Language Design Trade-offs

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Information about Language Design Trade-offs

Published on June 14, 2013

Author: abreslav



If your programming language is small, you’re probably born before 1950, and your first computer was bigger than your present apartment. And even those languages are not so small. One spends quite some time to master a programming language. Why?

Because there are very many decisions “compressed” into the form of a language. Nothing limits a programmer’s imagination like a compiler, and nothing limits a language design like a real world with all of its “legacy”, compatibility concerns, performance limitations, generations-old habits and leaky abstractions.

This talk is about tradeoffs: why we, as language designers, do (or rather did) this and not that.

LanguageDesignTrade-Offsandrey.breslav@ .comis

Simply Universal

Full of Shortcuts

Simply Universal

Full of Shortcuts

Trade-Off #0Elegance Convenience


Cool Practical

Clever ReadableSimple FastShiny New Good OldGround-Breaking Compatible

Shiny New Good Old

As Java Evolved…Foo<? extends T>new Foo()new Foo<T>()new Foo<>()SAM-ConversionsDefaultmethods

Lambdas & SAM-Conversionsvoid foo(Function<? super Bar, ? extends Baz> g)SAM-typefoo(g -> new SubBaz(g));

Compatibilityis a drag,son…

Simple Fast

Boxing for Primitivesnew Foo()The Age of (Auto)Boxing

LanguageRuntimeJITx86 amd64 ARMGCx86 amd64 ARMThreadsLinux Windows MacHardVeryHard

Ground-Breaking Compatible

JDK Collections interface List<E> {E get(int index);E set(int index, E value);}Read-only /** read-only */List<Foo> getFoos() {return unmodifiableList(l);}Errors At Runtime

Cool Collections interface List<E> {E get(int index);}interface MutableList<E>extends List<E> {E set(int index, E value);}Read-only List<Foo> getFoos() {return l; // may be mutable}Errors At Compile Time

Safe CompatibleCool Collections JDK Collectionscatch errors earlyself-documenting codeno wrapping/repackagingexisting API’s workIntuitive ? extends Fooprint(List<? extends Foo> foos)print(foos: List<Foo>)

Iterable<out T>Collection<out T>List<out T> Set<out T>MutableIterable<T>MutableCollection<T>MutableList<T> MutableSet<T>java.lang.ArrayList<T> java.util.HashSet<T>KotlinCollectionsJDKCollections

Kotlin Collections = &SafeCompatibleCo-variant

Java String s = null;s.length();Errors At RuntimeKotlin val s: Strings.length()val s: String? = nulls.length()Errors At Compile Time= nullNullabletype

Check and use val s: String? = …if (s != null) {s.length()}Check and exit if (s == null) returns.length()Rock’n’Roll s?.length()

JAR Fileclass Foo {String getName() { … }}Nullable or Not?<XML/>@NotNullKAnnotator

Dynamic Static

LibraryLocked*Util class

Util class Collections2.transform(Collections2.filter(list,(foo) -> foo.isValid()),(foo) -> new Bar(foo)));No Util Class scala.collection.Iterable[T]declares 116 methods

Ugly Interfaces Ugly Code

Java static char last(String s)Usage “abc”.last()C# static char last(string this)Kotlin fun String.last(): Char {return this[this.size - 1]}

Access privates NoVirtual NoOwner PackageMany Applicable Overloading errorMember Clashes Member wins= static utility

Theory Practice

Java new List<String>()Collections.<String>emptyList()Why different?Scala new List[String]()emptyList[String]()arr(0)Why square brackets?

foo(bar<A, B>(x + 1))foo(bar < a, b > (x + 1))

Java Familiar (from C++)Sometimes uglyScala Always prettyUnfamiliarC# andKotlinFamiliarAlways* prettyemptyList<String>()* foo((bar < A), B > (x+1))

Practiceis nicer thanTheory


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