Returns an indication of the number of arguments accepted by a method. Returns a nonnegative integer for methods that take a fixed number of arguments. For Ruby methods that take a variable number of arguments, returns -n-1, where n is the number of required arguments. Keyword arguments will be considered as a single additional argument, that argument being mandatory if any keyword argument is mandatory. For methods written in C, returns -1 if the call takes a variable number of arguments.
class C def one; end def two(a); end def three(*a); end def four(a, b); end def five(a, b, *c); end def six(a, b, *c, &d); end def seven(a, b, x:0); end def eight(x:, y:); end def nine(x:, y:, **z); end def ten(*a, x:, y:); end end c = C.new c.method(:one).arity #=> 0 c.method(:two).arity #=> 1 c.method(:three).arity #=> -1 c.method(:four).arity #=> 2 c.method(:five).arity #=> -3 c.method(:six).arity #=> -3 c.method(:seven).arity #=> -3 c.method(:eight).arity #=> 1 c.method(:nine).arity #=> 1 c.method(:ten).arity #=> -2 "cat".method(:size).arity #=> 0 "cat".method(:replace).arity #=> 1 "cat".method(:squeeze).arity #=> -1 "cat".method(:count).arity #=> -1
Returns the class or module on which this method is defined. In other words,
meth.owner.instance_methods(false).include?(meth.name) # => true
holds as long as the method is not removed/undefined/replaced, (with private_instance_methods instead of instance_methods if the method is private).
See also Method#receiver.
(1..3).method(:map).owner #=> Enumerable
Checks if the object is shareable by ractors.
Ractor.shareable?(1) #=> true -- numbers and other immutable basic values are frozen Ractor.shareable?('foo') #=> false, unless the string is frozen due to # freeze_string_literals: true Ractor.shareable?('foo'.freeze) #=> true
See also the “Shareable and unshareable objects” section in the Ractor class docs.
When max is an Integer, rand returns a random integer greater than or equal to zero and less than max. Unlike Kernel.rand, when max is a negative integer or zero, rand raises an ArgumentError.
prng = Random.new prng.rand(100) # => 42
When max is a Float, rand returns a random floating point number between 0.0 and max, including 0.0 and excluding max.
prng.rand(1.5) # => 1.4600282860034115
When range is a Range, rand returns a random number where range.member?(number) == true.
prng.rand(5..9) # => one of [5, 6, 7, 8, 9] prng.rand(5...9) # => one of [5, 6, 7, 8] prng.rand(5.0..9.0) # => between 5.0 and 9.0, including 9.0 prng.rand(5.0...9.0) # => between 5.0 and 9.0, excluding 9.0
Both the beginning and ending values of the range must respond to subtract (-) and add (+)methods, or rand will raise an ArgumentError.
Seeds the system pseudo-random number generator, with number. The previous seed value is returned.
If number is omitted, seeds the generator using a source of entropy provided by the operating system, if available (/dev/urandom on Unix systems or the RSA cryptographic provider on Windows), which is then combined with the time, the process id, and a sequence number.
srand may be used to ensure repeatable sequences of pseudo-random numbers between different runs of the program. By setting the seed to a known value, programs can be made deterministic during testing.
srand 1234 # => 268519324636777531569100071560086917274 [ rand, rand ] # => [0.1915194503788923, 0.6221087710398319] [ rand(10), rand(1000) ] # => [4, 664] srand 1234 # => 1234 [ rand, rand ] # => [0.1915194503788923, 0.6221087710398319]
Returns a string, using platform providing features. Returned value is expected to be a cryptographically secure pseudo-random number in binary form. This method raises a RuntimeError if the feature provided by platform failed to prepare the result.
In 2017, Linux manpage random(7) writes that “no cryptographic primitive available today can hope to promise more than 256 bits of security”. So it might be questionable to pass size > 32 to this method.
Random.urandom(8) #=> "\x78\x41\xBA\xAF\x7D\xEA\xD8\xEA"
Basically the same as ::new. However, if class Thread is subclassed, then calling start in that subclass will not invoke the subclass’s initialize method.
Raises an exception from the given thread. The caller does not have to be thr. See Kernel#raise for more information.
Thread.abort_on_exception = true a = Thread.new { sleep(200) } a.raise("Gotcha")
This will produce:
prog.rb:3: Gotcha (RuntimeError) from prog.rb:2:in `initialize' from prog.rb:2:in `new' from prog.rb:2
Returns the current backtrace of the target thread.
