io.vavr.CheckedFunction0 Maven / Gradle / Ivy
/* __ __ __ __ __ ___
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* \____/__/ \__\____/__/
*
* Copyright 2014-2020 Vavr, http://vavr.io
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package io.vavr;
/*-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-*\
G E N E R A T O R C R A F T E D
\*-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-*/
import static io.vavr.CheckedFunction0Module.sneakyThrow;
import io.vavr.control.Option;
import io.vavr.control.Try;
import java.io.Serializable;
import java.util.Objects;
import java.util.function.Function;
import java.util.function.Supplier;
/**
* Represents a function with no arguments.
*
* @param return type of the function
* @author Daniel Dietrich
*/
@FunctionalInterface
public interface CheckedFunction0 extends Serializable {
/**
* The serial version uid.
*/
long serialVersionUID = 1L;
/**
* Returns a function that always returns the constant
* value that you give in parameter.
*
* @param the result type
* @param value the value to be returned
* @return a function always returning the given value
*/
static CheckedFunction0 constant(R value) {
return () -> value;
}
/**
* Creates a {@code CheckedFunction0} based on
*
*
* Examples (w.l.o.g. referring to Function1):
* // using a lambda expression
* Function1<Integer, Integer> add1 = Function1.of(i -> i + 1);
*
* // using a method reference (, e.g. Integer method(Integer i) { return i + 1; })
* Function1<Integer, Integer> add2 = Function1.of(this::method);
*
* // using a lambda reference
* Function1<Integer, Integer> add3 = Function1.of(add1::apply);
*
*
* Caution: Reflection loses type information of lambda references.
*
// type of a lambda expression
* Type<?, ?> type1 = add1.getType(); // (Integer) -> Integer
*
* // type of a method reference
* Type<?, ?> type2 = add2.getType(); // (Integer) -> Integer
*
* // type of a lambda reference
* Type<?, ?> type3 = add3.getType(); // (Object) -> Object
*
*
* @param methodReference (typically) a method reference, e.g. {@code Type::method}
* @param return type
* @return a {@code CheckedFunction0}
*/
static CheckedFunction0 of(CheckedFunction0 methodReference) {
return methodReference;
}
/**
* Lifts the given {@code partialFunction} into a total function that returns an {@code Option} result.
*
* @param partialFunction a function that is not defined for all values of the domain (e.g. by throwing)
* @param return type
* @return a function that applies arguments to the given {@code partialFunction} and returns {@code Some(result)}
* if the function is defined for the given arguments, and {@code None} otherwise.
*/
@SuppressWarnings("RedundantTypeArguments")
static Function0> lift(CheckedFunction0 partialFunction) {
return () -> Try.of(partialFunction::apply).toOption();
}
/**
* Lifts the given {@code partialFunction} into a total function that returns an {@code Try} result.
*
* @param partialFunction a function that is not defined for all values of the domain (e.g. by throwing)
* @param return type
* @return a function that applies arguments to the given {@code partialFunction} and returns {@code Success(result)}
* if the function is defined for the given arguments, and {@code Failure(throwable)} otherwise.
*/
static Function0> liftTry(CheckedFunction0 partialFunction) {
return () -> Try.of(partialFunction::apply);
}
/**
* Narrows the given {@code CheckedFunction0} to {@code CheckedFunction0}
*
* @param f A {@code CheckedFunction0}
* @param return type
* @return the given {@code f} instance as narrowed type {@code CheckedFunction0}
*/
@SuppressWarnings("unchecked")
static CheckedFunction0 narrow(CheckedFunction0 f) {
return (CheckedFunction0) f;
}
/**
* Applies this function to no arguments and returns the result.
*
* @return the result of function application
* @throws Throwable if something goes wrong applying this function to the given arguments
*/
R apply() throws Throwable;
/**
* Returns the number of function arguments.
* @return an int value >= 0
* @see Arity
*/
default int arity() {
return 0;
}
/**
* Returns a curried version of this function.
*
* @return a curried function equivalent to this.
*/
default CheckedFunction0 curried() {
return this;
}
/**
* Returns a tupled version of this function.
*
* @return a tupled function equivalent to this.
*/
default CheckedFunction1 tupled() {
return t -> apply();
}
/**
* Returns a reversed version of this function. This may be useful in a recursive context.
*
* @return a reversed function equivalent to this.
*/
default CheckedFunction0 reversed() {
return this;
}
/**
* Returns a memoizing version of this function, which computes the return value for given arguments only one time.
* On subsequent calls given the same arguments the memoized value is returned.
*
* Please note that memoizing functions do not permit {@code null} as single argument or return value.
*
* @return a memoizing function equivalent to this.
*/
default CheckedFunction0 memoized() {
if (isMemoized()) {
return this;
} else {
final Lazy lazy = Lazy.of(() -> {
try {
return apply();
} catch (Throwable x) {
throw new RuntimeException(x);
}
});
return (CheckedFunction0 & Memoized) () -> {
try {
return lazy.get();
} catch(RuntimeException x) {
throw x.getCause();
}
};
}
}
/**
* Checks if this function is memoizing (= caching) computed values.
*
* @return true, if this function is memoizing, false otherwise
*/
default boolean isMemoized() {
return this instanceof Memoized;
}
/**
* Return a composed function that first applies this CheckedFunction0 to the given arguments and in case of throwable
* try to get value from {@code recover} function with same arguments and throwable information.
*
* @param recover the function applied in case of throwable
* @return a function composed of this and recover
* @throws NullPointerException if recover is null
*/
default Function0 recover(Function> recover) {
Objects.requireNonNull(recover, "recover is null");
return () -> {
try {
return this.apply();
} catch (Throwable throwable) {
final Supplier func = recover.apply(throwable);
Objects.requireNonNull(func, () -> "recover return null for " + throwable.getClass() + ": " + throwable.getMessage());
return func.get();
}
};
}
/**
* Returns an unchecked function that will sneaky throw if an exceptions occurs when applying the function.
*
* @return a new Function0 that throws a {@code Throwable}.
*/
default Function0 unchecked() {
return () -> {
try {
return apply();
} catch(Throwable t) {
return sneakyThrow(t);
}
};
}
/**
* Returns a composed function that first applies this CheckedFunction0 to the given argument and then applies
* {@linkplain CheckedFunction1} {@code after} to the result.
*
* @param return type of after
* @param after the function applied after this
* @return a function composed of this and after
* @throws NullPointerException if after is null
*/
default CheckedFunction0 andThen(CheckedFunction1 after) {
Objects.requireNonNull(after, "after is null");
return () -> after.apply(apply());
}
}
interface CheckedFunction0Module {
// DEV-NOTE: we do not plan to expose this as public API
@SuppressWarnings("unchecked")
static R sneakyThrow(Throwable t) throws T {
throw (T) t;
}
}