Use Your Type System;Write Less Code

17th April 2015@SamirTalwar

So I’ve got this website.

It’s got a lot of code.

But a little while ago, I started to think it’s not as good as I thought when we were first getting started.

So I got to work.

Here’s what I found.

Readability

Readability

Tell me what’s more readable.

public Stream<Integer> searchForProperties( boolean renting, int monthlyBudget, double latitude, double longitude, double distanceFromCentre) { ... }

public Stream<PropertyId> abc( PurchasingType def, Budget ghi, Coordinate jkl, Radius mno) { ... }

Readability

Readability readable /ˈriːdəb(ə)l/ adjective

1. able to be read or deciphered; legible. “a code which is readable by a computer” synonyms: legible, easy to read, decipherable, easily deciphered, clear, intelligible, understandable, comprehensible, easy to understand “the inscription is still perfectly readable” antonyms: illegible, indecipherable 2. easy or enjoyable to read. “a marvellously readable book”

Readability readable /ˈriːdəb(ə)l/ adjective

1. able to be read or deciphered; legible. “a code which is readable by a computer” synonyms: legible, easy to read, decipherable, easily deciphered, clear, intelligible, understandable, comprehensible, easy to understand “the inscription is still perfectly readable” antonyms: illegible, indecipherable 2. easy or enjoyable to read. “a marvellously readable book”

first second

return type Stream<Integer> Stream<PropertyId>

name searchForProperties

buying or renting? boolean renting PurchasingType

monthly budget int monthlyBudget Budget

centre coordinates

double latitude,double longitude Coordinate

maximum distance

double distanceFromCentre Radius

Readability

Stream<Integer> searchResults = searchForProperties( true, 500, 51.525094, -0.127305, 2);

Stream<PropertyId> searchResults = searchForProperties( PropertyType.RENTAL, MonthlyBudget.of(500, GBP), Coordinate.of(51.525094, -0.127305), Radius.of(2, MILES));

Readability

Stream<PropertyId> searchResults = searchForProperties( PropertyType.RENTAL, MonthlyBudget.of(500, GBP), Coordinate.of(51.525094, -0.127305), Radius.of(2, MILES));

Stream<PropertyId> searchResults = searchForProperties( PropertyType.RENTAL, MonthlyBudget.of(500, GBP), CircularArea.around(Coordinate.of( 51.525094, -0.127305)) .with(Radius.of(2, MILES)));

Readability

Stream<PropertyId> searchForProperties( PurchasingType purchasingType, Budget budget, Area area) { ... }

SearchQuery<PropertyId> searchForProperties( PurchasingType purchasingType, Budget budget, Area area) { ... }

Readability

public interface SearchQuery<T> { public Stream<T> fetch(); public T fetchFirst();}

Readability

Readability

OK, the inputs make sense. But the output?

Why bother with a PropertyId?

public final class PropertyId { private final int value; public PropertyId(int value) { this.value = value; } public SearchQuery<Property> query( DatabaseConnection connection) { ... } public void renderTo(Somewhere else) { ... } // equals, hashCode and toString}

Readability

ReadabilityWhat does PropertyId do?

SearchQuery<Property> query (DatabaseConnection connection)

void renderTo(Somewhere else)

new PropertyId(int value)

String toString()

boolean equals(Object other) int hashCode()

Readabilityaddition

multiplication

subtraction

division

modulus

negation

bit manipulation operations such as &, |, ^ and ~

further bit manipulation functionality from java.lang.Integer (I count 9 separate methods)

equality

hashing

comparison with other integers

treatment as an unsigned integer

treatment as a sign (the Integer.signum function returns a value representing negative, positive or zero)

conversion to and from other number types (such as double)

conversion to and from strings in decimal, hexadecimal, octal and binary

all of the other methods on java.lang.Integer

What does int do?

