Section 1.6. Ruby Jargon and Slang

1.5. Training Your Intuition: Things to Remember

It may truly be said that "everything is intuitive once you understand it." This verity is the heart of this section because Ruby has many features and personality quirks that may be different from what the traditional programmer is used to.

Some readers may feel their time is wasted by a reiteration of some of these points; if that is the case for you, you are free to skip the paragraphs that seem obvious to you. Programmers' backgrounds vary widely; an old-time C hacker and a Smalltalk guru will each approach Ruby from different viewpoints. We hope, however, that a perusal of these following paragraphs will assist many readers in following what some call the Ruby Way.

1.5.1. Syntax Issues

The Ruby parser is complex and relatively forgiving. It tries to make sense out of what it finds instead of forcing the programmer into slavishly following a set of rules. However, this behavior may take some getting used to. Here is a list of things to know about Ruby syntax:

  • Parentheses are usually optional with a method call. These calls are all valid:

    foobar foobar() foobar(a,b,c) foobar a, b, c

  • Given that parentheses are optional, what does x y z mean, if anything? As it turns out, this means, "Invoke method y, passing z as a parameter, and pass the result as a parameter to method x." In short, the statement x(y(z)) means the same thing.

    This behavior will change in the future. Refer to the discussion of poetry mode in section 1.6 "Ruby Jargon and Slang" later in the chapter.

  • Let's try to pass a hash to a method:

    my_method {a=>1, b=>2}

    This results in a syntax error, because the left brace is seen as the start of a block. In this instance, parentheses are necessary:

    my_method({a=>1, b=>2})

  • Now let's suppose that the hash is the only parameter (or the last parameter) to a method. Ruby forgivingly lets us omit the braces:

    my_method(a=>1, b=>2)

    Some people might think that this looks like a method invocation with named parameters. Really it isn't, though it could be used as such.

  • There are other cases in which blank spaces are semi-significant. For example, these four expressions may all seem to mean the same:

    x = y + z x = y+z x = y+ z x = y +z

    And in fact, the first three do mean the same. However, in the fourth case, the parser thinks that y is a method call and +z is a parameter passed to it! It will then give an error message for that line if there is no method named y. The moral is to use blank spaces in a reasonable way.

  • Similarly, x = y*z is a multiplication of y and z, whereas x = y *z is an invocation of method y, passing an expansion of array z as a parameter.

  • In constructing identifiers, the underscore is considered to be lowercase. Thus an identifier may start with an underscore, but it will not be a constant even if the next letter is uppercase.

  • In linear nested-if statements, the keyword elsif is used rather than else if or elif as in some languages.

  • Keywords in Ruby are not really reserved words. When a method is called with a receiver (or in other cases where there is no ambiguity), a keyword may be used as a method name. Do this with caution, remembering that programs should be readable by humans.

  • The keyword then is optional (in if and case statements). Those who want to use it for readability may do so. The same is true for do in while and until loops.

  • The question mark and exclamation point are not really part of the identifier that they modify but should be considered suffixes. Thus we see that although, for example, chop and chop! are considered different identifiers, it is not permissible to use these characters in any other position in the word. Likewise, we use defined? in Ruby, but defined is the keyword.

  • Inside a string, the pound sign (#) is used to signal expressions to be evaluated. That means that in some circumstances, when a pound sign occurs in a string, it has to be escaped with a backslash, but this is only when the next character is a { (left brace), $ (dollar sign), or @ (at sign).

  • Because of the fact that the question mark may be appended to an identifier, care should be taken with spacing around the ternary operator. For example, suppose we have a variable my_flag, which stores either TRue or false. Then the first line of code shown here will be correct, but the second will give a syntax error:

    x = my_flag ? 23 : 45   # OK x = my_flag? 23 : 45    # Syntax error

  • The ending marker =end for embedded documentation should not be considered a token. It marks the entire line and thus any characters on the rest of that line are not considered part of the program text but belong to the embedded document.

  • There are no arbitrary blocks in Ruby; that is, you can't start a block whenever you feel like it as in C. Blocks are allowed only where they are neededfor example, attached to an iterator. The exception is the begin-end block, which can be used basically anywhere.

  • Remember that the keywords BEGIN and END are completely different from the begin and end keywords.

  • When strings bump together (static concatenation), the concatenation is of a lower precedence than a method call. For example:

    str = "First " 'second'.center(20)     # Examples 1 and 2 str = "First " + 'second'.center(20)   # are the same. str = "First second".center(20)        # Examples 3 and 4 str = ("First " + 'second').center(20) # are the same.

