avoid When

The value needs no format brand — accept a plain T and format without the tag overhead.

Pitfalls

NEVER call a Formatter on a plain (untagged) value without first wrapping it in the appropriate WithFormat<T, F> brand via a Parser — the brand exists to guarantee the value has been validated before formatting.

NEVER assume formatter output is stable across timezone environments — Date.toISOString() uses UTC but other formatters may be locale-sensitive.

See

• Parser
• FormatterParser