Flexibility

public SearchQuery<PropertyId> searchForProperties( PurchasingType purchasingType, Budget budget, Area area) { Area rectangle = area.asRectangle(); return connection .query(query -> query .select() .from(PROPERTY) .where(PROPERTY.PURCHASING_TYPE.equal( purchasingType.name())) .and(PROPERTY.BUDGET.lessOrEqual(budget.inPounds())) .and(PROPERTY.LONGITUDE .between(rectangle.minX()).and(rectangle.maxX())) .and(PROPERTY.LATITUDE .between(rectangle.minY()).and(rectangle.maxY()))) .filter(row -> area.contains(row.getValue(PROPERTY.LATITUDE), row.getValue(PROPERTY.LONGITUDE))) .map(row -> new PropertyId(row.getValue(PROPERTY.ID)));}

Flexibility

public final class PropertyId { private final int value; ...}

Flexibility

Readability

But our website was slow, so we decided to switch to Cassandra.

public final class PropertyId { private final UUID value; private final int humanRepresentation; ...}

Flexibility

public SearchQuery<PropertyId> searchForProperties( PurchasingType purchasingType, Budget budget, Area area) { Area rectangle = area.asRectangle(); return connection .query(query -> query .select() .from(PROPERTY) .where(PROPERTY.PURCHASING_TYPE.equal( purchasingType.name())) .and(PROPERTY.BUDGET.lessOrEqual(budget.inPounds())) .and(PROPERTY.LONGITUDE .between(rectangle.minX()).and(rectangle.maxX())) .and(PROPERTY.LATITUDE .between(rectangle.minY()).and(rectangle.maxY()))) .filter(row -> area.contains(row.getValue(PROPERTY.LATITUDE), row.getValue(PROPERTY.LONGITUDE))) .map(row -> new PropertyId( row.getValue(PROPERTY.ID), row.getValue(PROPERTY.HUMAN_REPRESENTATION)));}

Flexibility

Correctness

Correctness

In his book, Understanding the Four Rules of Simple Design, Corey Haines talks about a really important concept in software design.

He calls things that embody this concept, behaviour attractors.

public Stream<Integer> searchForProperties( boolean renting, int monthlyBudget, double latitude, double longitude, double distanceFromCentre) { check(distanceFromCentre, is(greaterThan(0))); ...}

Correctness

public final class Radius { public static Radius of( @NotNull double magnitude, @NotNull DistanceUnit unit) { check(magnitude, is(greaterThan(0))); return new Radius(magnitude, unit); } private Radius( @NotNull double magnitude, @NotNull DistanceUnit unit) { ... } ...}

Correctness

Correctness

I haven’t been totally honest with you.

There’s more code than you thought.

Except it’s not really code.

/** * Searches for properties in the database * matching the specified parameters. * * @param renting True if renting, false if buying. * ... * @return A stream of property IDs. * @throws DatabaseQueryException if there is a connection error. */public Stream<Integer> searchForProperties( boolean renting, int monthlyBudget, double latitude, double longitude, double distanceFromCentre) { check(distanceFromCentre, is(greaterThan(0))); ...}

Correctness

/** * Searches for properties in the database * matching the specified parameters. * * @throws DatabaseQueryException * if there is a connection error. */Stream<PropertyId> searchForProperties( PurchasingType purchasingType, Budget budget, Area area) { ... }

Correctness

public interface SearchQuery<T> { /** * @throws DatabaseQueryException * if there is a connection error. */ public Stream<T> fetch(); /** * @throws DatabaseQueryException * if there is a connection error. */ public T fetchFirst();}

Correctness

public interface SearchQuery<T> { public Stream<T> fetch() throws DatabaseQueryException; public T fetchOne() throws DatabaseQueryException;}

Correctness

@Path("/properties")public final class PropertiesResource { private final Template PropertyTemplate = Template.inClassPath("/com/buymoarflats/website/property-details.html"); @GET @Path("/{propertyId}") public Response propertyDetails(@PathParam("propertyId") int id) { try { return propertyResponse(new PropertyId(id)); } catch (DatabaseQueryException e) { return Response.serverError().entity(e).build(); } } private Response propertyResponse(PropertyId id) throws DatabaseQueryException { Output output = formattedProperty(id); if (output == null) { return Response.notFound().entity(id).build(); } return Response.ok(output).build(); } private Output formattedProperty(PropertyId id) throws DatabaseQueryException { Property property = retrieveProperty(id); if (property == null) { return null; } return PropertyTemplate.format(property); } private Property retrieveProperty(PropertyId id) throws DatabaseQueryException { return id.query(connection).fetchOne(); }}

Correctness

public Response propertyDetails(@PathParam("propertyId") int id) { try { return propertyResponse(new PropertyId(id)); } catch (DatabaseQueryException e) { return Response.serverError().entity(e).build(); }}private Response propertyResponse(PropertyId id) throws DatabaseQueryException { Output output = formattedProperty(id); ... }private Output formattedProperty(PropertyId id) throws DatabaseQueryException { Property property = retrieveProperty(id); ... }private Property retrieveProperty(PropertyId id) throws DatabaseQueryException { return id.query(connection).fetchOne();}

Correctness

Correctness

To paraphrase Nat Pryce and Steve Freeman:

Your types are trying to tell you something.