  • Ruby has several pseudovariables, which look like local variables but really serve specialized purposes. These are self, nil, true, false, __FILE__, and __LINE__.

1.5.2. Perspectives in Programming

Presumably everyone who knows Ruby (at this point in time) has been a student or user of other languages in the past. This of course makes learning Ruby easy in the sense that numerous features in Ruby are just like the corresponding features in other languages. On the other hand, the programmer may be lulled into a false sense of security by some of the familiar constructs in Ruby and may draw unwarranted conclusions based on past experiencewhich we might term "geek baggage."

Many people are coming to Ruby from Smalltalk, Perl, C/C++, and various other languages. Their presuppositions and expectations may all vary somewhat, but they will always be present. For this reason, we discuss here a few of the things that some programmers may "trip over" in using Ruby:

  • A character in Ruby truly is an integer. It is not a type of its own, as in Pascal, and is not the same as a string of length 1. This is slated to change in the near future so that a character constant will be much the same as a string. As of the time of this writing, this has not happened yet. Consider the following code fragment:

    x = "Hello" y = ?A puts "x[0] = #{x[0]}"   # Prints: x[0] = 72 puts "y = #{y}"         # Prints: y = 65 if y == "A"             # Prints: no   puts "yes" else   puts "no" end

  • There is no Boolean type such as many languages have. TRueClass and FalseClass are distinct classes, and their only instantiations are TRue and false.

  • Many of Ruby's operators are similar or identical to those in C. Two notable exceptions are the increment and decrement operators (++ and --). These are not available in Ruby, neither in "pre" nor "post" forms.

  • The modulus operator is known to work somewhat differently in different languages with respect to negative numbers. The two sides of this argument are beyond the scope of this book; Ruby's behavior is as follows:

    puts (5 % 3)    # Prints 2 puts (-5 % 3)   # Prints 1 puts (5 % -3)   # Prints -1 puts (-5 % -3)  # Prints -2

  • Some may be used to thinking that a false value may be represented as a zero, a null string, a null character, or various other things. But in Ruby, all of these are true; in fact, everything is true except false and nil.

  • In Ruby, variables don't have classes; only values have classes.

  • There are no declarations of variables in Ruby. It is good practice, however, to assign nil to a variable initially. This certainly does not assign a type to the variable and does not truly initialize it, but it does inform the parser that this is a variable name rather than a method name.

  • ARGV[0] is truly the first of the command-line parameters, numbering naturally from zero; it is not the file or script name preceding the parameters, like argv[0] in C.

  • Most of Ruby's operators are really methods; the "punctuation" form of these methods is provided for familiarity and convenience. The first exception is the set of reflexive assignment operators (+=, -=, *=, and so on); the second exception is the following set: = .. ... ! not && and || or != !~.

  • Like most (though not all) modern languages, Boolean operations are always short-circuited; that is, the evaluation of a Boolean expression stops as soon as its truth value is known. In a sequence of or operations, the first true will stop evaluation; in a string of and operations, the first false will stop evaluation.

  • The prefix @@ is used for class variables (which are associated with the class rather than the instance).

  • loop is not a keyword; it is a Kernel method, not a control structure.

  • Some may find the syntax of unless-else to be slightly unintuitive. Because unless is the opposite of if, the else clause will be executed if the condition is true.

  • The simpler Fixnum type is passed as an immediate value and thus may not be changed from within methods. The same is true for true, false, and nil.

  • Do not confuse the && and || operators with the & and | operators. These are used as in C; the former are for Boolean operations, and the latter are for arithmetic or bitwise operations.

  • The and-or operators have lower precedence than the &&-|| operators. See the following code fragment:

    a = true b = false c = true d = true a1 = a && b or c && d   # &&'s are done first a2 = a && (b or c) && d # or is done first puts a1                 # Prints false puts a2                 # Prints true

  • Additionally, be aware that the assignment "operator" has a higher precedence than the and and or operators! (This is also true for the reflexive assignment operators +=, -=, and the others.) For example, in the following code x = y or z looks like a normal assignment statement, but it is really a freestanding expression (equivalent to (x=y) or z, in fact). The third section shows a real assignment statement x = (y or z), which may be what the programmer really intended.

    y = false z = true x = y or z    # = is done BEFORE or! puts x        # Prints false (x = y) or z  # Line 5: Same as previous puts x        # Prints false x = (y or z)  # or is done first puts x        # Prints true

  • Don't confuse object attributes and local variables. If you are accustomed to C++ or Java, you might forget this. The variable @my_var is an instance variable (or attribute) in the context of whatever class you are coding, but my_var, used in the same circumstance, is only a local variable within that context.

