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Node.js

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Expressiveness Speed JS

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Underestimated: Ubiquity

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Client Side Server Side JS JS

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Expressiveness Speed JS

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Expressiveness Speed JS V8

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Expressiveness Speed JS V8 ES6+

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Enabling Technologies

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Me, A Systems Programmer?

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Me, A Systems Programmer? That's someone else's job…

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Me, A Systems Programmer?

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Me, A Systems Programmer? "Systems programming" sounds hard… and dangerous

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Me, A Systems Programmer?

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Me, A Systems Programmer? What is "Systems programming" anyway?

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What is Systems Programming? • Programming without a GC • Programming directly against the metal, without abstraction costs • Pay-as-you-go, lightweight runtime, or no runtime • Zero-cost abstractions • When "it doesn't end up mattering" isn't true

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That Doesn't Need to Mean • malloc and free • Assembly Language • Targeting Unix-only or Windows-only • Old-school tools like hand-crafted Makefiles • Fighting with the linker • Writing your entire application in a systems language

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Embedding, Performance, Low Memory

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Fast, Safe, Parallel

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How Does it Work?

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Garbage Collection class  Point
    def  initialize(x,  y)
        @x,  @y  =  x,  y
    end
 end
 
 class  Line
    def  initialize(p1,  p2)
        @p1,  @p2  =  p1,  p2
    end
 
    def  length
        #  compute  length
    end
 end
 def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end Point.new(x1,  y1)

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end Point.new(x1,  y1)

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end Point.new(x1,  y1) Point.new(x2,  y2)

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end Point.new(x1,  y1) Point.new(x2,  y2)

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end Point.new(x1,  y1) Point.new(x2,  y2) Line.new(p1,  p2)

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end Point.new(x1,  y1) Point.new(x2,  y2) Line.new(p1,  p2)

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end Point.new(x1,  y1) Point.new(x2,  y2) Line.new(p1,  p2) later… stop the world…

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Garbage Collection def  length(x1,  y1,  x2,  y2)
    p1  =  Point.new(x1,  y1)
    p2  =  Point.new(x2,  y2)
    line  =  Line.new(p1,  p2)
    line.length
 end

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Ownership

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Ownership is the Right to Destroy

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Right to Destroy pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      println!("Title:  {}",  book.title);   }

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Right to Destroy pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      println!("Title:  {}",  book.title);   }

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Right to Destroy pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      println!("Title:  {}",  book.title);   }

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Right to Destroy pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      println!("Title:  {}",  book.title);   }

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Right to Destroy pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      println!("Title:  {}",  book.title);   }

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Right to Destroy pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      println!("Title:  {}",  book.title);   } note the lack of manual memory management

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Transferring Ownership pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   }

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Transferring Ownership pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  Book)  {      println!("Title:  {}",  book.title);   } error: use of moved value: `book.chapters` note: `book` moved here

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Borrowing v. To receive something with the promise of returning it

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Return this by 5pm on Friday

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Return this by 5pm on Friday

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Return this by 5pm on Friday

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Return this by 5pm on Friday

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Borrowing pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  main()  {      let  book  =  read("book1.txt");      print_book(&book);      println!("Chapters:  {}",  book.chapters.len());   }   fn  print_book(book:  &Book)  {      println!("Title:  {}",  book.title);   }

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Sub-Leasing

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Return this by 5pm on Friday

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Return this by 5pm on Friday

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Return this by 4:30pm on Friday

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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Sub-Leasing fn  main()  {      let  book  =  read_book("book1.txt");      print_book(&book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec
 }   fn  print_book(book:  &Book)  {      print_title(&book);      print_chapters(&book);   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   }

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✏️

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Return this by 5pm on Friday and feel free to change it ✏️

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Return this by 4:30pm on Friday but don't change it ✏️

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✏️

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✏️

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No content

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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fn  main()  {      let  mut  book  =  read_book("book1.txt");      print_book(&mut  book);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec,      bookmark:  u32
 }   fn  print_book(book:  &mut  Book)  {      print_title(&book);      print_chapters(&book);      book.bookmark  =  100;   }   fn  print_title(book:  &Book)  {      println!("Title:  {}",  book.title);   }   fn  print_chapters(book:  &Book)  {      let  len  =  book.chapters.len();      println!("Chapters:  {}",  len);   } Sub-Leasing

