Go Beyond Paradigms - Speaker Deck

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T h e o r y i n P r a c t i c e GO BEYOND PARADIGMS Is Go object-oriented? Is that a good question? Understand language features, use the right patterns. Luciano Ramalho @ramalhoorg

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2 Sometimes you need a blank template.

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FLUENT PYTHON 3 5 stars at amazon.de Published in 9 languages: •Chinese (simpliﬁed) •Chinese (traditional) •English •French •Japanese •Korean •Polish •Brazilian Portuguese •Russian 2nd edition: late 2020

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TECH REVIEWER OF THE BRAZILIAN EDITION OF GOPL GOPL:  The Go Programming Language Donovan & Kernighan 4

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WORKSHOP: INTRODUCING GO WITH TDD 5 https://tgo.li/wtm-tdd-go

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EMPORIO CELESTIAL By Jorge Luis Borges 6

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PARADIGMS Programming language categories 10

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A GOOD SURVEY-STYLE TEXTBOOK Programming Language Pragmatics,  4th edition (2015) Michael L. Scott 11

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GCD ASM X86 Máximo divisor comum em assembly x86 (Scott, 2015) 12

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GCD IN C, OCAML, PROLOG 13

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GCD IN GO Imperative style Functional style 14

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GCD IN GO Imperative style Functional style 15 Bad ﬁt for Go:  no tail-call optimisation

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SCOTT’S CLASSIFICATION 16 Programming Language Pragmatics,  4th edition (2015) Michael L. Scott

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SCOTT’S CLASSIFICATION (ZOOM) 17

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SCOTT’S CLASSIFICATION (ZOOM) 18 ???

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ANOTHER BOOK Princípios de Linguagens de Programação  (2003) Ana Cristina Vieira de Melo Flávio Soares Corrêa da Silva 19

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21 Lógicas

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THE GO FAMILY TREE 22 source:  The Go Programming Language  Donovan & Kernighan

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CATEGORIES? Ontologies are so 1900’s 23

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A CLASSIFICATION BASED ON HARD FACTS 24

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A CLASSIFICATION BASED ON HARD FACTS 25 “Noble” gases!?

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“Ontology is overrated.” Clay Shirky 26 https://tgo.li/onto-over

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A BETTER APPROACH Fundamental Features of Programming Languages 27

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HANDS-ON PROGRAMMING LANGUAGE THEORY 28

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A PAPER PRESENTING THE APPROACH 29

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A PAPER PRESENTING THE APPROACH 30

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A PAPER PRESENTING THE APPROACH 31

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A PAPER PRESENTING THE APPROACH 32

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HANDS-ON WITH RACKET (A MODERN SCHEME DIALECT) 33

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FEATURES Understand core features, not just syntax and libraries 34

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SAMPLE FEATURES ✖ LANGUAGES 35 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 36 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural Functions as objects Classes as objects

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SAMPLE FEATURES ✖ LANGUAGES 37 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 38 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 39 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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SAMPLE FEATURES ✖ LANGUAGES 40 Common Lisp C Java Python Go First-class functions ✔ ∗ ✔ ✔ ✔ First-class types ✔ ✔ Iterators ∗ ✔ ✔ ∗ Variable model reference value* value and reference reference value* and reference* Type checking dynamic static static dynamic static Type expression structural nominal nominal structural structural

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DESIGN PATTERNS When languages fall short 41

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GOF: CLASSIC BOOK BY THE “GANG OF FOUR” Design Patterns: Elements of Reusable Object-Oriented Software (1995) Erich Gamma  Richard Helm  Ralph Johnson  John Vlissides 42

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NOT EVERY PATTERN IS UNIVERSAL Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley, 1995), p. 4. 43

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NOT EVERY PATTERN IS UNIVERSAL Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley, 1995), p. 4. 44

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NOT EVERY PATTERN IS UNIVERSAL Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley, 1995), p. 4. 45

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ITERABLES & ITERATORS An excellent abstraction 49

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ITERATION IN C 50 #include int main(int argc, char *argv[]) { for(int i = 0; i < argc; i++) printf("%s\n", argv[i]); return 0; }

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ITERATION IN GO 51

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ITERATION IN C AND GO 52 #include int main(int argc, char *argv[]) { for(int i = 0; i < argc; i++) printf("%s\n", argv[i]); return 0; }

