如何在Squeak FFI中同时支持32位与64位目标平台

Got it, let's break down how to get your Foo external structure working seamlessly on both 32-bit and 64-bit Squeak targets. The key is leveraging Squeak's built-in platform detection and FFI's flexible type system to generate the right field accessors automatically.

1. Implement the defineFields Method in Your Foo Class #

First, you'll need to override the defineFields class method to set up the struct fields in a platform-agnostic way. Squeak provides Smalltalk wordSize which returns 4 for 32-bit systems and 8 for 64-bit systems—perfect for adapting pointer sizes.

Here's the clean, straightforward code you can drop into your Foo class:

Foo class >> defineFields
	"Define struct fields that adapt to 32/64-bit pointer sizes"
	self resetFields. "Clear any existing field definitions first"
	
	"Add the float* data field: Squeak FFI automatically adapts pointer types to the platform's word size"
	self addField: #data type: 'float*'.
	
	"Add the size_t len field: FFI handles size_t's platform-dependent size natively"
	self addField: #len type: 'size_t'.
	
	"Generate getter/setter methods for the fields"
	self generateFieldAccessors

Alternative Explicit Pointer Size Approach #

If you prefer to be extra explicit about the pointer size (for clarity or edge cases), you can directly use Smalltalk wordSize to define the pointer field:

Foo class >> defineFields
	| pointerSize |
	pointerSize := Smalltalk wordSize. "4 for 32-bit, 8 for 64-bit"
	self resetFields.
	self addField: #data type: ('void*' size: pointerSize). "void* works here since we're storing a float pointer"
	self addField: #len type: 'size_t'.
	self generateFieldAccessors

Both approaches work—pick whichever makes your code more readable for your team.

2. Automate Field Generation on Package Load #

To ensure the field accessors are always generated correctly when your package loads (especially when switching platforms), you can hook this process into either the class's initialize method or your package's post-load script.

Option A: Use the Class Initialize Method #

Add this to your Foo class:

Foo class >> initialize
	self defineFields

Squeak will call this method automatically when the class is loaded, so the fields will be set up immediately without manual intervention.

Option B: Use a Package Post-Load Script #

If you're using Monticello for package management, open your package's definition, find the "Postload" section, and add:

Foo defineFields

This runs right after the package is loaded, guaranteeing the accessors are tailored to the current platform.

3. Verify Cross-Platform Compatibility #

To double-check everything works as expected, inspect the field offsets on both platforms:

• On 32-bit Squeak: Foo dataOffset should return 0, Foo lenOffset should return 4.
• On 64-bit Squeak: Foo dataOffset should return 0, Foo lenOffset should return 8.

You can also test creating an instance of Foo and setting/getting the fields to confirm no errors occur.

内容的提问来源于stack exchange，提问作者aka.nice