Deep dive into Swift frameworks

Fundamental definitions

To begin with you must have a transparent understanding in regards to the fundamental phrases. For those who already know what’s the distinction between a module, bundle, library or framework you’ll be able to skip this part. Nevertheless in the event you nonetheless have some blended emotions about these items, please learn forward, you received’t remorse it. 😉

Package deal

A bundle consists of Swift supply recordsdata and a manifest file.

A bundle is a set of Swift supply recordsdata. If you’re utilizing Swift Package deal Supervisor you even have to offer a manifest file with a view to make an actual bundle. If you wish to study extra about this instrument, you must test my Swift Package deal Supervisor tutorial.

Instance: that is your bundle:

Sources
    my-source-file.swift
Package deal.swift

It’s also possible to take a look at the open sourced swift-corelibs-foundation bundle by Apple, which is used to construct the Basis framework for Swift.

Library

Library is a packaged assortment of object recordsdata that program can hyperlink towards.

So a library is a bunch of compiled code. You possibly can create two sorts of libraries:

From a extremely easy perspective the one distinction between them is the strategy of “integrating” aka. linking them into your mission. Earlier than I inform you extra about this course of, first we must always discuss object recordsdata.

Mach-O file format

To create packages, builders convert supply code to object recordsdata. The article recordsdata are then packaged into executable code or static libraries.

Whenever you’re compiling the supply recordsdata you’re principally making object recordsdata, utilizing the Mach-O (MachObject) file format. These recordsdata are the core constructing blocks of your purposes, frameworks, and libraries (each dynamic and static).

Linking libraries

Linking refers back to the creation of a single executable file from a number of object recordsdata.

In different phrases:

After the compiler has created all the thing recordsdata, one other program known as to bundle them into an executable program file. That program known as a linker and the method of bundling them into the executable known as linking.

Linking is simply combining all of your object recordsdata into an executable and resolving all of the externals, so the system will be capable of name all of the features contained in the binary.

Static linking

The supply code of the library is actually going to be copied into the applying’s supply. It will lead to a giant executable, it’ll take extra time to load, so the binary may have a slower startup time. Oh, did I point out that in case you are making an attempt to hyperlink the identical library greater than as soon as, the method will fail due to duplicated symbols?

This methodology has benefits as properly, for instance the executable will at all times comprise the proper model of the library, and solely these elements shall be copied into the principle utility which might be actually used, so that you don’t should load the entire stuff, however it looks like dynamic linking goes to be higher in some circumstances.

Dynamic linking

Dynamic libraries are usually not embedded into the supply of the binary, they’re loaded at runtime. Which means apps could be smaller and startup time can considerably be quicker due to the light-weight binary recordsdata. As a free of charge dynamic libraries could be shared with a number of executables to allow them to have decrease reminiscence footprints. That’s why generally they’re being referred as shared libraries.

In fact if the dynamic library is just not out there – or it’s out there however their model is incompatible – your utility received’t run or it’ll crash. However this may be a bonus, as a result of the writer of the dynamic library can ship fixes and your app can profit from these, with out recompilation.

Happily system libraries like UIKit are at all times out there, so that you don’t have to fret an excessive amount of about this problem…

Framework

A framework is a hierarchical listing that encapsulates shared assets, akin to a dynamic shared library, nib recordsdata, picture recordsdata, localized strings, header recordsdata, and reference documentation in a single bundle.

So let’s make this straightforward: frameworks are static or dynamic libraries packed right into a bundle with some further property, meta description for versioning and extra. UIKit is a framework which wants picture property to show a number of the UI components, additionally it has a model description, by the best way the model of UIKit is identical because the model of iOS.

Module

Swift organizes code into modules. Every module specifies a namespace and enforces entry controls on which elements of that code can be utilized outdoors of the module.

With the import key phrase you’re actually importing exterior modules into your sorce. In Swift you’re at all times utilizing frameworks as modules, however let’s return in time for some time to grasp why we would have liked modules in any respect.

import UIKit
import my-awesome-module

Earlier than modules you needed to import framework headers instantly into your code and also you additionally needed to hyperlink manually the framework’s binary inside Xcode. The #import macro actually copy-pasted the entire resolved dependency construction into your code, and the compiler did the work on that massive supply file.

