NAME

gen_bridge_metadata — Objective-C Bridges Metadata Generator

SYNOPSIS

DESCRIPTION

gen_bridge_metadata is a tool that generates bridging metadata information for a given framework or set of headers. The Objective-C bridges supported in Mac OS X, such as PyObjC (Python), read this information at runtime.

As of Mac OS 10.7, gen_bridge_metadata uses an improved parser, based on clang. This means the generated files should be more correct and complete, and the true parsing allows the automatic extraction of metadata from existing __attribute__() information supported by the compiler. File generation time should also be faster.

Metadata files describe the parts of an Objective-C framework that the bridges cannot automatically handle. These are primarily the ANSI C elements of the framework -- functions, constants, enumerations, and so on -- but also include special cases such as functions or methods that accept pointer-like arguments. These special cases must be manually specified in separate files called exceptions. The gen_bridge_metadata tool can then read in the exceptions file when it generates the framework metadata.

The file extension used for x86_64 metadata files should be .bridgesupport. The extension for arm64e metadata files should be .arm64e.bridgesupport.

Certain elements, such as inline functions, cannot be described in the metadata files. It is therefore required to generate a dynamic library in order to make the bridges use them. The gen_bridge_metadata tool can take care of that for you.

The file extension for the dynamic libraries should be .dylib.

You should install metadata files in one of three filesystem locations. For example, for a framework named MyFramework that is installed as /Library/Frameworks/MyFramework.framework, you can install the MyFramework.bridgesupport and MyFramework.dylib files in one of the following possible locations, in order of priority:

• /Library/Frameworks/MyFramework/Resources/BridgeSupport
• /Library/BridgeSupport
• ~/Library/BridgeSupport

OPTIONS

The gen_bridge_metadata tool accepts the following command-line options:

-f framework, --framework framework

Generates metadata for the given framework. This argument can accept both the name of a framework of an absolute path to a framework. When passing a framework name, the program will try to locate the framework in one of the standard framework locations.

-p, --private

Generates metadata based on the private headers of the given frameworks. This argument must be used with the -f argument.

-F format, --format format

Selects the metadata format that will be generated. Possible values are:

final

The final metadata format. This is the default value.

dylib

The dynamic library format. This is only required if you want to support inline functions. In order to use this format you need to pass a value for the -o argument.

exceptions-template

This will generate an exception template. Please consult BridgeSupport(5) for more details about the exception format. Once your exception file is finished you can pass it to the -e argument in order to generate the final metadata.

-e file, --exception file

Considers the given exception file when generating the final metadata format. The given exception file must conform to a certain format, described in bridgeSupport(5). Exception files are manually written, but you can generate a template by passing -F exceptions-template to the generator.

--arm64e

Write arm64e annotations instead of x86_64 and compiles the dylib as arm64e. If a dylib already exists at the output file path, a multi-architecture file will be created. An arm64e slice will be added to an x86_64 dylib. Conversely, if an arm64e dylib exists first, running the generator without the --arm64e argument will add an x86_64 slice.

--64-bit

This option has no effect. It is included for backwards compatibility, as 32-bit support is deprecated. Only 64-bit support exists.

--no-32-bit

This option has no effect. It is included for backwards compatibility, as 32-bit support is deprecated. Only 64-bit support exists.

--no-64-bit

This option has no effect. It is included for backwards compatibility, as 32-bit support is deprecated. Only 64-bit support exists.

-c, --cflags flags

Provides custom flags that will be passed to the C compiler. The generator compiles and executes several C and Objective-C programs during the generation of the final metadata format. Some flags are determined by default, but you might want to provide your own flags according to the piece of code you want to generate metadata for (for example, a framework part of a umbrella framework).

-C, --cflags-64 flags

Provides custom flags that will be passed to the C compiler, when generating 64-bit annotations. By default the same flags are passed to the C compiler when generating both 32-bit and 64-bit annotations.

-o, --output file

Writes the output to the given file. This argument is mandatory when generating the “dylib” format. For other formats, by default the output is redirected to the standard output.

-h, --help

Prints a summary of the options.

-d, --debug

Turns on debugging messages. You probably don't want to enable this option, unless you are going to debug the metadata generator.

-v, --version

Shows the version of the program. The version is also marked in generated metadata files, as the “version” attribute of the “signatures” top-level element.

EXAMPLES

This generates bridge support metadata for a custom framework:

If the custom framework has inline functions and you want to be able to call them, here is how you can generate a “dylib” file:

It is also possible to generate bridge support metadata for a standalone C library (here, libcurl):

SEE ALSO

BridgeSupport(5) /System/Library/DTDs/BridgeSupport.dtd ruby(1) python(1)