I’m learning about Swift on Linux and using modules to wrap C libraries. One of the things I wanted to do was use libdispatch with blocks from Swift. I thought it would be easy to use a module to wrap <dispatch/dispatch.h>.
I made a module called “CDispatch” with a module.modulemap like this ======= module CDispatch [system] { header "/usr/include/dispatch/dispatch.h" export * link "dispatch" } ======== Then I created a little demo project called gcd4 whose Source/main.swift prints some things and then uses a dispatch queue and a block to print a message after 2 seconds delay. ========= CDispatch.dispatch_after(time, queue, { print("Delayed!") }) ======== The entire project is checked in at https://github.com/sheffler/gcd4 <https://github.com/sheffler/gcd4> and the CDispatch module is checked in at https://github.com/sheffler/CDispatch <https://github.com/sheffler/CDispatch> If I try to “swift build” the project, it almost works but reports that dispatch_after is not found. It seems that this function is not defined if the “blocks" feature is not provided at compilation time. ======== Compiling Swift Module 'gcd4' (1 sources) /home/sheffler/swift/gcd4/Sources/main.swift:42:1: error: module 'CDispatch' has no member named 'dispatch_after' CDispatch.dispatch_after(time, queue, { ^~~~~~~~~ ~~~~~~~~~~~~~~ <unknown>:0: error: build had 1 command failures swift-build: exit(1): ["/home/sheffler/src/swift-2.2-SNAPSHOT-2015-12-01-b-ubuntu14.04/usr/bin/swift-build-tool", "-f", "/home/sheffler/swift/gcd4/.build/debug/gcd4.o/llbuild.yaml”] ======== I got the demo program to work by first using “swift build” to retrieve the CDispatch module, and then manually running the compiler like this (and including the “-Xcc -fblocks” arguments) swiftc -v -o gcd4 Sources/main.swift -I .build/debug -j8 -Onone -g -Xcc -fblocks -Xcc -F-module-map=Packages/CDispatch-1.0.0/module.modulemap -I Packages/CDispatch-1.0.0 -I /usr/local/include This is all pretty neat! I’ve got blocks, dispatch queues and ARC on Ubuntu. I have one question and one remark. - Am i missing something about how to create the CDispatch module? Why can’t “swift build” build this? - Creating Git repositories for simple modules that wrap a single library and include a header file or two seems like too much. I would love to have been able to create a sub-directory in my project with a modulemap that includes <dispatch/dispatch.h> and links libdispatch.so Thanks Tom P.S. - I tried to make this easy to check out and compile
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