  • Many languages have some kind of for loop, as does Ruby. The question sooner or later arises as to whether the index variable can be modified. Some languages do not allow the control variable to be modified at all (printing a warning or error either at compile time or runtime), and some will cheerfully allow the loop behavior to be altered in midstream by such a change. Ruby takes yet a third approach. When a variable is used as a for loop control variable, it is an ordinary variable and can be modified at will; however, such a modification does not affect the loop behavior! The for loop sequentially assigns the values to the variable on each iteration without regard for what may have happened to that variable inside the loop. For example, this loop will execute exactly 10 times and print the values 1 through 10:

    for var in 1..10   puts "var = #{var}"   if var > 5     var = var + 2   end end

  • Variable names and method names are not always distinguishable "by eye" in the immediate context. How does the parser decide whether an identifier is a variable or a method? The rule is that if the parser sees the identifier being assigned a value prior to its being used, it will be considered a variable; otherwise, it is considered to be a method name. (Note also that the assignment does not have to be executed but only seen by the interpreter.)

1.5.3. Ruby's case Statement

Every modern language has some kind of multiway branch, such as the switch statement in C/C++ and Java or the case statement in Pascal. These serve basically the same purpose and function much the same in most languages.

Ruby's case statement is similar to these others, but on closer examination it is so unique that it makes C and Pascal look like close friends. The case statement in Ruby has no precise analogue in any other language that I am familiar with, and this makes it worth additional attention here.

We have already seen the syntax of this statement. We will concentrate here on its actual semantics:

  • To begin with, consider the trivial case statement shown here. The expression shown is compared with the value, not surprisingly, and if they correspond, some_action is performed.

    case expression   when value     some_action end

    Ruby uses the special operator === (called the relationship operator) for this. This operator is also referred to (somewhat inappropriately) as the case equality operator. We say "inappropriately" because it does not always denote equality.

  • Thus the preceding simple statement is equivalent to this statement:

    if value === expression   some_action end

  • However, do not confuse the relationship operator with the equality operator (==). They are utterly different, although their behavior may be the same in many circumstances. The relationship operator is defined differently for different classes and, for a given class, may behave differently for different operand types passed to it.

  • Do not fall into the trap of thinking that the tested expression is the receiver and the value is passed as a parameter to it. The opposite is true (as we saw previously).

  • This points up the fact that x === y is not typically the same as y === x! There will be situations in which this is true, but overall the relationship operator is not commutative. (That is why we do not favor the term case equality operatorbecause equality is always commutative.) In other words, reversing our original example, the following code does not behave the same way:

    case value   when expression     some_action end

  • As an example, consider a string str and a pattern (regular expression) pat, which matches that string. The expression str =~ pat is true, just as in Perl. Because Ruby defines the opposite meaning for =~ in Regexp, you can also say that pat =~ str is true. Following this logic further, we find that (because of how Regexp defines ===) pat === str is also true. However, note that str === pat is not true. This means that this code fragment:

    case "Hello"   when /Hell/     puts "We matched." else   puts "We didn't match." end

    does not do the same thing as this fragment:

    case /Hell/   when "Hello"     puts "We matched." else   puts "We didn't match." end

    If this confuses you, just memorize the behavior. If it does not confuse you, so much the better.

  • Programmers accustomed to C may be puzzled by the absence of break statements in the case statement; such a usage of break in Ruby is unnecessary (and illegal). This is due to the fact that "falling through" is rarely the desired behavior in a multiway branch. There is an implicit jump from each when-clause (or case limb, as it is sometimes called) to the end of the case statement. In this respect, Ruby's case statement resembles the one in Pascal.

  • The values in each case limb are essentially arbitrary. They are not limited to any certain type. They need not be constants but can be variables or complex expressions. Ranges or multiple values can be associated with each case limb.

  • Case limbs may have empty actions (null statements) associated with them. The values in the limbs need not be unique, but may overlap. Look at this example:

    case x   when 0   when 1..5     puts "Second branch"   when 5..10     puts "Third branch" else   puts "Fourth branch" end

    Here a value of 0 for x will do nothing; a value of 5 will print Second branch, even though 5 is also included in the next limb.

