export default class Env<T extends {
    string?: string;
    integer?: string;
    boolean?: string;
}, StringEnvs extends string = T['string'] extends string ? T['string'] : never, IntegerEnvs extends string = T['integer'] extends string ? T['integer'] : never, BooleanEnvs extends string = T['boolean'] extends string ? T['boolean'] : never> {
    get isProduction(): boolean;
    get nodeEnv(): StandardNodeEnvValues;
    get isTest(): boolean;
    get isDevelopment(): boolean;
    get isDevelopmentOrTest(): boolean;
    string<OptionalConfig extends {
        optional: boolean;
    } | undefined, ReturnType extends OptionalConfig extends undefined ? string : OptionalConfig extends {
        optional: boolean;
    } ? OptionalConfig['optional'] extends true ? string | undefined : string : string>(env: StringEnvs, opts?: OptionalConfig): ReturnType;
    integer<OptionalConfig extends {
        optional: boolean;
    } | undefined, ReturnType extends OptionalConfig extends undefined ? number : OptionalConfig extends {
        optional: boolean;
    } ? OptionalConfig['optional'] extends true ? number | undefined : number : number>(env: IntegerEnvs, opts?: OptionalConfig): ReturnType;
    /**
     * Reads a boolean environment variable. Only the exact string `"1"` is
     * true. Every other value is false, including `"true"`, `"TRUE"`, `"yes"`
     * and `""`, and so is an unset variable.
     *
     * ```ts
     * // FEATURE_FLAG=1
     * AppEnv.boolean('FEATURE_FLAG') // true
     *
     * // FEATURE_FLAG=true
     * AppEnv.boolean('FEATURE_FLAG') // false
     * ```
     *
     * @param env - the name of the environment variable
     * @returns `true` when the variable is exactly `"1"`, otherwise `false`
     */
    boolean(env: BooleanEnvs): boolean;
    setString(env: StringEnvs, val: string | undefined): void;
    unsetString(env: StringEnvs): void;
    setInteger(env: IntegerEnvs, val: number | undefined): void;
    unsetInteger(env: IntegerEnvs): void;
    /**
     * Sets a boolean environment variable to `"1"`, the only value
     * {@link Env.boolean} reads as true.
     *
     * @param env - the name of the environment variable
     */
    setBoolean(env: BooleanEnvs): void;
    /**
     * Deletes a boolean environment variable. {@link Env.boolean} reads an
     * unset variable as false, since only the exact string `"1"` is true.
     *
     * @param env - the name of the environment variable
     */
    unsetBoolean(env: BooleanEnvs): void;
    protected required(variable: string): string;
    protected optional(variable: string): string | undefined;
}
export type StandardNodeEnvValues = 'production' | 'development' | 'test';