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Rules of Borrowing • You can have many outstanding read-only borrows at once • A mutable borrow is unique: no other borrows, mutable
 or read-only, can occur at the same time

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Rules of Borrowing • You can have many outstanding read-only borrows at once • A mutable borrow is unique: no other borrows, mutable
 or read-only, can occur at the same time • These rules are enforced by the compiler, not at runtime

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Read-Only Borrows fn  main()  {      let  book1  =  read_book("book1.txt");      let  book2  =  read_book("book2.txt");      same(&book1,  &book2);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec   }   fn  same(a:  &Book,  b:  &Book)  -­‐>  bool  {      a.title  ==  b.title  &&      a.chapters  ==  b.chapters   }

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Read-Only Borrows fn  main()  {      let  book1  =  read_book("book1.txt");      let  book2  =  read_book("book2.txt");      same(&book1,  &book2);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec   }   fn  same(a:  &Book,  b:  &Book)  -­‐>  bool  {      a.title  ==  b.title  &&      a.chapters  ==  b.chapters   } ✅

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Two Read-Only Borrows fn  main()  {      let  book1  =  read_book("book1.txt");      same(&book1,  &book1);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec   }   fn  same(a:  &Book,  b:  &Book)  -­‐>  bool  {      a.title  ==  b.title  &&      a.chapters  ==  b.chapters   }

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Two Read-Only Borrows fn  main()  {      let  book1  =  read_book("book1.txt");      same(&book1,  &book1);   }   pub  struct  Book  {
    title:  String,      chapters:  Vec   }   fn  same(a:  &Book,  b:  &Book)  -­‐>  bool  {      a.title  ==  b.title  &&      a.chapters  ==  b.chapters   } ✅

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Mutable Borrows Must Be Unique pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book1  =  read_book("book1.txt");      let  mut  book2  =  read_book("book2.txt");      copy(&book1,  &mut  book2);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   }

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Mutable Borrows Must Be Unique pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  book1  =  read_book("book1.txt");      let  mut  book2  =  read_book("book2.txt");      copy(&book1,  &mut  book2);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   } ✅

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pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  mut  book  =  read_book("book1.txt");      copy(&book,  &mut  book);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   } Mutable Borrows Must Be Unique

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pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  mut  book  =  read_book("book1.txt");      copy(&book,  &mut  book);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   } Mutable Borrows Must Be Unique

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pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  mut  book  =  read_book("book1.txt");      copy(&book,  &mut  book);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   } Mutable Borrows Must Be Unique ^~~~ error: cannot borrow `book` as mutable because it is also borrowed as immutable

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Mutable Borrows Must Be Unique pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  mut  book  =  read_book("book1.txt");      copy(&book,  &mut  book);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   }

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Mutable Borrows Must Be Unique pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  mut  book  =  read_book("book1.txt");      copy(&book,  &mut  book);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   } ^~~~ note: previous borrow of `book` occurs here

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Mutable Borrows Must Be Unique pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  mut  book  =  read_book("book1.txt");      copy(&book,  &mut  book);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   }

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Mutable Borrows Must Be Unique pub  struct  Book  {      title:  String,      chapters:  Vec   }   fn  main()  {      let  mut  book  =  read_book("book1.txt");      copy(&book,  &mut  book);   }   fn  copy(a:  &Book,  b:  &mut  Book)  {      b.title  =  a.title;   } ^ note: previous borrow ends here

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Borrowing is the Secret Sauce

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Closures

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Closures fn  main()  {      println!("{:?}",  threes_squared(10));   }   fn  threes_squared(upto:  u32)  -­‐>  Vec  {      (0..upto)          .filter(|i|  i  %  3  ==  0)          .map(|i|  i.pow(2))          .collect()   }

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Closed Over Variables fn  main()  {      println!("{:?}",  threes_squared(10,  "LOG"));   }   fn  threes_squared(upto:  u32,  string:  &str)  -­‐>  Vec  {      (0..upto)          .filter(|i|  i  %  3  ==  0)          .map(|i|  format!("{}:  {}",  string,  i.pow(2)))          .collect()   }