You should listen to them.

public Response propertyDetails(@PathParam("propertyId") PropertyId id) { try { return propertyResponse( id, formattedProperty(retrieveProperty(id))); } catch (DatabaseQueryException e) { return Response.serverError().entity(e).build(); }}private Response propertyResponse(PropertyId id, Output output) { ...}private Output formattedProperty(Property property) { ...}private Property retrieveProperty(PropertyId id) throws DatabaseQueryException { return id.query(connection).fetchOne();}

Correctness

Correctness

Now, what about all that duplication?

Output process(Input thing) { if (thing == null) { return null; } // process thing and return}

Correctness

Output process(Input thing) { if (thing == null) { return null; } else { // process thing and return }}

Correctness

Output process(Input thing) { Function<Input, Output> processor = value -> { // process value and return }; if (thing == null) { return null; } else { return processor.apply(thing); }}

Correctness

Output processOptional( Function<Input, Output> processor, Input thing) { if (thing == null) { return null; } else { return processor.apply(thing); }}

Correctness

Optional<Output> process( Optional<Input> thing) { return thing.map(value -> { // process the thing and return });}

Correctness

public Response propertyDetails(@PathParam("propertyId") PropertyId id) { try { return propertyResponse( id, retrieveProperty(id).map(this::formattedProperty)); } catch (DatabaseQueryException e) { return Response.serverError().entity(e).build(); }}private Response propertyResponse(PropertyId id, Optional<Output> maybeOutput) { return maybeOutput .map(output -> Response.ok(output)) .orElse(Response.notFound().entity(id)) .build(); }private Output formattedProperty(Property property) { return PropertyTemplate.format(property); }

private Optional<Property> retrieveProperty(PropertyId id) throws DatabaseQueryException { return id.query(connection).fetchOne();}

Correctness

@GET@Path("/{propertyId}")public Response propertyDetails( @PathParam("propertyId") PropertyId id) { try { return id.query(connection).fetchOne() .map(PropertyTemplate::format) .map(Response::ok) .orElse(Response.notFound().entity(id)) .build(); } catch (DatabaseQueryException e) { return Response.serverError() .entity(e).build(); }}

Correctness

Correctness

That works with my DatabaseQueryException.

But what if my templating library can throw a TemplateFormattingException too?

public final class Optional<T> { ... public <U> Optional<U> map( Function<T, U> mapper) { ... }}

@FunctionalInterfacepublic interface Function<T, R> { R apply(T t); // does not throw ...}

Correctness

@GET@Path("/{propertyId}")public Response propertyDetails( @PathParam("propertyId") PropertyId id) { try { return id.query(connection).fetchOne() .map(PropertyTemplate::format) .map(Response::ok) .orElse(Response.notFound().entity(id)) .build(); } catch (DatabaseQueryException e) { return Response.serverError() .entity(e).build(); }}

Correctness

enum RequestFailure { ResourceNotFound, DatabaseQueryFailure, TemplateFormattingFailure}

Correctness

abstract class RequestException extends Exception { ... }final class ResourceNotFoundException extends RequestException { ... }final class DatabaseQueryException extends RequestException { ... }final class TemplateFormattingException extends RequestException { ... }

Correctness

Correctness

OK, I’ve got a type that can handle all of my failures.

But what about success?

Well, we can either have success or failure.

