Project Lambda - Closures after all?

Project Lambda or #()(”Project Lambda”) 2010-04-29

Lambda Expressions (aka Closures)
“ a first-class function with free variables that are bound in the lexical environment” - Wikipedia
HUGE debate about various closures decision earlier BGGA, CICE, FCM, …
Oracle seems to have decided this without JSR/JCP - most likely that this will be included in Java 7
Straw-Man Proposol - first-class functions - function types - lambda expression
Syntax and content not definite, may change
Complexity budget reached?

Lambda Expressions – Suggested Syntax
A new way of writing anonymous functions
A functions which take an int and returns its double
#() (42) //no args, returns 42 #(int x) (x+x)

Lambda Expressions
Complex expressions
#(int x, int y){ int z = expensiveComputation(x, y); if (z < 0) return x; if (z > 0) return y; return 0; }

Function Types
Every expression in Java must have a type, i.e. introduce function types
… and they could be invoked
#int() fortyTwo = #()(42); #int(int) doubler = #(int x)(x + x); assert fortyTwo() == 42; assert doubler(fortyTwo()) == 84;

Functions as arguments
Methods can take a function as an argument
public int[] map(int[] a, #int(int) fn) { int[] b = new int[a.length]; for (int i = 0; i < a.length; i++) b[i] = fn(a[i]); return b; }

SAM types
Interfaces with just one method (SAM)
Thread th = new Thread(new Runnable() { public void run() { doSomeStuff(); doMoreStuff(); } }); Thread th = new Thread(#(){ doSomeStuff(); doMoreStuff(); } )

Variable Capture shared int count = 0; Collections.sort(data, #(String a, String b){ count++; return a.length() - b.length()}); System.out.println(count);

Project Lambda - Closures after all?

by Andreas Enbohm on Jun 24, 2010

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Project Lambda - Closures after all? — Presentation Transcript