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Equivalent Performance fn  main()  {      println!("{:?}",  threes_squared(10,  "LOG"));   }   fn  threes_squared(upto:  u32,  string:  &str)  -­‐>  Vec  {
    let  v  =  vec![];      loop  {
        if  i  %  3  ==  0  {              v.push(format!("{}:  {}",  string,  i  *  i));          }          if  i  <  upto  {  break;  }
    }      v   }

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Details Abstracted fn  main()  {      println!("{:?}",  threes_squared(10,  "LOG"));   }   fn  threes_squared(upto:  u32,  string:  &str)  -­‐>  Vec  {
    let  v  =  Vec::with_capacity(upto  -­‐  1);      loop  {
        if  i  %  3  ==  0  {              v.push(format!("{}:  {}",  string,  i  *  i));          }          if  i  <  upto  {  break;  }
    }      v   }

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Details Abstracted fn  main()  {      println!("{:?}",  threes_squared(10,  "LOG"));   }   fn  threes_squared(upto:  u32,  string:  &str)  -­‐>  Vec  {
    let  v  =  Vec::with_capacity(upto  -­‐  1);      loop  {
        if  i  %  3  ==  0  {              v.push(format!("{}:  {}",  string,  i  *  i));          }          if  i  <  upto  {  break;  }
    }      v   } Bounds Checks

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Same Ownership Rules

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FnOnce A closure that only runs once and can take ownership from its environment Fn A closure that cannot mutate its environment and can be shared across threads FnMut A closure that can mutate its environment but cannot be shared across threads

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FnOnce fn  main()  {      let  buf  =  String::new();      stdin().read_line(&mut  buf).map(|size|  {
        println!("Read  {}  bytes",  size);          transfer(buf);
    });   }   fn  transfer(string:  String)  {      println!("Got  transferred  {:?}",  string);
 }

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Unified Calling Syntax

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Concurrency

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"Shared Mutable State is the Root of All Evil"

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No content

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Channels Forbid Aliasing

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Channels Forbid Aliasing Functional Forbid Mutation

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Channels Forbid Aliasing Functional Forbid Mutation Rust Forbid Both at the Same Time

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Rules of Borrowing • You can have many outstanding read-only borrows at once • A mutable borrow is unique: no other borrows, mutable
 or read-only, can occur at the same time

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Rules of Borrowing • You can have many outstanding read-only borrows at once • A mutable borrow is unique: no other borrows, mutable
 or read-only, can occur at the same time • You can alias or mutate, but not both at the same time

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Send Safe to transfer across threads (no borrowed values) Sync Safe to share across threads (no racy "interior mutability")

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spawn() fn  main()  {      let  book  =  read_book("book1.txt");      spawn(||  {          println!("{}",  book);      });   }

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spawn() fn  main()  {      let  book  =  read_book("book1.txt");      spawn(||  {          println!("{}",  book);      });   }

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spawn() fn  main()  {      let  book  =  read_book("book1.txt");      spawn(||  {          println!("{}",  book);      });   } ^~~~ error: `book` does not live long enough

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spawn() fn  main()  {      let  book  =  read_book("book1.txt");      spawn(move  ||  {          println!("{}",  book);      });   }

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scoped() fn  main()  {      let  book  =  read_book("book1.txt");      let  guard  =  scoped(||  {          println!("{}",  book);      });
 
    //  do  other  work
 
    let  output  =  guard.join();   }

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scoped() fn  main()  {      let  book  =  read_book("book1.txt");      let  guard  =  scoped(||  {          println!("{}",  book);      });
 
    //  do  other  work
 
    let  output  =  guard.join();  //  default  impl  of  Drop   }

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High Level Productivity

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OO

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OO Syntax struct  Circle  {      x:  f64,      y:  f64,      radius:  f64,   }   impl  Circle  {      fn  area(&self)  -­‐>  f64  {          std::f64::consts::PI  *  (self.radius  *  self.radius)      }   }

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Traits

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Iterators

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Enums with Methods

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Operators

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Thank You!

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Questions? @wycats