It was a fragile system, issues may go unsuitable with macro definitions, you possibly can simply break different frameworks. That was the explanation for outlining prefixed uppercased very lengthy macro names like: NS_MYSUPERLONGMACRONAME… 😒

There was an different problem: the copy-pasting resulted in non-scalable compile instances. So as to clear up this, precompiled header (PCH) recordsdata had been born, however that was solely a partial resolution, as a result of they polluted the namespace (you recognize in the event you import UIKit in a PCH file it will get out there in in every single place), and no-one actually maintained them.

Modules and module maps

The holy grail was already there, with the assistance of module maps (defining what sort of headers are a part of a module and what’s the binary that has the implementation) we’ve obtained encapsulated modular frameworks. 🎉 They’re individually compiled as soon as, the header recordsdata are defining the interface (API), and the (routinely) linked dylib file accommodates the implementation. Hurray, no have to parse framework headers throughout compilation time (scalability), so native macro definitions received’t break something. Modules can comprise submodules (inheritance), and also you don’t should hyperlink them explicitly inside your (Xcode) mission, as a result of the .modulemap file has all the knowledge that the construct system wants.

Finish of the story, now you recognize what occurs below the hood, once you import Basis or import UIKit.

Now that you recognize the logic behind the entire dynamic modular framework system, we must always begin inspecting the instruments that make this infrastructure attainable.

At all times learn the person pages, aka. RTFM! For those who don’t prefer to learn that a lot, you’ll be able to obtain the instance mission from GitLab and open the makefiles for the essence. There shall be 3 essential classes: C, Swift and Xcode mission examples.

clang

the Clang C, C++, and Goal-C compiler

Clang is a compiler frontend for C languages (C, C++, Goal-C). You probably have ever tried to compiled C code with gcc throughout your college years, you’ll be able to think about that clang is kind of the identical as gcc, however these days it may possibly do much more.

clang -c essential.c -o essential.o #compiles a C supply file

LLVM: compiler backend system, which may compile and optimize the intermediate illustration (IR) code generated by clang or the Swift compiler for instance. It’s language impartial, and it may possibly accomplish that many issues that might match right into a e book, however for now let’s say that LLVM is making the ultimate machine code to your executable.

swiftc

The Swift compiler, there is no such thing as a guide entry for this factor, however don’t fear, simply hearth up swiftc -h and see what can provide to you.

swiftc essential.swift #compiles a Swift supply file

As you’ll be able to see this instrument is what truly can compile the Swift supply recordsdata into Mach-O’s or last executables. There’s a brief instance within the connected repository, you must test on that in the event you’d prefer to study extra in regards to the Swift compiler.

ar

The ar utility creates and maintains teams of recordsdata mixed into an archive. As soon as an archive has been created, new recordsdata could be added and current recordsdata could be extracted, deleted, or changed.

So, in a nutshell you’ll be able to zip Mach-O recordsdata into one file.

ar -rcs myLibrary.a *.o

With the assistance of ar you had been capable of create static library recordsdata, however these days libtool have the identical performance and much more.

ranlib

ranlib generates an index to the contents of an archive and shops it within the archive. The index lists every image outlined by a member of an archive that could be a relocatable object file.

ranlib can create an index file contained in the static lib, so issues are going to be quicker once you’re about to make use of your library.

ranlib myLibrary.a

So ranlib & ar are instruments for sustaining static libraries, often ar takes care of the indexing, and also you don’t should run ranlib anymore. Nevertheless there’s a higher possibility for managing static (and dynamic) libraries that you must study…

libtool

create libraries

With libtool you’ll be able to create dynamically linked libraries, or statically linked (archive) libraries. This instrument with the -static possibility is meant to interchange ar & ranlib.

libtool -static *.o -o myLibrary.a

These days libtool is the principle possibility for increase library recordsdata, you must undoubtedly study this instrument in the event you’re into the subject. You possibly can test the instance mission’s Makefile for more information, or as often you’ll be able to learn the manuals (man libtool). 😉

ld

The ld command combines a number of object recordsdata and libraries, resolves references, and produces an ouput file. ld can produce a last linked picture (executable, dylib, or bundle).