  • The fact that case limbs may overlap is a consequence of the fact that they are evaluated in sequence and that short-circuiting is done. In other words, if evaluation of the expressions in one limb results in success, the limbs that follow are never evaluated. Thus it is a bad idea for case limb expressions to have method calls that have side effects. (Of course, such calls are questionable in most circumstances anyhow.) Also, be aware that this behavior may mask runtime errors that would occur if expressions were evaluated. For example:

    case x   when 1..10     puts "First branch"   when foobar()               # Possible side effects?     puts "Second branch"   when 5/0                    # Dividing by zero!     puts "Third branch" else   puts "Fourth branch" end

    As long as x is between 1 and 10, foobar() will not be called, and the expression 5/0 (which would naturally result in a runtime error) will not be evaluated.

1.5.4. Rubyisms and Idioms

Much of this material overlaps conceptually with the preceding pages. Don't worry too much about why we divided it as we did; many of these tidbits were difficult to classify or organize. Our most important motivation was simply to break the information into digestible chunks.

Ruby was designed to be consistent and orthogonal. But it is also complex, and so, like every language, it has its own set of idioms and quirks. We discuss some of these in the following list:

  • alias can be used to give alternate names for global variables and methods.

  • The numbered global variables $1, $2, $3, and so on, cannot be aliased.

  • We do not recommend the use of the "special variables" such as $=, $_, $/, and the rest. Though they can sometimes make code more compact, they rarely make it any clearer; we use them sparingly in this book and recommend the same practice.

  • Do not confuse the .. and ... range operators. The former is inclusive of the upper bound, and the latter is exclusive. For example, 5..10 includes the number 10, but 5...10 does not.

  • There is a small detail relating to ranges that may cause confusion. Given a range m..n, the method end will return the endpoint of the range; its alias last will do the same thing. However, these methods will return the same value n for the range m...n, even though n is not included in the latter range. The method end_excluded? is provided to distinguish between these two situations.

  • Do not confuse ranges with arrays. These two assignments are entirely different:

    x = 1..5 x = [1, 2, 3, 4, 5]

    However, there is a convenient method to_a for converting ranges to arrays. (Many other types also have such a method.)

  • Often we want to assign a variable a value only if it does not already have a value. Because an unassigned variable has the value nil, we can do for example, x = x || 5 shortened to x ||= 5. Beware that the value false will be overwritten just as nil will.

  • In most languages, swapping two variables takes an additional temporary variable. In Ruby, multiple assignment makes this unnecessary: x, y = y, x will interchange the values of x and y.

  • Keep a clear distinction in your mind between class and instance. For example, a class variable such as @@foobar has a classwide scope, but an instance variable such as @foobar has a separate existence in each object of the class.

  • Similarly, a class method is associated with the class in which it is defined; it does not belong to any specific object and cannot be invoked as though it did. A class method is invoked with the name of a class, and an instance method is invoked with the name of an object.

  • In writing about Ruby, the pound notation is sometimes used to indicate an instance methodfor example, we say File.chmod to denote the class method chmod of class File, and File#chmod to denote the instance method that has the same name. This notation is not part of Ruby syntax but only Ruby folklore. We have tried to avoid it in this book.

  • In Ruby, constants are not truly constant. They cannot be changed from within instance methods, but otherwise their values can be changed.

  • In writing about Ruby, the word toplevel is common as both an adjective and a noun. We prefer to use top level as a noun and top-level as an adjective, but our meaning is the same as everyone else's.

  • The keyword yield comes from CLU and may be misleading to some programmers. It is used within an iterator to invoke the block with which the iterator is called. It does not mean "yield" as in producing a result or returning a value but is more like the concept of "yielding a timeslice."

  • The reflexive assignment operators +=, -=, and the rest, are not methods (nor are they really operators); they are only "syntax sugar" or "shorthand" for their longer forms. Thus, to say x += y is really identical to saying x = x + y, and if the + operator is overloaded, the += operator is defined "automagically" as a result of this predefined shorthand.

  • Because of way the reflexive assignment operators are defined, they cannot be used to initialize variables. If the first reference to x is x += 1, an error will result. This will be intuitive to most programmers unless they are accustomed to a language where variables are initialized to some sort of zero or null value.

