export type ValueType = 'string' | 'boolean' | 'number';
export type DefaultValue = string | boolean | number | undefined;
interface TypeMap<Default> {
    string: Default extends undefined ? string | undefined : string;
    boolean: Default extends undefined ? boolean | undefined : boolean;
    number: Default extends undefined ? number | undefined : number;
}
type EnvReturn<Value extends ValueType, Default extends DefaultValue> = TypeMap<Default>[Value];
export declare class EnvError extends Error {
    code: string;
    constructor(message: string, code?: string);
}
export declare function env<Value extends ValueType, Default extends DefaultValue>(key: string, valueType: Value, defaultValue?: Default): EnvReturn<Value, Default>;
export {};