com.github.dakusui.pcond.forms

Class Functions

java.lang.Object

com.github.dakusui.pcond.forms.Functions

public class Functions
extends Object

An entry point for acquiring function objects. Functions retrieved by methods in this class are all "printable".

Method Summary

Modifier and Type	Method and Description
static <E> Function<E[],List<E>>	arrayToList() Returns a function that converts a given array into a list.
static <T,R> Function<T,R>	call(MethodQuery methodQuery) Returns a Function created from a method specified by a methodQuery.
static <T,R> Function<T,R>	call(String methodName, Object... arguments) Returns a function that calls a method which matches the given methodName and args on the object given as input to it.
static <E> Function<? super Object,E>	cast(Class<E> type) Returns a function that casts an object into a given class.
static <E> Function<? super Object,E>	castTo(E value) Returns a function that casts an object into a given class.
static MethodQuery	classMethod(Class<?> targetClass, String methodName, Object... arguments) Creates a MethodQuery object from given arguments to search for static methods.
static <I extends Collection<E>,E> Function<I,List<E>>	collectionToList() Returns a function that creates and returns a list that contains all the elements in the given list.
static Function<String,Integer>	countLines() Returns a function the counts lines in a given string.
static CurriedFunction<Object,Object>	curry(Class<?> aClass, String methodName, Class<?>... parameterTypes) Curries a static method specified by the given arguments.
static CurriedFunction<Object,Object>	curry(MultiFunction<Object> function) Curries a given multi-function.
static <E> Function<List<E>,E>	elementAt(int i)
static <T,E extends Throwable> Function<T,E>	expectingException(Class<E> exceptionClass, Function<? super T,?> func) Returns a function that converts an input value to an exception object, which is thrown by func, when it is applied.
static Function<String,String>	findString(String substring) The returned function tries to find a substring after a given string.
static <E> Function<E,E>	identity() Returns a printable function that returns a given object itself.
static MethodQuery	instanceMethod(Object targetObject, String methodName, Object... arguments) Creates a MethodQuery object from given arguments to search for static methods.
static Function<? super String,Integer>	length() Returns a function that gives a length of a string passed as an argument.
static <R> MultiFunction<R>	multifunction(Class<?> aClass, String methodName, Class<?>... parameterTypes)
static Parameter	parameter() Returns a Parameter object, which is used in combination with instanceMethod(Object, String, Object[]), classMethod(Class, String, Object[]), or their shorthand methods.
static <E> Function<Collection<E>,Integer>	size() Returns a function that that returns a size of a given list.
static <E> Function<Collection<? extends E>,Stream<E>>	stream() Returns a function that returns a stream for a given collection.
static <E> Function<Collection<? extends E>,Stream<E>>	stream(Class<E> elementClass) Returns a function that returns a stream for a given collection.
static <E> Function<E,Stream<E>>	streamOf() Returns a function that returns a stream for a given object.
static <E> Function<E,String>	stringify() Returns a function that gives a string representation of a object given to it.
static <E> E	value() A method to return a value for a "casting placeholder value".

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

identity

public static <E> Function<E,E> identity()

Returns a printable function that returns a given object itself.

Type Parameters:

E - The type of the object.

Returns:

The function.

stringify

public static <E> Function<E,String> stringify()

Returns a function that gives a string representation of a object given to it. Internally, the returned function calls toString method on a given object.

Type Parameters:

E - The type of the object

Returns:

The function.

length

public static Function<? super String,Integer> length()

Returns a function that gives a length of a string passed as an argument.

Returns:

The function.

elementAt

public static <E> Function<List<E>,E> elementAt(int i)

size

public static <E> Function<Collection<E>,Integer> size()

Returns a function that that returns a size of a given list.

Returns:

The function.

stream

public static <E> Function<Collection<? extends E>,Stream<E>> stream()

Returns a function that returns a stream for a given collection.

Type Parameters:

E - Type of elements in the given collection.