A convenience method for TracePoint.new, that activates the trace automatically.
trace = TracePoint.trace(:call) { |tp| [tp.lineno, tp.event] } #=> #<TracePoint:enabled> trace.enabled? #=> true
Line number of the event
With no arguments, raises the exception in $! or raises a RuntimeError if $! is nil. With a single String argument, raises a RuntimeError with the string as a message. Otherwise, the first parameter should be an Exception class (or another object that returns an Exception object when sent an exception message). The optional second parameter sets the message associated with the exception (accessible via Exception#message), and the third parameter is an array of callback information (accessible via Exception#backtrace). The cause of the generated exception (accessible via Exception#cause) is automatically set to the “current” exception ($!), if any. An alternative value, either an Exception object or nil, can be specified via the :cause argument.
Exceptions are caught by the rescue clause of begin...end blocks.
raise "Failed to create socket" raise ArgumentError, "No parameters", caller
Equivalent to method Kernel#gets, except that it raises an exception if called at end-of-stream:
$ cat t.txt | ruby -e "p readlines; readline" ["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"] in `readline': end of file reached (EOFError)
Optional keyword argument chomp specifies whether line separators are to be omitted.
Returns an array containing the lines returned by calling Kernel#gets until the end-of-stream is reached; (see Line IO).
With only string argument sep given, returns the remaining lines as determined by line separator sep, or nil if none; see Line Separator:
# Default separator. $ cat t.txt | ruby -e "p readlines" ["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"] # Specified separator. $ cat t.txt | ruby -e "p readlines 'li'" ["First li", "ne\nSecond li", "ne\n\nFourth li", "ne\nFifth li", "ne\n"] # Get-all separator. $ cat t.txt | ruby -e "p readlines nil" ["First line\nSecond line\n\nFourth line\nFifth line\n"] # Get-paragraph separator. $ cat t.txt | ruby -e "p readlines ''" ["First line\nSecond line\n\n", "Fourth line\nFifth line\n"]
With only integer argument limit given, limits the number of bytes in the line; see Line Limit:
$cat t.txt | ruby -e "p readlines 10" ["First line", "\n", "Second lin", "e\n", "\n", "Fourth lin", "e\n", "Fifth line", "\n"] $cat t.txt | ruby -e "p readlines 11" ["First line\n", "Second line", "\n", "\n", "Fourth line", "\n", "Fifth line\n"] $cat t.txt | ruby -e "p readlines 12" ["First line\n", "Second line\n", "\n", "Fourth line\n", "Fifth line\n"]
With arguments sep and limit given, combines the two behaviors; see Line Separator and Line Limit.
Optional keyword argument chomp specifies whether line separators are to be omitted:
$ cat t.txt | ruby -e "p readlines(chomp: true)" ["First line", "Second line", "", "Fourth line", "Fifth line"]
Optional keyword arguments enc_opts specify encoding options; see Encoding options.
Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference. clone copies the frozen value state of obj, unless the :freeze keyword argument is given with a false or true value. See also the discussion under Object#dup.
class Klass attr_accessor :str end s1 = Klass.new #=> #<Klass:0x401b3a38> s1.str = "Hello" #=> "Hello" s2 = s1.clone #=> #<Klass:0x401b3998 @str="Hello"> s2.str[1,4] = "i" #=> "i" s1.inspect #=> "#<Klass:0x401b3a38 @str=\"Hi\">" s2.inspect #=> "#<Klass:0x401b3998 @str=\"Hi\">"
This method may have class-specific behavior. If so, that behavior will be documented under the #initialize_copy method of the class.
Seeds the system pseudo-random number generator, with number. The previous seed value is returned.
If number is omitted, seeds the generator using a source of entropy provided by the operating system, if available (/dev/urandom on Unix systems or the RSA cryptographic provider on Windows), which is then combined with the time, the process id, and a sequence number.
srand may be used to ensure repeatable sequences of pseudo-random numbers between different runs of the program. By setting the seed to a known value, programs can be made deterministic during testing.
srand 1234 # => 268519324636777531569100071560086917274 [ rand, rand ] # => [0.1915194503788923, 0.6221087710398319] [ rand(10), rand(1000) ] # => [4, 664] srand 1234 # => 1234 [ rand, rand ] # => [0.1915194503788923, 0.6221087710398319]
If called without an argument, or if max.to_i.abs == 0, rand returns a pseudo-random floating point number between 0.0 and 1.0, including 0.0 and excluding 1.0.
rand #=> 0.2725926052826416
When max.abs is greater than or equal to 1, rand returns a pseudo-random integer greater than or equal to 0 and less than max.to_i.abs.
rand(100) #=> 12
When max is a Range, rand returns a random number where range.member?(number) == true.
