Use Your Type System;Write Less Code

13th October 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

first second

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

return type Stream<Integer> Stream<PropertyId>

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”

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 fetchOne();}

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?

Readability

Searchability

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}

Searchability

Searchability

⇧F6

⌥⇧R

⌃R, ⌃R

F2

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

Searchability

Searchability

⌥F7

⌃G

⌃K, ⌃T

⇧⌥F7

public final class Templating { public void render(PropertyId propertyId) { propertyId.writeTo(output); } ...}

Searchability

Flexibility

public SearchQuery<PropertyId> searchForProperties( PurchasingType purchasingType, Budget budget, Area area) { Area rectangle = area.asRectangle(); return connection .query(“SELECT * FROM property” + “ WHERE purchasing_type = ?” + “ AND budget <= ?” + “ AND longitude BETWEEN ? AND ?” + “ AND latitude BETWEEN ? AND ?”, purchasingType.name(), budget.inGBP(), rectangle.minX(), rectangle.maxX(), rectangle.minY(), rectangle.maxY()) .filter(row -> area.contains(row.getDouble(“latitude”), row.getDouble(“longitude”))) .map(row -> new PropertyId(row.getInt(“id”)));}

Flexibility

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

Flexibility

Flexibility

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

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

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(select().from(“property”) .where(eq(“purchasing_type”, purchasingType.name())) .and(lte(“budget”, budget.inGBP())) .and(gte(“longitude”, rectangle.minX())) .and(lte(“longitude”, rectangle.maxX())) .and(gte(“latitude”, rectangle.minY())) .and(lte(“latitude”, rectangle.maxY()))) .filter(row -> area.contains(row.getDouble(“latitude”), row.getDouble(“longitude”))) .map(row -> new PropertyId( row.getUUID(“id”), row.getInt(“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) { if (distanceFromCentre <= 0) { throw new IllegalArgumentException( “The distance from centre must be positive.” + “ The value was ” + distanceFromCentre); } ...}

Correctness

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

Correctness

public final class Radius { public static Radius of( @NotNull double magnitude, @NotNull DistanceUnit unit) { check(“magnitude”, 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 fetchOne();}

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") 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

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

@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( id, formattedProperty(retrieveProperty(id))); } catch (DatabaseQueryException e) { return Response.serverError().entity(e).build(); } } private Response propertyResponse(PropertyId id, Output output) { if (output == null) { return Response.notFound().entity(id).build(); } return Response.ok(output).build(); } private Output formattedProperty(Property property) { if (property == null) { return null; } return PropertyTemplate.format(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 process( Function<Input, Output> processor, Input thing) { if (thing == null) { return null; } else { return processor.apply(thing); }}

Correctness

public final class Optional<T> { private final T value; public <U> Optional<U> map( Function<? super T, ? extends U> mapper) { if (value == null) { return empty(); } else { return Optional.ofNullable(mapper.apply(value)); } }}

Optional<Output> process( Function<Input, Output> processor, Optional<Input> thing) { return thing.map(processor);}

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).build()) .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

Efficiency

Efficiency

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

Set<ShortListedProperty> shortList = connection .query(“SELECT * FROM short_list” + “ JOIN property” + “ ON short_list.property_id = property.id” + “ WHERE short_list.user_id = ?”, user.id()) .map(row -> propertyFrom(row)) .fetch() .collect(toSet());

Efficiency

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

Efficiency

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

Efficiency

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

Efficiency

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

Efficiency

Stream<Property> randomPromotedAuction = connection .query(“SELECT * FROM property” + “ WHERE sale_type = ?” + “ AND promoted = true” + “ LIMIT 1”, PropertySaleType.AUCTION.name()) .fetch();List<Property> highlighted = Stream.concat(randomPromotedAuction, upForAuctionSoon.stream()) .collect(toList());

Efficiency

Efficiency

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; ...}

Efficiency

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; ...}

Efficiency

Efficiency

But we process the original 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; ...}

Efficiency

Efficiency

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; ...}

Efficiency

In Conclusion

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

Make a new type.

public class CircularArea implements Area { ...}

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

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.

13th October 2015@SamirTalwar