Integration with Other Languages in Smalltalk

Smalltalk, known for its elegance and object-oriented purity, also excels in its ability to seamlessly integrate with other programming languages. This capability allows developers to

leverage existing libraries, harness performance optimizations, and extend the functionality of their Smalltalk applications beyond what is native to the language itself.

Understanding Integration

Integration with other languages in Smalltalk typically involves two primary approaches:

1. Foreign Function Interface (FFI):

Smalltalk environments often provide mechanisms to call functions written in other languages such as C, C++, or even assembly language. This is facilitated through a Foreign Function Interface, which acts as a bridge between Smalltalk and the target language. Developers can declare external functions and data structures in Smalltalk, specifying their signatures and any necessary conversions between data types. This allows Smalltalk programs to invoke functions implemented in the target language directly.

2. Interoperability Frameworks:

Beyond simple FFI, some Smalltalk dialects offer sophisticated interoperability frameworks. These frameworks enable deeper integration by allowing objects from other languages to be instantiated within Smalltalk, and vice versa. They manage memory allocation, data conversion, and method invocation between the languages, providing a more seamless experience for developers aiming to combine the strengths of multiple languages in a single application.

Implementation Example

Certainly! Let’s clarify with a simple example to demonstrate how Smalltalk can integrate with C/C++ using a Foreign Function Interface (FFI). In Smalltalk, the FFI allows you to call functions written in C or C++ directly from your Smalltalk code. This is particularly useful when you need to perform computationally intensive tasks or interact with system-level functions efficiently.

Example Scenario

Let’s consider a scenario where you have a Smalltalk application that needs to calculate the sum of an array of integers. While Smalltalk can handle this task, we’ll use C++ through FFI for demonstration purposes.

Step 1: Define the C++ Function

First, you write a simple C++ function that calculates the sum of an array of integers. Save this in a file named `sum.cpp`:

// sum.cpp
#include <iostream>

extern "C" {
    int sum(int* array, int size) {
        int result = 0;
        for (int i = 0; i < size; ++i) {
            result += array[i];
        }
        return result;
    }
}

In this C++ code:

• The ‘sum‘ function takes an array of integers (‘array‘) and its size (‘size‘).
• It iterates through the array, accumulating the sum of its elements.
• The `extern "C"` ensures that the function uses C-linkage, which is necessary for FFI in many Smalltalk implementations.

Step 2: Compile the C++ Code

Compile `sum.cpp` into a shared library. Here’s how you can do it on a Unix-like system (like Linux):

g++ -shared -o libsum.so sum.cpp

This command compiles ‘sum.cpp‘ into a shared library ‘libsum.so‘, which Smalltalk can dynamically load and use.

Step 3: Smalltalk Code to Use the C++ Function

Now, let’s write Smalltalk code that calls the ‘sum‘ function from the compiled shared library (‘libsum.so‘).

"Assuming we're using Pharo Smalltalk"

| libHandle sumFunction |

"Load the shared library"
libHandle := SmalltalkFFI libraryNamed: 'libsum.so'.

"Define the function signature in Smalltalk"
sumFunction := (CFunctionPointer
    newIn: libHandle
    functionName: 'sum'
    module: nil
    ffiType: #(int (int* int))
).

"Call the C++ function from Smalltalk"
| array size result |
array := #(1 2 3 4 5).
size := array size.
result := sumFunction callWith: { array asByteArray startingAt: 1. } value: size.

Transcript show: 'Sum of the array: ', result printString; cr.

Explanation

Loading the Library (`libsum.so`):

• `libHandle := SmalltalkFFI libraryNamed: 'libsum.so'.: This line loads the compiled shared library 'libsum.so‘ into Smalltalk.

Defining the Function Signature:

• `sumFunction := (CFunctionPointer newIn: libHandle functionName: 'sum' module: nil ffiType: #(int (int* int)) ).` : Here, we define the function sum from libsum.so. ffiType: #(int (int* int)) specifies that sum returns an int and takes an int* (pointer to int) and an int (size) as arguments.

Calling the C++ Function from Smalltalk:

• result := sumFunction callWith: { array asByteArray startingAt: 1. } value: size.: This line calls the ‘sum‘ function defined in C++ with ‘array‘ (converted to a byte array) and ‘size‘ as arguments.

Benefits of Integration

1. Reuse of Existing Code:

• Integration enables Smalltalk developers to reuse existing libraries and components written in other languages without needing to reimplement them from scratch.
• This enhances productivity and reduces development time, as developers can leverage tested and optimized code that already exists.

2. Performance Optimization:

• By integrating with languages like C or C++, developers can optimize performance-critical sections of their applications.
• Operations that require low-level manipulation or efficient memory handling can be implemented in a language that provides greater control over these aspects.

3. Extending Functionality:

• Smalltalk’s integration capabilities allow developers to extend the functionality of their applications beyond what is readily available in Smalltalk alone.
• Complex algorithms, hardware interaction, or system-level tasks can be implemented using languages better suited to these domains, while still integrating seamlessly with the Smalltalk application.