Functions.java

/*
 * Copyright (c) 2002-2015 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.neo4j.function;

import java.util.Map;

/**
 * Constructors for basic {@link Function} and {@link BiFunction} types
 */
public final class Functions
{
    public static <From, To> Function<From,To> map( final Map<From,To> map )
    {
        return new Function<From,To>()
        {
            @Override
            public To apply( From from )
            {
                return map.get( from );
            }
        };
    }

    public static <From, To> Function<From,To> withDefaults( final Function<From,To> defaults, final Function<From,
            To> f )
    {
        return new Function<From,To>()
        {
            @Override
            public To apply( From from )
            {
                To to = f.apply( from );

                if ( to == null )
                {
                    return defaults.apply( from );
                }
                else
                {
                    return to;
                }
            }
        };
    }

    public static <From, To> Function<From,To> nullFunction()
    {
        return new Function<From,To>()
        {
            @Override
            public To apply( From from )
            {
                return null; // Always return null
            }
        };
    }

    public static <From, To> Function<From,To> constant( final To value )
    {
        return new Function<From,To>()
        {
            @Override
            public To apply( From from )
            {
                return value;
            }
        };
    }

    private static UnaryOperator IDENTITY = new UnaryOperator()
    {
        @Override
        public Object apply( Object value )
        {
            return value;
        }
    };

    @SuppressWarnings( "unchecked" )
    public static <T> UnaryOperator<T> identity()
    {
        return IDENTITY;
    }

    public static <From, From2, To> Function2<? super Function<From,From2>,? super Function<From2,To>,Function<From,To>> compose()
    {
        return new Function2<Function<From,From2>,Function<From2,To>,Function<From,To>>()
        {
            @Override
            public Function<From,To> apply( final Function<From,From2> f1, final Function<From2,To> f2 )
            {
                return new Function<From,To>()
                {
                    @Override
                    public To apply( From from )
                    {
                        return f2.apply( f1.apply( from ) );
                    }
                };
            }
        };
    }

    public static <T1, T2> Function2<? super BiFunction<T1,T2,T1>,? super BiFunction<T1,T2,T1>,Function2<T1,T2,T1>> compose2()
    {
        return new Function2<BiFunction<T1,T2,T1>,BiFunction<T1,T2,T1>,Function2<T1,T2,T1>>()
        {
            @Override
            public Function2<T1,T2,T1> apply( final BiFunction<T1,T2,T1> function1, final BiFunction<T1,T2,
                    T1> function2 )
            {
                return new Function2<T1,T2,T1>()
                {
                    @Override
                    public T1 apply( T1 from1, T2 from2 )
                    {
                        return function1.apply( function2.apply( from1, from2 ), from2 );
                    }
                };
            }
        };
    }

    public static Function<Object,String> TO_STRING = new Function<Object,String>()
    {
        @Override
        public String apply( Object from )
        {
            if ( from != null )
            {
                return from.toString();
            }
            else
            {
                return "";
            }
        }
    };

    public static <FROM, TO> Function<FROM,TO> cast( final Class<TO> to )
    {
        return new Function<FROM,TO>()
        {
            @Override
            public TO apply( FROM from )
            {
                return to.cast( from );
            }

            @Override
            public String toString()
            {
                return "cast(to=" + to.getName() + ")";
            }
        };
    }

    public static <T> Function<T,Void> fromConsumer( final Consumer<T> consumer )
    {
        return new Function<T,Void>()
        {
            @Override
            public Void apply( T t )
            {
                consumer.accept( t );
                return null;
            }
        };
    }

    public static <T> Function<Void,T> fromSupplier( final Supplier<T> supplier )
    {
        return new Function<Void,T>()
        {
            @Override
            public T apply( Void t )
            {
                return supplier.get();
            }
        };
    }

    /**
     * @deprecated use {@link Consumers#noop()}
     */
    @Deprecated
    @SuppressWarnings( "unchecked" )
    public static <TYPE> Consumer<TYPE> swallow( @SuppressWarnings( "UnusedParameters" ) Class<TYPE> type )
    {
        return Consumers.noop();
    }

    /**
     * @deprecated use {@link Suppliers#singleton(Object)}
     */
    @Deprecated
    public static <T> Factory<T> constantly( final T item )
    {
        return new Factory<T>()
        {
            @Override
            public T newInstance()
            {
                return item;
            }
        };
    }
}