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### `load_library( $path_or_name )`

Locates and loads a dynamic library into memory, returning an opaque `Affix::Lib` handle.

```perl
my $lib = load_library('sqlite3');
```

**Lifecycle:** Library handles are thread-safe and internally reference-counted. The underlying OS library is only
closed (e.g., via `dlclose` or `FreeLibrary`) when all Affix wrappers and pins relying on it are destroyed.

_Note:_ When using `affix()` or `wrap()`, you can safely pass the string name directly (e.g., `affix('sqlite3',
...)`) and Affix will call `load_library` for you internally. If you pass `undef` instead of a library name, Affix
will search the currently running executable process.

### `locate_lib( $name, [$version] )`

Searches for a library using Affix's discovery engine and returns its absolute file path as a string. It **does not**
load the library into memory. This is useful if you need to pass the library path to another tool or check for its
existence.

```perl
# Find libssl.so.1.1 or libssl.1.1.dylib
my $path = locate_lib('ssl', '1.1');
say "Found SSL at: $path" if $path;
```

### `find_symbol( $lib_handle, $symbol_name )`

Looks up an exported symbol (function or global variable) inside an already-loaded `Affix::Lib` handle. Returns an
unmanaged `Affix::Pointer` (Pin) of type `Pointer[Void]` pointing to the memory address of the symbol.

```perl
my $lib = load_library('m');

# Get the raw memory address of the 'pow' function
my $pow_ptr = find_symbol($lib, 'pow');

if ($pow_ptr) {
    say sprintf("pow() is located at: 0x%X", address($pow_ptr));
}
```

Returns `undef` if the symbol cannot be found.

### `libc()` and `libm()`

Helper functions that locate and return the file paths to the standard C library and the standard math library for the
current platform. Because platform implementations differ wildly (e.g., MSVCRT on Windows, glibc on Linux, libSystem on
macOS), using these helpers guarantees you get the correct library.

```perl
# Bind 'puts' from the standard C library
affix libc(), 'puts', [String] => Int;

# Bind 'cos' from the math library
affix libm(), 'cos', [Double] => Double;
```

### `get_last_error_message()`

If `load_library`, `find_symbol`, or a signature parsing step fails, this function returns a string describing the
most recent internal or operating system error (via `dlerror` or `FormatMessage`).

```perl
my $lib = load_library('does_not_exist');
if (!$lib) {
    die "Failed to load library: " . get_last_error_message();
}
```

# INTROSPECTION

When working with C APIs, you often need to know exactly how much memory a structure consumes or where a specific field
is located within a block of memory. Affix provides compiler-grade type introspection.

### `sizeof( $type )`

Returns the size, in bytes, of any Affix Type object or registered `typedef` name.

```
# C: sizeof(int);
say sizeof( Int ); # 4 (usually)

# C: sizeof(Point);
say sizeof( Point() ); # 8
```

### `alignof( $type )`

Returns the alignment boundary (in bytes) required by the C ABI for the given type.

```perl
say alignof( Int64 ); # 8 (usually)

# Struct alignment is dictated by its largest member
typedef Mixed => Struct[ a => Char, b => Double ];
say alignof( Mixed() ); # 8
```

### `offsetof( $struct_or_union, $field_name )`

Returns the byte offset of a named field within an Aggregate type (Struct or Union). This is incredibly useful for
manual pointer arithmetic.

```perl
typedef Rect => Struct[ x => Int, y => Int, w => Int, h => Int ];

# C: offsetof(Rect, w);
say offsetof( Rect(), 'w' ); # 8 (skips x and y, 4 bytes each)
```

### `types()`

Returns a list of all custom type names currently registered in Affix's global type registry via `typedef`. In scalar
context, returns the total number of registered types.

```perl
my @known_types = types();
say "Registered types: " . join(', ', @known_types);
```

# INTERFACING WITH OTHER LANGUAGES

Because Affix dynamically loads symbols according to the C Application Binary Interface (C ABI), it can interact with
libraries written in almost any language, provided they expose their functions correctly. Companion modules like
[Affix::Build](https://metacpan.org/pod/Affix%3A%3ABuild) make compiling these languages seamless.

README.md  view on Meta::CPAN

## C++

C++ uses "name mangling" to support function overloading and namespaces, which alters the final symbol name inside the
compiled library.

- 1. **Prevent Mangling:** Wrap your exported functions in `extern "C"` to ensure they have predictable names.

    ```
    extern "C" {
        int add(int a, int b) { return a + b; }
    }
    ```

- 2. **Or Use Mangled Names:** If you cannot change the C++ source, you must look up the exact mangled name (e.g., `_Z3addii`) using tools like `nm` or `objdump`, and bind to that.
- 3. **Object Methods:** Calling an object's method requires passing the object instance pointer (the `this` pointer) as the first argument. Use the `ThisCall( ... )` wrapper around your callback/signature to automatically insert `Pointer[Void]` at t...

## Rust

Rust does not use the C ABI by default. You must explicitly instruct the compiler to format the function correctly.