Let’s make it easy: that is the linker instrument.

ld essential.o -lSystem -LmyLibLocation -lmyLibrary -o MyApp

It might probably hyperlink a number of recordsdata right into a single entity, so from the Mach-O’s you’ll be capable of make an executable binary. Linking is important, as a result of the system must resolve the addresses of every methodology from the linked libraries. In different phrases, the executable will be capable of run and your entire features shall be out there for calling. 📱

nm

show identify record (image desk)

With nm you’ll be able to see what symbols are inside a file.

nm myLibrary.a
# 0000000000001000 A __mh_execute_header
#                  U _factorial
# 0000000000001f50 T _main
#                  U _printf
#                  U dyld_stub_binder

As you’ll be able to see from the output, some form of reminiscence addresses are related for a few of symbols. Those who have addresses are literally resolved, all of the others are coming from different libraries (they’re not resolved but). So because of this they’ll be resolved at runtime. The opposite possibility is that you need to hyperlink them. 😅

otool

object file displaying instrument

With otool you’ll be able to look at the contents of Mach-O recordsdata or libraries.

otool -L myLibrary.a
otool -tV myLibrary.a

For instance you’ll be able to record the linked libraries, or see the disassembled textual content contents of the file. It’s a extremely useful instrument in the event you’re acquainted with the Mach-O file format, additionally good one to make use of for reverse-engineer an current utility.

lipo

create or function on common recordsdata

With the assistance of the lipo instrument you’ll be able to create common (multi-architecture) recordsdata. Often this instrument is used for creating common frameworks.

lipo -create -output myFramework.framework gadgets.framework simulator.framework

Think about the next situation: you construct your sources each for arm7 and i386. On an actual machine you’d have to ship the arm7 model, however for the iOS simulator you’ll want the i386 one. With the assistance of lipo you’ll be able to mix these architectures into one, and ship that framework, so the top consumer don’t have to fret about this problem anymore.

Learn on the article to see the way it’s performed. 👇

These instruments could be invoked from the command line as properly, however they’re far more associated to Xcode than those earlier than. Let’s have a fast walk-through.

xcode-select

Manages the energetic developer listing for Xcode and BSD instruments. You probably have a number of variations of Xcode in your machine this instrument can simply swap between the developer instruments offered by the induvidual variations.

xcode-select --switch path/to/Xcode.app

xcrun

Run or find improvement instruments and properties. With xcrun you’ll be able to principally run something that you would be able to handle from Xcode.

xcrun simctl record #record of simulators

codesign

Create and manipulate code signatures

It might probably signal your utility with the correct signature. Often this factor failed once you had been making an attempt to signal your app earlier than automated signing was launched.

codesign -s "Your Firm, Inc." /path/to/MyApp.app
codesign -v /path/to/MyApp.app

xcodebuild

construct Xcode initiatives and workspaces

That’s it. It’ll parse the Xcode mission or workspace file and executes the suitable buid instructions primarily based on it.

xcodebuild -project Instance.xcodeproj -target Instance
xcodebuild -list
xcodebuild -showsdks

FAT frameworks

Find out how to make a closed supply common FATtened (multi-architecture) Swift framework for iOS?

So we’re right here, the entire article was made for studying the logic behind this tutorial.

To begin with, I don’t wish to reinvent the wheel, as a result of there’s a superbly written article that you must learn. Nevertheless, I’d like to offer you some extra detailed rationalization and just a little modification for the scripts.

Skinny vs. FAT frameworks

Skinny frameworks accommodates compiled code for just one structure. FAT frameworks then again are containing “slices” for a number of architectures. Architectures are principally referred as slices, so for instance the i386 or arm7 slice.

This implies, in the event you compile a framework just for i386 and x86_64 architectures, it should work solely on the simulator and horribly fail on actual gadgets. So if you wish to construct a really common framework, you need to compile for ALL the prevailing architectures.

Constructing a FAT framework

I’ve a excellent news for you. You simply want one little construct part script and an combination goal with a view to construct a multi-architecture framework. Right here it’s, shamelessly ripped off from the supply article, with some further modifications… 😁

set -e
BUILD_PATH="${SRCROOT}/construct"
DEPLOYMENT_PATH="${SRCROOT}"
TARGET_NAME="Console-iOS"
FRAMEWORK_NAME="Console"
FRAMEWORK="${FRAMEWORK_NAME}.framework"
FRAMEWORK_PATH="${DEPLOYMENT_PATH}/${FRAMEWORK}"

