Ruby

1. Ruby and other languages…

2. Valuable Reference The Ruby Programming Language, Flanagan & Matsumoto (creator of Ruby)

3. What do you need to know about a new language? • How to execute • Program structure • Variables • name, keywords, binding, scope, lifetime • Data types • type system • primitives, strings, arrays, hashes • pointers/references • type conversions and equality • Expressions • Operators, overloading, booleans, short-circuiting, conditional expression • Referential transparency • Statements vs Expressions • Control flow • conditionals • loops • Functions • Classes • Exception handling • Other features • Threads • Reflection • Libraries • Functional Language – other aspects, covered later • QUICK EX: With a partner • how do you learn a new programming language? • What types of programs do you write?

4. Think like a compiler • Tokens: • int • count • = • 20 • ; • Grammar: • Based on BNF • Scanner (lexical analyzer): identifies the tokens of a program statement • Parser (syntax analyzer): determines whether the statement is valid, based on the language definition/grammar • int count = 20;

5. Ruby Program Structure Expression vs statement? Basic unit is expression Primary expressions: true, false, nil, self, number and string literals, variable references (all represent values) Expressions: arithmetic, boolean Methods Classes Modules

6. Get started - interactive • open IRB • puts “say Hi” say Hi • nil • nil is return… ruby has expressions, not statements

7. Ruby Statement Structure Compare to Java/C++/Python * think: how does interpreter recognize tokens/statement? • Whitespace: mostly ignored • Statement separators: newline • use caution if statement doesn’t fit on one line • insert newline after operator, period or comma • OR escape the newline *

8. Ruby Comments # This is a comment OR =begin This is a longer comment. =begin/=end must be at the start of a line =end

9. Ruby Methods Compare to Java/C++/Python • No ( ) needed for function invocation • if use (), don’t put space after fn name! • f(3+2)+1 != f (3+2)+1 • Try it: “hello”.center 20 “hello”.delete “lo” • What’s good practice? Here are some thoughts: • http://stackoverflow.com/questions/340624/do-you-leave-parentheses-in-or-out-in-ruby

10. Block Structure block surrounded by { } often call this the “body” never delimit with { } block delimited by “end” Compare to Java/C++ 10.times { puts “hello” } x = 5 unless x == 10 print x end • Blocks can be nested. Indent for clarity.

11. Variables Compare to Java/C++/Fortran • length: no limit (afaik) • valid characters: • letters, numbers, _ • can’t start with number • $ used as first character of global var • @/@@ used to identify instance and class variables • ? (convention) end method name with ? if returns boolean • ! (convention) end method name with ! if dangerous • = used to make assignments (covered with classes) • no other punctuation • support for Unicode • first letter (enforced by ruby): • Constants, classes and modules begin with A-Z • case sensitive

12. Keywords vs Reserved Words Compare to Java/C++ many words have special meaning (e.g. if, true, def, etc.) Keyword: has special meaning, but can be used as variable name Reserved: can’t be used as variable Ruby: keyword… can prefix with @, @@ or $ and use as variable name

13. The Concept of Binding • A binding is an association, such as: • bind type of variable • bind operation to symbol (e.g., meaning of *) • bind function to its definition • Binding timeis the time at which a binding takes place. • Type binding • may be static or dynamic • explicit or implicit

14. Possible Binding Times Language design time -- bind operator symbols to operations : sum = sum + count Language implementation time-- bind type to a representation : int => number of bits, etc. Compile time -- bind a variable to a type: int count; Link time – bind library subprogram to code: cout << x; Load time -- bind a FORTRAN 77 variable to a memory cell (or a C static variable) Runtime-- bind a nonstatic local variable to a memory cell

15. Static vs. Dynamic Binding A binding is static if it first occurs before run time and remains unchanged throughout program execution. A binding is dynamic if it first occurs during execution or can change during execution of the program NOTE: doesn't consider paging etc. which is at the hardware level

16. Dynamic Type Binding How are generic program units done in C++? Java? • Type not specified by declaration, not determined by name (JavaScript, PHP, Ruby) • Specified through an assignment statement list = [2, 4.33, 6, 8]; list = 17.3; • Advantage: flexibility (generic program units) • Disadvantages: • High cost (dynamic type checking requires run-time descriptors, normally interpreted) • Type error detection by the compiler is difficult