  • It is actually possible in some sense to get around this behavior. One can define operators for nil such that the initial nil value of the variable produces the result we want. Here is a nil.+ method that will allow += to initialize a String or a Fixnum value, basically just returning other and thus ensuring that nil + other is equal to other:

    def nil.+(other)   other end

    This illustrates the power of Ruby; but whether it is useful or appropriate to code this way is left as an exercise for the reader.

  • It is wise to recall that Class is an object, and Object is a class. We will try to make this clear in a later chapter; for now, simply recite it every day as a mantra.

  • Some operators can't be overloaded because they are built into the language rather than implemented as methods. These are: = .. ... and or not && || ! != !~. Additionally, the reflexive assignment operators (+=, -=, and so on) cannot be overloaded. These are not methods, and it can be argued they are not true operators either.

  • Be aware that although assignment is not overloadable, it is still possible to write an instance method with a name such as foo= (allowing statements such as = 5). Consider the equal sign to be like a suffix.

  • Recall that a "bare" scope operator has an implied Object before it, so that ::Foo means Object::Foo.

  • Recall that fail is an alias for raise.

  • Recall that definitions in Ruby are executed. Because of the dynamic nature of the language, it possible (for example) to define two methods completely differently based on a flag that is tested at runtime.

  • Remember that the for construct (for x in a) is really calling the default iterator each. Any class having this iterator can be walked through with a for loop.

  • Be aware that a method defined at the top level is added to Kernel and is thus a member of Object.

  • A "setter" method (such as foo=) must be called with a receiver; otherwise, it will look like a simple assignment to a local variable of that name.

  • Recall that retry can be used in iterators but not in general loops. In iterators, it causes the reassignment of all the parameters and the restarting of the current iteration.

  • The keyword retry is also used in exception handling. Don't confuse the two usages.

  • An object's initialize method is always private.

  • Where an iterator ends in a left brace (or in end) and results in a value, that value can be used as the receiver for further method calls. For example:

    squares = [1,2,3,4,5].collect do |x| x**2 end.reverse # squares is now [25,16,9,4,1]

  • The idiom if $0 == __FILE__ is sometimes seen near the bottom of a Ruby program. This is a check to see whether the file is being run as a standalone piece of code (TRue) or is being used as some kind of auxiliary piece of code such as a library (false). A common use of this is to put a sort of "main program" (usually with test code in it) at the end of a library.

  • Normal subclassing or inheritance is done with the < symbol:

    class Dog < Animal   # ... end

    But creation of a singleton class (an anonymous class that extends a single instance) is done with the << symbol:

    class << platypus   # ... end

  • When passing a block to an iterator, there is a slight difference between braces ({}) and a do-end pair. This is a precedence issue:

    mymethod param1, foobar do ... end # Here, do-end binds with mymethod mymethod param1, foobar { ... } # Here, {} binds with foobar, assumed to be a method

  • It is somewhat traditional in Ruby to put single-line blocks in braces and multiline blocks in do-end pairs. Examples:

    my_array.each { |x| puts x } my_array.each do |x|   print x   if x % 2 == 0     puts " is even."   else     puts " is odd."   end end

    This habit is not required, and there may be occasions where it is inappropriate to follow this rule.

  • Bear in mind that strings are in a sense two-dimensional; they can be viewed as sequences of characters or sequences of lines. Some may find it surprising that the default iterator each operates on lines (where a "line" is a group of characters terminated by a record separator that defaults to newline); an alias for each is each_line. If you want to iterate by characters, you can use each_byte. The iterator sort also works on a line-by-line basis. There is no iterator each_index for strings because of the ambiguity involved. Do we want to handle the string by character or by line? This all becomes habitual with repeated use.

  • A closure remembers the context in which it was created. One way to create a closure is by using a Proc object. As a crude example, consider the following:

    def power(exponent)   proc {|base| base**exponent} end square = power(2) cube = power(3) a =   # Result is 121 b =    # Result is 25 c =      # Result is 216 d =      # Result is 512

    Observe that the closure "knows" the value of exponent that it was given at the time it was created.