# clear the construct folder
if [ -d "${BUILD_PATH}" ]; then
    rm -rf "${BUILD_PATH}"
fi

# construct the framework for each structure utilizing xcodebuild
xcodebuild -target "${TARGET_NAME}" -configuration Launch 
    -arch arm64 -arch armv7 -arch armv7s 
    only_active_arch=no defines_module=sure -sdk "iphoneos"

xcodebuild -target "${TARGET_NAME}" -configuration Launch 
    -arch x86_64 -arch i386 
    only_active_arch=no defines_module=sure -sdk "iphonesimulator"

# take away earlier model from the deployment path
if [ -d "${FRAMEWORK_PATH}" ]; then
    rm -rf "${FRAMEWORK_PATH}"
fi

# copy freshly constructed model to the deployment path
cp -r "${BUILD_PATH}/Launch-iphoneos/${FRAMEWORK}" "${FRAMEWORK_PATH}"

# merge all of the slices and create the fats framework
lipo -create -output "${FRAMEWORK_PATH}/${FRAMEWORK_NAME}" 
    "${BUILD_PATH}/Launch-iphoneos/${FRAMEWORK}/${FRAMEWORK_NAME}" 
    "${BUILD_PATH}/Launch-iphonesimulator/${FRAMEWORK}/${FRAMEWORK_NAME}"

# copy Swift module mappings for the simulator
cp -r "${BUILD_PATH}/Launch-iphonesimulator/${FRAMEWORK}/Modules/${FRAMEWORK_NAME}.swiftmodule/" 
    "${FRAMEWORK_PATH}/Modules/${FRAMEWORK_NAME}.swiftmodule"

# clear up the construct folder once more
if [ -d "${BUILD_PATH}" ]; then
    rm -rf "${BUILD_PATH}"
fi

You possibly can at all times look at the created framework with the lipo instrument.

lipo -info Console.framework/Console
#Architectures within the fats file: Console.framework/Console are: x86_64 i386 armv7 armv7s arm64

Utilization

You simply should embed your model new framework into the mission that you just’d like to make use of and set some paths. That’s it. Nearly…

Delivery to the App Retailer

There is just one problem with fats architectures. They comprise slices for the simulator as properly. If you wish to submit your app to the app retailer, you need to minimize off the simulator associated codebase from the framework. The rationale behind that is that no precise actual machine requires this chunk of code, so why submit it, proper?

APP_PATH="${TARGET_BUILD_DIR}/${WRAPPER_NAME}"

# take away unused architectures from embedded frameworks
discover "$APP_PATH" -name '*.framework' -type d | whereas learn -r FRAMEWORK
do
    FRAMEWORK_EXECUTABLE_NAME=$(defaults learn "$FRAMEWORK/Information.plist" CFBundleExecutable)
    FRAMEWORK_EXECUTABLE_PATH="$FRAMEWORK/$FRAMEWORK_EXECUTABLE_NAME"
    echo "Executable is $FRAMEWORK_EXECUTABLE_PATH"

    EXTRACTED_ARCHS=()

    for ARCH in $ARCHS
    do
        echo "Extracting $ARCH from $FRAMEWORK_EXECUTABLE_NAME"
        lipo -extract "$ARCH" "$FRAMEWORK_EXECUTABLE_PATH" -o "$FRAMEWORK_EXECUTABLE_PATH-$ARCH"
        EXTRACTED_ARCHS+=("$FRAMEWORK_EXECUTABLE_PATH-$ARCH")
    performed

    echo "Merging extracted architectures: ${ARCHS}"
    lipo -o "$FRAMEWORK_EXECUTABLE_PATH-merged" -create "${EXTRACTED_ARCHS[@]}"
    rm "${EXTRACTED_ARCHS[@]}"

    echo "Changing authentic executable with thinned model"
    rm "$FRAMEWORK_EXECUTABLE_PATH"
    mv "$FRAMEWORK_EXECUTABLE_PATH-merged" "$FRAMEWORK_EXECUTABLE_PATH"

performed

This little script will take away all of the pointless slices from the framework, so that you’ll be capable of submit your app by way of iTunesConnect, with none points. (ha-ha-ha. 😅)

NOTE: You need to add this final script to your utility’s construct phases.

If you wish to get acquainted with the instruments behind the scenes, this text will make it easier to with the fundamentals. I couldn’t discover one thing like this however I wished to dig deeper into the subject, so I made one. I hope you loved the article. 😉