17. Quick Exercise How would dynamic types be implemented? What data structure(s) would you use? How does this impact your code – consider efficiency, reliability. Specifically, think about implementing +, where 3 + 5 is 8 and “hello” + “ world” is “hello world” Turn in for class participation (no specific format, just show some thought)

18. Dynamic Type Issue i = x; // desired, x is scalar i = y; // typed accidentally, y is array

19. Explicit/Implicit Declaration • An explicit declarationis a program statement used for declaring the types of variables: int count; • An implicit declarationis a default mechanism for specifying types of variables (the first appearance of the variable in the program) • Both create static bindings to types (i.e., type doesn’t change during execution of program) • FORTRAN, PL/I, BASIC, and Perl provide implicit declarations • Advantage: writability • Disadvantage: reliability • Perl: @ is array, % is hash, $ is scalar • Fortran: I-N integer, others single precision, can override

20. Ruby Data Types: numbers C++ has unsigned ints, Java does not… concept doesn’t apply to Ruby – why? COBOL was for business… inherent big decimal. Java/C# provide. C++ does not. Adv: accuracy. Disadv: waste space • Numeric • Integer – allows base 8, 16, 2 (binary) • Fixnum: fit in 31 bits • Bignum: arbitrary size • Float – includes scientific notation • Complex • BigDecimal: use decimal rather than binary rep • Rational

21. A few details -7/3 = -3 in Ruby, -2 in Java/C++ div = integer division, e.g., 7.div 3 fdiv = floating point division, e.g., 7.fdiv 3 quo = rational division Float::MAX Infinity Numbers are immutable (as you’d expect)

22. Ruby Data Types: strings Other languages with interpolation? • String literals – single quote • ‘A ruby string’ • ‘Didn\’t you have fun?’ • Only escape \’ or \\ • newlines are embedded if multi-line • String literals – double quote • normal escape sequences (\t, \n etc) • string interpolation w=5 h=4 puts "The area is #{w*h}"

23. More strings Java converts right-hand to string, Ruby doesn’t • Strings are mutable in Ruby • + is concatenation (often prefer interpolation) age = 32 puts "I am " + age.to_s • << is append s = "Hello" s << " World" puts s • Extract characters puts s[0, 5] • * repeats text puts "hey " * 5

24. Characters Python also has strings of length 1, not primitive chars Does Java support unicode? Does C++? • Changed from Ruby 1.8 to Ruby 1.9 • Characters are now strings of length 1 • Not covered • multi-byte characters (need for unicode… 16-bit encoding, first 128 the same as ASCII) • specify encodings (e.g., ASCII-8BIT, BINARY, US-ASCII, ASCII, ISO-8859-15, UTF-8) • many other String methods, such as downcase, upcase, chop, delete, tr, etc.

25. Program Execution • Ruby is a scripting language • No special main method • In general, script starts executing with line 1, continues until all lines executed • Methods/classes come into existence when they are read in the file • May use BEGIN/END (not common to do) • BEGIN { # global init code ] • END { #global shutdown code] • if multiple BEGINS, interpreter executes in order read

26. Getting started – command line Open text editor puts “say Hi” save file as demo1.rb at command line: ruby demo1.rb

27. String Access: Quick Exercise Compare to C/C++ • Can use [] with: • [ix] • [ix,len] • [ix..ix] • [-ix] • stringname.length, etc. • if index too large, just returns nil • Try: • s = "Sunday, Monday, Tuesday, Wednesday, Thursday, Friday" • Find different ways to extract Sunday, Monday and Friday using the index options shown above • Use different ways to modify the string (e.g., convert the string to: Monday, day, Tuesday, Wednesday, Thursday, Saturday) • Nothing to submit; no right answers – just play!

28. Get started Do Ruby Intro homework

29. Topic Summary • Language concepts • Effect of syntax on compilation • Binding • overview • static vs dynamic • explicit vs implicit types • Scripting language • Keywords vsReserved words • Ruby Basics • program structure • program execution • block structure • methods • comments • variables • strings • interpolation • numbers