Negative or floating point values for max are allowed, but may give surprising results.
rand(-100) # => 87 rand(-0.5) # => 0.8130921818028143 rand(1.9) # equivalent to rand(1), which is always 0
Kernel.srand may be used to ensure that sequences of random numbers are reproducible between different runs of a program.
See also Random.rand.
Returns x/y or arg as a Rational.
Rational(2, 3) #=> (2/3) Rational(5) #=> (5/1) Rational(0.5) #=> (1/2) Rational(0.3) #=> (5404319552844595/18014398509481984) Rational("2/3") #=> (2/3) Rational("0.3") #=> (3/10) Rational("10 cents") #=> ArgumentError Rational(nil) #=> TypeError Rational(1, nil) #=> TypeError Rational("10 cents", exception: false) #=> nil
Syntax of the string form:
string form = extra spaces , rational , extra spaces ;
rational = [ sign ] , unsigned rational ;
unsigned rational = numerator | numerator , "/" , denominator ;
numerator = integer part | fractional part | integer part , fractional part ;
denominator = digits ;
integer part = digits ;
fractional part = "." , digits , [ ( "e" | "E" ) , [ sign ] , digits ] ;
sign = "-" | "+" ;
digits = digit , { digit | "_" , digit } ;
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
extra spaces = ? \s* ? ;
See also String#to_r.
Specifies the handling of signals. The first parameter is a signal name (a string such as “SIGALRM”, “SIGUSR1”, and so on) or a signal number. The characters “SIG” may be omitted from the signal name. The command or block specifies code to be run when the signal is raised. If the command is the string “IGNORE” or “SIG_IGN”, the signal will be ignored. If the command is “DEFAULT” or “SIG_DFL”, the Ruby’s default handler will be invoked. If the command is “EXIT”, the script will be terminated by the signal. If the command is “SYSTEM_DEFAULT”, the operating system’s default handler will be invoked. Otherwise, the given command or block will be run. The special signal name “EXIT” or signal number zero will be invoked just prior to program termination. trap returns the previous handler for the given signal.
Signal.trap(0, proc { puts "Terminating: #{$$}" }) Signal.trap("CLD") { puts "Child died" } fork && Process.wait
produces:
Terminating: 27461 Child died Terminating: 27460
Deprecated. Use block_given? instead.
If warnings have been disabled (for example with the -W0 flag), does nothing. Otherwise, converts each of the messages to strings, appends a newline character to the string if the string does not end in a newline, and calls Warning.warn with the string.
warn("warning 1", "warning 2")
<em>produces:</em>
warning 1
warning 2
If the uplevel keyword argument is given, the string will be prepended with information for the given caller frame in the same format used by the rb_warn C function.
# In baz.rb
def foo
warn("invalid call to foo", uplevel: 1)
end
def bar
foo
end
bar
<em>produces:</em>
baz.rb:6: warning: invalid call to foo
If category keyword argument is given, passes the category to Warning.warn. The category given must be be one of the following categories:
Used for warning for deprecated functionality that may be removed in the future.
Used for experimental features that may change in future releases.
With a block given, returns an array of two arrays:
The first having those elements for which the block returns a truthy value.
The other having all other elements.
Examples:
p = (1..4).partition {|i| i.even? } p # => [[2, 4], [1, 3]] p = ('a'..'d').partition {|c| c < 'c' } p # => [["a", "b"], ["c", "d"]] h = {foo: 0, bar: 1, baz: 2, bat: 3} p = h.partition {|key, value| key.start_with?('b') } p # => [[[:bar, 1], [:baz, 2], [:bat, 3]], [[:foo, 0]]] p = h.partition {|key, value| value < 2 } p # => [[[:foo, 0], [:bar, 1]], [[:baz, 2], [:bat, 3]]]
With no block given, returns an Enumerator.
Related: Enumerable#group_by.