- 1. **Exporting:** Use `#[no_mangle]` and `pub extern "C"`.

    ```rust
    #[no_mangle]
    pub extern "C" fn add(a: i32, b: i32) -> i32 { a + b }
    ```

- 2. **Structs:** Rust structs must be annotated with `#[repr(C)]` to guarantee their memory layout matches C (and thus Affix's `Struct`).
- 3. **Strings:** Rust strings are not null-terminated. You must receive `String` arguments as `*const std::os::raw::c_char` and convert them using `CStr::from_ptr`.

## Fortran

Fortran relies heavily on pass-by-reference.

- 1. **Pointers Everywhere:** Unless a parameter uses the modern Fortran `VALUE` attribute, you must pass everything as a pointer. If the function expects a Float, your Affix signature must be `Pointer[Float]`.
- 2. **Name Mangling:** Most Fortran compilers convert subroutine names to lowercase and append an underscore. A Fortran subroutine named `CALC_STRESS` will likely be exported as `calc_stress_`.
- 3. **Strings:** Fortran does not use null-terminated strings. When passing character arrays, Fortran compilers silently append hidden "length" parameters at the **end** of the argument list (passed by value as integers).

## Assembly

When writing raw Assembly (NASM/GAS), you must manually adhere to the calling convention of your target platform:

- **Linux/macOS (System V AMD64 ABI):** Arguments are passed in `rdi, rsi, rdx, rcx, r8, r9`, with the rest on the stack.
- **Windows (Microsoft x64):** Arguments are passed in `rcx, rdx, r8, r9`, with "shadow space" reserved on the stack.

## Go

Go libraries can be loaded if they are compiled with `-buildmode=c-shared`. Note that Go slices and strings contain
internal metadata (length/capacity) and do not map directly to C arrays or `char*`. Use the `C` package inside Go
(`import "C"`) and `*C.char` to bridge the boundary.

# ERROR HANDLING & DEBUGGING

Bridging two entirely different runtimes can lead to spectacular crashes if types or memory boundaries are mismatched.
Affix provides built-in tools to help you identify what went wrong.

## Error Handling

### `errno()`

Accesses the system error code from the most recent FFI or standard library call (reads `errno` on Unix and
`GetLastError` on Windows).

This function returns a **dualvar**. It behaves as an integer in numeric context, and magically resolves to the
human-readable system error message (via `strerror` or `FormatMessage`) in string context.

```perl
# Suppose a C file-open function fails
my $fd = c_open("/does/not/exist");
if (!$fd) {
    my $err = errno();

    # String context
    say "Failed to open: $err"; # "No such file or directory"

    # Numeric context
    if (int($err) == 2) {
        say "Code 2 specifically triggered.";
    }
}
```

**Note:** You must call `errno()` immediately after the C function invokes, as subsequent Perl operations (like
printing to STDOUT) might overwrite the system's error register.

## Memory Inspection

### `dump( $pin, $length_in_bytes )`

Prints a formatted hex dump of the memory pointed to by a Pin directly to `STDOUT`. This is an invaluable tool for
verifying that C structs or buffers contain the data you expect.

```perl
my $ptr = strdup("Affix Debugging");
dump($ptr, 16);

# Output:
# Dumping 16 bytes from 0x55E9A8A5 at script.pl line 42
#  000  41 66 66 69 78 20 44 65 62 75 67 67 69 6e 67 00 | Affix Debugging.
```

### `sv_dump( $scalar )`

Dumps Perl's internal interpreter structure (SV) for a given scalar to `STDOUT`. This exposes the raw flags, reference
counts, and memory layout of the Perl variable itself.

```perl
my $val = 42;
sv_dump($val);
# Exposes IV flags, memory addresses of the SV head, etc.
```

## Advanced Debugging

### `set_destruct_level( $level )`

Sets the internal `PL_perl_destruct_level` variable.

When testing XS/FFI code for memory leaks using tools like Valgrind or AddressSanitizer, you often want Perl to
meticulously clean up all global memory during its destruction phase (otherwise the leak checker will be flooded with
false-positive "leaks" that are actually just memory Perl intentionally leaves to the OS to reclaim).

```
# Call this at the start of your script when running under Valgrind
set_destruct_level(2);
```

# COMPANION MODULES

Affix ships with two powerful companion modules to streamline your FFI development:

- [**Affix::Wrap**](https://metacpan.org/pod/Affix%3A%3AWrap): Parses C/C++ headers using the Clang AST to automatically generate Affix bindings for entire libraries.
- [**Affix::Build**](https://metacpan.org/pod/Affix%3A%3ABuild): A polyglot builder that compiles inline C, C++, Rust, Zig, Go, and 15+ other languages into dynamic libraries you can bind instantly.

# THREAD SAFETY & CONCURRENCY

Affix bridges Perl (a single-threaded interpreter, generally) with libraries that may be multi-threaded. This creates
potential hazards that you must manage.

## 1. Initialization Phase vs. Execution Phase

Functions that modify Affix's global state are **not thread-safe**. You must perform all definitions in the main thread
before starting any background threads or loops in the library.