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FOREACH IN BARBARA LISKOV'S CLU 53 CLU Reference Manual — B. Liskov et. al. — © 1981 Springer-Verlag — also available online from MIT: http://publications.csail.mit.edu/lcs/pubs/pdf/MIT-LCS-TR-225.pdf © 2010 Kenneth C. Zirkel — CC-BY-SA

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ITERABLE OBJECTS: THE KEY TO FOREACH • Python, Java, CLU etc. let programmers deﬁne iterable objects              • In Go, only array, slice, string, map, channel are supported by for/range 55 for item in an_iterable: process(item) for item in an_iterable: process(item)

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ITERATOR PATTERN The classic recipe 56

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58 Head First Design Patterns Poster  O'Reilly  ISBN 0-596-10214-3

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CLASSIC  ITERATOR IN GO The classic recipe in Go 59

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USING A CLASSIC ITERATOR IN GO for/range not supported 60

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IMPLEMENTING A CLASSIC ITERATOR IN GO Not too bad  (if you like Java) 61

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CHANNEL-BASED ITERATOR Leveraging Go features 62

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for/range supported! USING A CHANNEL-BASED ITERATOR 63

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USAGE COMPARISON 64

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IMPLEMENTING A CHANNEL-BASED ITERATOR 65

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IMPLEMENTATION COMPARISON 66

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CONSIDERING THE OPTIONS A classic two-method iterator is more cumbersome to use and to implement. It is used in the standard library. Ex: buﬃo.Scanner (with methods called Scan and Text). Clients can quit at any time; iterator will be garbage-collected. A channel-based iterator is simpler to use and to implement. However, there is a context switch cost to run a coroutine, and the coroutine may leak if it does not run to completion. Allowing clients to cancel the iterator requires an additional channel for signaling. 67

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STRATEGY IN GO Leveraging core features of Go 68

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CHOOSE AN ALGORITHM AT RUN TIME 69

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70 Context Strategy Concrete strategies CHOOSE AN ALGORITHM AT RUN TIME

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STRATEGY IN GO “Classic” implementation with an interface Implementation with ﬁrst-class functions 71

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TESTS 72 interface/strategy_test.go https://tgo.li/gobeyond2019

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TESTS (CONT.) 73 interface/strategy_test.go https://tgo.li/gobeyond2019

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CUSTOMER AND LINE ITEM 74 interface/store.go https://tgo.li/gobeyond2019

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CONTEXT AND STRATEGY 75 interface/strategy.go https://tgo.li/gobeyond2019 Context Strategy

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CONCRETE STRATEGY 76 interface/store.go https://tgo.li/gobeyond2019

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MORE CONCRETE STRATEGIES 77 interface/store.go https://tgo.li/gobeyond2019

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STRATEGY WITH FIRST CLASS FUNCTIONS 78

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TESTS WITH FUNCTIONS 79

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CONCRETE STRATEGIES AS FUNCTIONS 80

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WHICH IS MORE IDIOMATIC GO? Interfaces v. Functions 81

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WHICH IS MORE GOISH? Interfaces v. Functions 82

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INTERFACES V. FIRST CLASS FUNCTIONS In the standard library, one-method interfaces are common. 83

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INTERFACES V. FIRST CLASS FUNCTIONS But the http package supports both ways*: 84 *Kumar Iyer (ThoughtWorks): Higher-order functions vs interfaces in golang http://bit.ly/2j39uKh

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WRAPPING UP Why learn the fundamentals 85

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INSTEAD OF PARADIGMS… 86 A B C D E F G

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FOCUS ON FUNDAMENTAL FEATURES 87 A B C D E F G

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…to decide whether a particular pattern or implementation makes sense. FEATURES ARE THE BEST GUIDE… A B C D E F G + ✔ ✔ ✔ ✔ + ✔ ✔ ✔ ✔ + ✔ ✔ ✔ ✔ ✔

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WHY LEARN THE FUNDAMENTALS* • Learn new languages more easily • Make the most of language features • Know how to choose alternative ways of implementation • Make good use of design patterns • Debug complicated bugs • Mimic useful features in languages where they are missing 89 Inspired by Programming Language Pragmatics Michael L. Scott *

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Luciano Ramalho luciano.ramalho@thoughtworks.com  Twitter: @ramalhoorg Github: https://github.com/standupdev Slides: speakerdeck.com/ramalho VIELEN DANK !