  • However, let's assume that a closure uses a variable defined in an outer scope (which is perfectly legal). This property can be useful, but here we show a misuse of it:

    $exponent = 0 def power   proc {|base| base**$exponent} end $exponent = 2 square = power $exponent = 3 cube = power a =   # Wrong! Result is 1331 b =    # Wrong! Result is 125 # The above two results are wrong because the CURRENT value # of $exponent is being used. This would be true even if it # had been a local variable that had gone out of scope (e.g., # using define_method). c = # Result is 216 d = # Result is 512

  • Finally, consider this somewhat contrived example. Inside the block of the times iterator, a new context is started, so that x is a local variable. The variable closure is already defined at the top level, so it will not be defined as local to the block.

    closure = nil        # Define closure so the name will be known 1.times do           # Start a new context   x = 5              # x is local to this block   closure = { puts "In closure, x = #{x}" } end x = 1 # Define x at top level         # Prints: In closure, x = 5

    Now note that the variable x that is set to 1 is a new variable, defined at the top level. It is not the same as the other variable of the same name. The closure therefore prints 5 because it remembers its creation context with the previous variable x and its previous value.

  • Variables starting with a single @, defined inside a class, are generally instance variables. However, if they are defined outside any method, they are really class instance variables. (This usage is somewhat contrary to most OOP terminology in which a class instance is regarded to be the same as an instance or an object.) Example:

    class Myclass   @x = 1       # A class instance variable   @y = 2       # Another one   def mymethod     @x = 3     # An instance variable     # Note that @y is not accessible here.   end end

    The class instance variable @y in the preceding code example is really an attribute of the class object Myclass, which is an instance of the class Class. (Remember, Class is an object, and Object is a class.) Class instance variables cannot be referenced from within instance methods and, in general, are not very useful.

  • attr, attr_reader, attr_writer, and attr_accessor are shorthand for the actions of defining "setters" and "getters"; they take symbols as arguments (that is, instances of class Symbol).

  • There is never any assignment with the scope operator; for example, the assignment Math::PI = 3.2 is illegal.

1.5.5. Expression Orientation and Other Miscellaneous Issues

In Ruby, expressions are nearly as significant as statements. If you are a C programmer, this will be somewhat familiar to you; if your background is in Pascal, it may seem utterly foreign. But Ruby carries expression orientation even further than C.

In addition, we use this section to remind you of a couple of minor issues regarding regular expressions. Consider them to be a small bonus:

  • In Ruby, any kind of assignment returns the same value that was assigned. Thus we can sometimes take little shortcuts like the ones shown here, but be careful when you are dealing with objects! Remember that these are nearly always references to objects.

    x = y = z = 0      # All are now zero. a = b = c = []     # Danger! a, b, and c now all refer                    # to the SAME empty array. x = 5 y = x += 2         # Now x and y are both 7

    Remember, however, that values such as Fixnums are actually stored as immediate values, not as object references.

  • Many control structures return valuesif, unless, and case. The following code is all valid; it demonstrates that the branches of a decision need not be statements but can simply be expressions:

    a = 5 x = if a < 8 then 6 else 7 end    # x is now 6 y = if a < 8       # y is 6 also; the   6                # if-statement can be else               # on a single line   7                # or on multiple lines. end # unless also works; z will be assigned 4 z = unless x == y then 3 else 4 end t = case a         # t gets assigned   when 0..3        # the value     "low"          # "medium"   when 4..6     "medium" else   "high" end

    Here we indent as though the case started with the assignment. This looks proper to our eyes, but you may disagree.

  • Note by way of contrast that the while and until loops do not return useful values but typically return nil:

    i = 0 x = while (i < 5)   # x is nil   puts i+=1 end

  • The ternary decision operator can be used with statements or expressions. For syntactic reasons (or parser limitations) the parentheses here are necessary:

    x = 6 y = x == 5 ? 0 : 1                 # y is now 1 x == 5 ? puts("Hi") : puts("Bye")  # Prints Bye

  • The return at the end of a method can be omitted. A method always returns the last expression evaluated in its body, regardless of where that happens.

  • When an iterator is called with a block, the last expression evaluated in the block is returned as the value of the block. Thus if the body of an iterator has a statement like x = yield, that value can be captured.

  • Regular expressions: Recall that the multiline modifier /m can be appended to a regex, in which case . (dot) will match a newline character.

  • Regular expressions: Beware of zero-length matches. If all elements of a regex are optional, then "nothingness" will match that pattern, and a match will always be found at the beginning of a string. This is a common error for regex users, particularly novices.

The Ruby Way(c) Solutions and Techniques in Ruby Programming
The Ruby Way, Second Edition: Solutions and Techniques in Ruby Programming (2nd Edition)
ISBN: 0672328844
EAN: 2147483647
Year: 2004
Pages: 269
Authors: Hal Fulton

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