BridJAndScala

How to use BridJ from Scala

Introduction

BridJ was designed with JNAerator in mind, so that you never have to translate any C / C++ / ObjectiveC header by hand.

JNAerator creates Java sources or classes, that can then be used seamlessly from Scala.

However, BridJ has some Scala-specific features in its core classes, and JNAerator has Scala-specific generation modes.

This page details these Scala-oriented features.

Pointer

BridJ's pointer class was designed to behave like a list, so provided you import scala.collection.JavaConversions._ you'll be able to iterate over its pointed elements.

It also implements apply and update, so indexed access can be made with the natural Scala syntax :

val value = pointer(index)
pointer(index) = value

C code that demonstrates multi-dimensional arrays declarations and usage :

float array1d[100];
float array2d[100][200];
float array3d[100][200][300];

float v1 = array1d[10];
float v2 = array2d[10][20];
float v3 = array3d[10][20][30];
array3d[10][20][30] = v1 + v2 + v3;

Scala code :

import org.bridj.Pointer._

val array1d = allocateFloats(100)
val array2d = allocateFloats(100, 200)
val array3d = allocateFloats(100, 200, 300)

val v1 = array1d(10)
val v2 = array2d(10)(20)
val v3 = array3d(10)(20)(30)
array3d(10)(20)(30) = v1 + v2 + v3

Java code :

import org.bridj.Pointer;
import static org.bridj.Pointer.*;
...
Pointer<Float> 
	array1d = allocateFloats(100);
    
Pointer<Pointer<Float>> 
	array2d = allocateFloats(100, 200);

Pointer<Pointer<Pointer<Float>>> 
	array3d = allocateFloats(100, 200, 300);

float v1 = array1d.get(10);
float v2 = array2d.get(10).get(20);
float v3 = array3d.get(10).get(20).get(30);
array3d.get(10).get(20).set(30, v1 + v2 + v3);

Structs

When using JNAerator to create BridJ structs, you can use the -scalaSetters switch to generate setters in the form MyStruct.myField_= that are treated like setters by Scala.

These setters do not replace the usual generated setters, they're final and just call the usual setters.

C struct and code :

typedef struct S {
    int a;
    double d;
} S;

S s;
s.a = 10;
s.d = 10.0;

Scala code :

// Using autogenerated S structure code
val s = new S.a(10).d(10.0)

Scala code (using setters) :

val s = new S
s.a = 10
s.d = 10.0

Java code :

S s = new S().a(10).d(10.0)