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/**
 * Factory methods for common validation functions. The numerical methods only support Int, Long,
 * Float, and Double.
 */
public class ParamValidators {
    // Always return true.
    public static <T> ParamValidator<T> alwaysTrue() {...}

    // Check if the parameter value is greater than lowerBound.
    public static <T> ParamValidator<T> gt(double lowerBound) {...}

    // Check if the parameter value is greater than or equal to lowerBound.
    public static <T> ParamValidator<T> gtEq(double lowerBound) {...}

    // Check if the parameter value is less than upperBound.
    public static <T> ParamValidator<T> lt(double upperBound) {...}

    // Check if the parameter value is less than or equal to upperBound.
    public static <T> ParamValidator<T> ltEq(double upperBound) {...}

    /**
     * Check if the parameter value is in the range from lowerBound to upperBound.
     *
     * @param lowerInclusive if true, range includes value = lowerBound
     * @param upperInclusive if true, range includes value = upperBound
     */
    public static <T> ParamValidator<T> inRange(double lowerBound, double upperBound, boolean lowerInclusive, boolean upperInclusive) {...}

    // Check if the parameter value is in the range [lowerBound, upperBound].
    public static <T> ParamValidator<T> inRange(double lowerBound, double upperBound) {...}

    // Check if the parameter value is in the array of allowed values.
    public static <T> ParamValidator<T> inArray(T... allowed) {...}

    // Check if the parameter value is not null.
    public static <T> ParamValidator<T> notNull() {...}
}

Proposed Changes

We make the following notes regarding the implementation and the usage of the proposed interfaces:

1) With the proposed public interface, users algorithm developers can define a parameter multiple parameters by simply calling e.g. Param<Boolean> BOOLEAN_PARAM = new BooleanParam(...), . And in order to have WithParams::getParamMap() return those parameter values, regardless of whether algorithm users have explicitly called WithParams::set(...) to set parameter values, algorithm developer should make sure to initialize the paramMap in the constructor.

This can be achieved by calling the util method ParamUtils.initializeMapWithDefaultValues(paramMap, withParamsInstance).

2) The initializeMapWithDefaultValues(paramMap, withParamsInstancewithout calling extra methods to register this parameter object to another collection object (e.g. map). The getParamMap(...) method will use Java reflection to enumerate all public fields of this instance withParamInstance, find those fields assignable from the Param class, and returns a map that contains the parameter values for all those Param fieldsupdate the given paramMap with default value for those Param fields that are not already found in the paramMap.

In order for this to work correctly, initializeMapWithDefaultValues(...) should be called after all public Param-typed fields of the given WithParams instance have been defined. A good choice is to call this method in the constructor of the WithParams instance.

Example Usage

In the following we provide an example code snippet that shows how to define, set and get parameter values with various types.

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