Returns:

The function.

stream

public static <E> Function<Collection<? extends E>,Stream<E>> stream(Class<E> elementClass)

Returns a function that returns a stream for a given collection.

Type Parameters:

E - A type of elements in a collection.

Parameters:

elementClass - A parameter to let compiler know the type of the element in a collection.

Returns:

The function.

streamOf

public static <E> Function<E,Stream<E>> streamOf()

Returns a function that returns a stream for a given object. This method corresponds to Stream.of(Object) method.

Type Parameters:

E - Type of object.

Returns:

The function.

cast

public static <E> Function<? super Object,E> cast(Class<E> type)

Returns a function that casts an object into a given class.

Type Parameters:

E - The type to which the object is case.

Parameters:

type - The type to which the given object is cast

Returns:

The function.

castTo

public static <E> Function<? super Object,E> castTo(E value)

Returns a function that casts an object into a given class.

    assertThat(
        asList(lastName, fullName),
        allOf(
            transform(elementAt(0).andThen(cast(String.class))).check(allOf(isNotNull(), not(isEmptyString()))),
            transform(elementAt(1).andThen(castTo((List<String>)value()))).check(Predicates.contains(lastName))));
 ```

Type Parameters:

E - The type to which the object is case.

Parameters:

value - A type place-holder. Always use a value returned from value() method.

Returns:

The function.

collectionToList

public static <I extends Collection<E>,E> Function<I,List<E>> collectionToList()

Returns a function that creates and returns a list that contains all the elements in the given list.

Type Parameters:

I - The type of the input collection.

E - Type of the elements in the collection

Returns:

The function.

arrayToList

public static <E> Function<E[],List<E>> arrayToList()

Returns a function that converts a given array into a list.

Type Parameters:

E - Type of elements in a given array.

Returns:

The function.

countLines

public static Function<String,Integer> countLines()

Returns a function the counts lines in a given string.

Returns:

The function.

findString

public static Function<String,String> findString(String substring)

The returned function tries to find a substring after a given string. If found, it returns the result of the following statement.

s.substring(s.indexOf(substring) + substring.length())

If not found, a StringIndexOutOfBoundsException will be thrown.

Parameters:

substring - A substring to find in a given string.

Returns:

The string after the substring.

curry

public static CurriedFunction<Object,Object> curry(Class<?> aClass,
                                                   String methodName,
                                                   Class<?>... parameterTypes)

Curries a static method specified by the given arguments.

Parameters:

aClass - A class to which the method to be curried belongs to.

methodName - A name of the method to be curried.

parameterTypes - Parameters types of the method.

Returns:

A printable and curried function of the target method.

curry

public static CurriedFunction<Object,Object> curry(MultiFunction<Object> function)

Curries a given multi-function.

Parameters:

function - A multi-function to be curried

Returns:

A curried function

See Also:

curry(Class, String, Class[])

multifunction

public static <R> MultiFunction<R> multifunction(Class<?> aClass,
                                                 String methodName,
                                                 Class<?>... parameterTypes)

call

public static <T,R> Function<T,R> call(MethodQuery methodQuery)

Returns a Function created from a method specified by a methodQuery. If the methodQuery matches none or more than one methods, a RuntimeException will be thrown.

To pass an input value given to an entry point method, such as TestAssertions.assertThat, to the method, use a place-holder value returned by parameter().

Type Parameters:

T - the type of the input to the returned function

Parameters:

methodQuery - A query object that specifies a method to be invoked by the returned function.

Returns:

Created function.

See Also:

classMethod(Class, String, Object[]), instanceMethod(Object, String, Object[]), parameter()

classMethod

public static MethodQuery classMethod(Class<?> targetClass,
                                      String methodName,
                                      Object... arguments)

Creates a MethodQuery object from given arguments to search for static methods. Note that arguments are actual argument values, not the formal parameter types. The pcond library searches for the "best" matching method for you. In case no matching method is found or more than one methods are found, a RuntimeException will be thrown.

In order to specify a parameter which should be passed to the returned function at applying, you can use an object returned by parameter() method. This is useful to construct a function from an existing method.

