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Exploring Clang Modules
Samuel Giddins
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@segiddins
CocoaPods, Bundler, RubyGems
Mobile Developer Experience @ Square
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cool_function.h
#define AUTHORS_NAME "segiddins"
extern void printMyName(char *);
main.c
#include "cool_function.h"
int main(int argc, char **argv) {
printMyName(AUTHORS_NAME);
}
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main.c
extern void printMyName(char *);
int main(int argc, char **argv) {
printMyName("segiddins");
}
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#include "header.h"
#define MAGIC_NUMBER 42
...
...
...
#include "header2.h" // also includes header.h
preprocessed into:
static int secretNumber = -1;
static int secretNumber = 42;
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// header.h
#ifndef __HEADER_H
#define __HEADER_H
...
#endif // #ifndef __HEADER_H
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#import "header.h"
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Enter Module Maps
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UsefulFramework.modulemap / module.modulemap
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
export *
module * { export * }
}
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UsefulFramework.modulemap
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
export *
module * { export * }
}
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UsefulFramework.modulemap
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
export *
module * { export * }
}
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UsefulFramework.modulemap
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
export *
module * { export * }
}
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UsefulFramework.modulemap
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
export *
module * { export * }
}
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main.swift
import UsefulFramework
main.m
@import UsefulFramework;
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Module Maps, the hard part
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Module Maps, the hard part
Lessons from CocoaPods
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• Umbrella Directories
• Explicit Submodules
• Private Headers
• Textual Headers
• ...
• Automatic Module Map Discovery
• Relative Paths
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Umbrella Directories
framework module UsefulFramework {
umbrella "HeadersDirectory"
}
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Explicit Submodules
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Explicit Submodules
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
explicit module ForSubclassEyesOnly {
header "ComplicatedTextField_subclass.h"
}
}
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Private Headers
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
private header "PrivateHashMapImpl.h"
}
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Textual Headers
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
textual header "AssertMacros.h"
}
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Requires
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
requires objc_arc, blocks, !altivec
}
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Conflicts
framework module UsefulFramework {
umbrella header "UsefulFramework.h"
conflict PointlessFramework, "we do something more useful than that framework"
}
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Automatic Module Map Discovery
$ tree include
include
!"" baking.h
!"" cake.h
!"" cookie.h
!"" module.modulemap
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Relative Paths
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Relative Paths
framework module UsefulFramework {
header "UsefulFramework.h"
}
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Modules & Swift
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But my Swift code doesn't have headers...
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But my Swift code doesn't have headers...
It does
!
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swiftc Understands .swiftmodule Files
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The Mixed Framework Process
1. Compile all .swift files
2. Generate ModuleName-Swift.h in the (empty) .framework
3. "Extend" existing module map with .Swift submodule
4. Compile .m files
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Extended Module Maps
module ModuleName.Swift {
header "ModuleName-Swift.h"
requires objc
}
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Same-Module Imports
Superclass.m
#import
Subclass.swift
// nothing to import!
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Same-Module Imports
swiftc Useful.swift
-module-name UsefulFramework
-import-underlying-module
-emit-module
-emit-objc-header
-Xcc -fmodule-map-file="UsefulFramework.modulemap"
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Swift Static Libraries in CocoaPods
All of the changes needed:
https://github.com/CocoaPods/CocoaPods/pull/6966
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Are Modules the Future?
• Tied to headers
• Swift module stability
• Still confusing
• Better than C
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Some Resources
• Clang Docs
https://clang.llvm.org/docs/Modules.html
• Clang Source
https://github.com/llvm-mirror/clang/blob/master/include/clang/
Basic/Module.h
• CocoaPods Source
https://github.com/CocoaPods/CocoaPods/blob/master/lib/
cocoapods/generator/module_map.rb
• Trial & Error
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@segiddins
Mobile Developer Experience @ Square
Exploring Clang Modules
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