And if we fail, we don’t want to go any further.

public interface Either<F, S> { public <T> Either<F, T> then( Function<S, Either<F, T>> function);}

public class Failure<F, S> implements Either<F, S> { public <T> Either<F, T> then(Func<> function) { return new Failure<>(value); }}

public class Success<F, S> implements Either<F, S> { public <T> Either<F, T> then(Func<> function) { return function.apply(value); }}

Correctness

@Path("/properties")public final class PropertiesResource { @GET @Path("/{propertyId}") public Response propertyDetails( @PathParam("propertyId") PropertyId id) { Either<RequestException, Property> property = id.query(connection).fetchOne(); Either<RequestException, Output> output = property.then(PropertyTemplate::format); output .map(Response::ok) .on(ResourceNotFoundException.class, e -> Response.notFound().entity(id)) .failWith(e -> Response.serverError().entity(e)) .build(); }}

Correctness

@Path("/properties")public final class PropertiesResource { @GET @Path("/{propertyId}") public Response propertyDetails( @PathParam("propertyId") PropertyId id) { id.query(connection).fetchOne() .then(PropertyTemplate::format) .map(Response::ok) .on(ResourceNotFoundException.class, e -> notFound().entity(id)) .failWith(e -> serverError().entity(e)) .build(); }}

Correctness

Performance

Performance

On BuyMoarFlats.com, we let you short list properties.

Set<ShortListedProperty> shortList = connection .query(query -> query .select() .from(SHORT_LIST) .join(PROPERTY) .on(SHORT_LIST.PROPERTY_ID .eq(PROPERTY.ID)) .where(SHORT_LIST.USER_ID .eq(user.id()))) .map(row -> propertyFrom(row)) .fetch() .collect(toSet());

Performance

List<ShortListedProperty> sortedShortList = shortList.stream() .sorted(comparing(dateTimeAdded)) .collect(toList());

Performance

Map<City, List<ShortListedProperty>> shortListsByCity = sortedShortList.stream() .collect(groupingBy(city));

Performance

Set<City> cities = shortListByCity.keySet();

Performance

List<ShortListedProperty> upForAuctionSoon =shortListsByCity.values().stream() .flatMap(Collection::stream) .filter(property -> property.isUpForAuctionInLessThan( 1, WEEK)) .collect(toList());

Performance

Stream<Property> randomPromotedAuction = connection .query(query -> query .select() .from(PROPERTY) .where(PROPERTY.SALE_TYPE .eq(PropertySaleType.AUCTION)) .and(PROPERTY.PROMOTED.eq(true)) .limit(1)) .fetch();List<Property> highlighted = Stream.concat(randomPromotedAuction, upForAuctionSoon.stream()) .collect(toList());

Performance

Performance

And we’ve got more features coming every week!

public final class ShortList { Set<ShortListedProperty> shortList; List<ShortListedProperty> sortedShortList; Map<City, List<ShortListedProperty>> byCity; Set<City> cities; List<ShortListedProperty> upForAuctionSoon; Optional<Property> randomPromotedAuction; List<Property> highlighted; ...}

Performance

public final class ShortList { Set<ShortListedProperty> shortList; List<ShortListedProperty> sortedShortList; Map<City, List<ShortListedProperty>> byCity; Set<City> cities; List<ShortListedProperty> upForAuctionSoon; Optional<Property> randomPromotedAuction; List<Property> highlighted; ...}

Performance

Performance

But we process the list five times.

public final class ShortList { Set<ShortListedProperty> shortList; List<ShortListedProperty> sortedShortList; Map<City, List<ShortListedProperty>> byCity; Set<City> cities; List<ShortListedProperty> upForAuctionSoon; Optional<Property> randomPromotedAuction; List<Property> highlighted; ...}

Performance

Performance

Here’s the magic bullet.

We don’t need to optimise our algorithms.

The database author already did that.

We just need to write code that does less.

public final class ShortList { Map<City, List<ShortListedProperty>> byCity; Set<City> cities; List<Property> highlighted; ...}

Performance

In Conclusion

We tackled four discrete problems, but the solution was always the same.

Make a new type.

public class CircularArea implements Area { ...}

public final class Optional<T> { ...}

public final class Either<F, S> { ...}

Quoting @jbrains (who was paraphrasing Kent Beck),

“I define simple design this way.

A design is simple to the extent that it:

1. Passes its tests

2. Minimizes duplication

3. Maximizes clarity

4. Has fewer elements”

http://www.jbrains.ca/permalink/the-four-elements-of-simple-design

1. Passes its tests

2. Minimizes duplication

3. Maximizes clarity

4. Has fewer elements

Jackpot.

Go wrap some data in types.

talks.samirtalwar.com

Heckling starts now.

17th April 2015@SamirTalwar