Installing swift on CentOS 8

By | March 3, 2021

Previously I worked with swift occasionally and using xCode only. There is my previous post with XML parser written in swift language. Here is my experience in swift installation on Linux platform with initial command line programming example.
The first step – swift installation:
Swift installation
It takes several minutes.

Check swift version:


# swift –version
Swift version 5.3.3 (swift-5.3.3-RELEASE)
Target: x86_64-unknown-linux-gnu

Create simple program:


import Foundation
let date = Date()
print("Now: ", date)
print("Hello, world!")

Execute it in interpreter mode:


# swift helloworld.swift
Now: 2021-03-02 17:38:47 +0000
Hello, world!

Now let us create executable file built from swift sources. Create subdirectory, enter in this directory and generate the package with type executable:


# mkdir helloworld
# cd helloworld/
# swift package init –type executable
Creating executable package: helloworld
Creating Package.swift
Creating README.md
Creating .gitignore
Creating Sources/
Creating Sources/helloworld/main.swift
Creating Tests/
Creating Tests/LinuxMain.swift
Creating Tests/helloworldTests/
Creating Tests/helloworldTests/helloworldTests.swift
Creating Tests/helloworldTests/XCTestManifests.swift

The generated package project file name is Package.swift, also Sources/helloworld/main.swift file was created which is main project source file.
The main.switch file looks like:


print("Hello, world")

Build and run:


# switch run helloworld
-bash: switch: command not found
# swift run helloworld
[2/2] Linking helloworld
Hello, world!

The new executable file located at:


# ls -l ./.build/x86_64-unknown-linux-gnu/debug/helloworld
-rwxr-xr-x. 1 root root 32048 Mar 3 13:22 ./.build/x86_64-unknown-linux-gnu/debug/helloworld

Execute it:


# ./.build/x86_64-unknown-linux-gnu/debug/helloworld
Hello, world!

Now I want to add my helloworld.swift file to the project:


# cp ../helloworld.swift Sources/helloworld/
# ls Sources/helloworld/
helloworld.swift main.swift

Building again. Ops! The compiler gives me errors:


# swift build –target helloworld /Alex/helloworld/Sources/helloworld/helloworld.swift:3:1: error: expressions are not allowed at the top level
print("Now: ", date)
^
/Alex/helloworld/Sources/helloworld/helloworld.swift:4:1: error: expressions are not allowed at the top level
print("Hello, world!")

Changing the source files. For helloworld.swift wrap the code into class definition:


import Foundation
class PrintingMessages
{
   func printing(txt: String="Hello world!")
   {
      let date = Date()
      print("Now: ", date)
      print(txt)
   }
}

In main.cpp we create object of PrintingMessages class and cll printing function:


let printingMessages = PrintingMessages()
printingMessages.printing(txt: "Hello something else!")

Rebuild, link and run:


# swift build –target helloworld
# swift run helloworld
[2/2] Linking helloworld
Now: 2021-03-03 20:49:38 +0000
Hello something else!
# ./.build/x86_64-unknown-linux-gnu/debug/helloworld
Now: 2021-03-03 20:49:52 +0000
Hello something else!

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