Structured Field Values type mapping

The mapper infers types from CLR property types. An explicit type: ItemType.X selects another compatible wire representation; incompatible combinations fail at mapper construction.

CLR Type	Structured Type	Notes
`int`, `long`	Integer	Range: −999,999,999,999,999 to 999,999,999,999,999
`decimal`	Decimal	Up to 12 integer digits and 3 fractional places
`bool`	Boolean	`?1` / `?0`; bare key in dictionaries = `?1`
`string`	String	Override with `type: ItemType.Token` or `ItemType.DisplayString`
`byte[]`	Byte Sequence	`:base64:` encoding
`long` with `type: ItemType.Date`	Date	Full-range Unix seconds; default `long` mapping remains Integer

Presence

Presence is configured independently using MappingPresence from DamianH.Http.StructuredFieldValues.Mapping:

Presence	Behavior
`Auto` (default)	Non-nullable value properties are required; nullable value and all reference properties are optional. Inner lists are optional.
`Required`	Missing members/parameters fail parsing; null properties fail serialization.
`Optional`	Missing members/parameters leave property initializers unchanged; null properties are omitted.

C# reference-type nullable annotations do not change these defaults. An optional non-nullable value property cannot distinguish absence from its default value.

using DamianH.Http.StructuredFieldValues;
using DamianH.Http.StructuredFieldValues.Mapping;

public class EventMetadata
{
    public string Label { get; init; } = "";
    public string? Kind { get; init; }
    public long Timestamp { get; init; }

    public static readonly StructuredFieldMapper<EventMetadata> Mapper =
        StructuredFieldMapper<EventMetadata>.Dictionary(b => b
            .Member("label", x => x.Label,
                type: ItemType.DisplayString, presence: MappingPresence.Required)
            .Member("kind", x => x.Kind, type: ItemType.Token)
            .Member("at", x => x.Timestamp, type: ItemType.Date));
}

See the API reference for mapper factories, nested item mappings, and serialization constraints.