To pass an input value given to an entry point method, such as TestAssertions.assertThat, to the method, use a place-holder value returned by parameter().

That is, in order to create a function which computes sin using query a method Math.sin(double), you can do following

public class Example
  public void buildSinFunction() {
    MethodQuery mq = classMethod(Math.class, "sin", parameter());
    Function<Double, Double> sin = call(mq);
    System.out.println(sin(Math.PI/2));
  }
}

This prints 1.0.

In case your arguments do not contain any Parameter object, the input argument passed to the built function will be simply ignored.

Parameters:

targetClass - A class

methodName - A method name

arguments - Arguments

Returns:

A method query for static methods specified by arguments.

See Also:

ReflUtils.findMethod(Class, String, Object[]), parameter()

instanceMethod

public static MethodQuery instanceMethod(Object targetObject,
                                         String methodName,
                                         Object... arguments)

Creates a MethodQuery object from given arguments to search for static methods. Excepting that this method returns a query for instance methods, it is quite similar to classMethod(Class, String, Object[]).

This method is useful to build a function from an instance method. That is, you can create a function which returns the length of a given string from a method String.length() with a following code snippet.

public void buildLengthFunction() {
  Function<String, Integer> length = call(instanceMethod(parameter(), "length"));
}

In case the targetObject is not an instance of Parameter and arguments contain no Parameter object, the function will simply ignore the input passed to it.

To pass an input value given to an entry point method, such as TestAssertions.assertThat, to the method, use a place-holder value returned by parameter().

Parameters:

targetObject - An object on which methods matching returned query should be invoked.

methodName - A name of method.

arguments - Arguments passed to the method.

Returns:

A method query for instance methods specified by arguments.

See Also:

classMethod(Class, String, Object[]), parameter()

call

public static <T,R> Function<T,R> call(String methodName,
                                       Object... arguments)

Returns a function that calls a method which matches the given methodName and args on the object given as input to it.

Note that method look up is done when the predicate is applied. This means this method does not throw any exception by itself and in case you give wrong methodName or arguments, an exception will be thrown when the returned function is applied.

public class Example {
  public void method() {
    assertThat(value, transform(call("toString")).check(isNotNull()));
  }
}

To pass an input value given to an entry point method, such as TestAssertions.assertThat, to the method, use a place-holder value returned by parameter().

Type Parameters:

T - The type of input to the returned function

R - The type of output from the returned function

Parameters:

methodName - The method name

arguments - Arguments passed to the method.

Returns:

A function that invokes the method matching the methodName and args

See Also:

parameter()

expectingException

public static <T,E extends Throwable> Function<T,E> expectingException(Class<E> exceptionClass,
                                                                       Function<? super T,?> func)

Returns a function that converts an input value to an exception object, which is thrown by func, when it is applied. If it does not throw an exception, or even if thrown, it is not an instance of exceptionClass, an assertion executed inside this method will fail and an exception to indicate it will be thrown. The exception will be typically an AssertionError.

Type Parameters:

T - A type of exception value to be thrown by func.

E - An input value type of func.

Parameters:

exceptionClass - An exception class to be thrown.

func - A function to be exercised

Returns:

A function that maps an input value to an exception.

parameter

public static Parameter parameter()

Returns a Parameter object, which is used in combination with instanceMethod(Object, String, Object[]), classMethod(Class, String, Object[]), or their shorthand methods. The object returned by this method is replaced with the actual input value passed to a function built through call(MethodQuery) or Predicates.callp(MethodQuery) when it is applied.

Returns:

a Parameter object

See Also:

classMethod(Class, String, Object[]), instanceMethod(Object, String, Object[]), call(MethodQuery), call(String, Object[]), Predicates.callp(MethodQuery), Predicates.callp(String, Object[])

value

public static <E> E value()

A method to return a value for a "casting placeholder value".

Type Parameters:

E - Type to cast to.

Returns:

Casting placeholder value