/**
 * Field accessors shared by every series.
 *
 * Each accepts a key, a dotted path, or a function, so the same option can be
 * written declaratively (`valueField: 'metrics.total'`, which survives
 * serialisation) or imperatively (`valueField: (d) => d.a + d.b`) without the
 * series needing to care which.
 *
 * @module series/accessors
 */
export type FieldAccessor<T> = string | ((datum: unknown) => T | null | undefined);
/** Read a raw field value, resolving dotted paths and accessor functions. */
export declare function readField(source: unknown, field: FieldAccessor<unknown>): unknown;
/**
 * Read a numeric field. Returns null for anything that is not a finite number,
 * so a missing value can never be mistaken for zero.
 */
export declare function readNumber(source: unknown, field: FieldAccessor<number>): number | null;
/** Read a field as a display string, or undefined when absent. */
export declare function readText(source: unknown, field: FieldAccessor<string>): string | undefined;
/** Read a `[lon, lat]` pair, tolerating `{lon, lat}`, `{lng, lat}` and array form. */
export declare function readLonLat(value: unknown): [number, number] | null;
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