Controls tracing of assignments to global variables. The parameter symbol identifies the variable (as either a string name or a symbol identifier). cmd (which may be a string or a Proc object) or block is executed whenever the variable is assigned. The block or Proc object receives the variable’s new value as a parameter. Also see untrace_var.
trace_var :$_, proc {|v| puts "$_ is now '#{v}'" } $_ = "hello" $_ = ' there'
produces:
$_ is now 'hello' $_ is now ' there'
Removes tracing for the specified command on the given global variable and returns nil. If no command is specified, removes all tracing for that variable and returns an array containing the commands actually removed.
Converts block to a Proc object (and therefore binds it at the point of call) and registers it for execution when the program exits. If multiple handlers are registered, they are executed in reverse order of registration.
def do_at_exit(str1) at_exit { print str1 } end at_exit { puts "cruel world" } do_at_exit("goodbye ") exit
produces:
goodbye cruel world
Returns the names of the current local variables.
fred = 1 for i in 1..10 # ... end local_variables #=> [:fred, :i]
With a block given, returns an array of elements of self, sorted according to the value returned by the block for each element. The ordering of equal elements is indeterminate and may be unstable.
Examples:
a = %w[xx xxx x xxxx] a.sort_by {|s| s.size } # => ["x", "xx", "xxx", "xxxx"] a.sort_by {|s| -s.size } # => ["xxxx", "xxx", "xx", "x"] h = {foo: 2, bar: 1, baz: 0} h.sort_by{|key, value| value } # => [[:baz, 0], [:bar, 1], [:foo, 2]] h.sort_by{|key, value| key } # => [[:bar, 1], [:baz, 0], [:foo, 2]]
With no block given, returns an Enumerator.
The current implementation of sort_by generates an array of tuples containing the original collection element and the mapped value. This makes sort_by fairly expensive when the keysets are simple.
require 'benchmark' a = (1..100000).map { rand(100000) } Benchmark.bm(10) do |b| b.report("Sort") { a.sort } b.report("Sort by") { a.sort_by { |a| a } } end
produces:
user system total real Sort 0.180000 0.000000 0.180000 ( 0.175469) Sort by 1.980000 0.040000 2.020000 ( 2.013586)
However, consider the case where comparing the keys is a non-trivial operation. The following code sorts some files on modification time using the basic sort method.
files = Dir["*"] sorted = files.sort { |a, b| File.new(a).mtime <=> File.new(b).mtime } sorted #=> ["mon", "tues", "wed", "thurs"]
This sort is inefficient: it generates two new File objects during every comparison. A slightly better technique is to use the Kernel#test method to generate the modification times directly.
files = Dir["*"] sorted = files.sort { |a, b| test(?M, a) <=> test(?M, b) } sorted #=> ["mon", "tues", "wed", "thurs"]
This still generates many unnecessary Time objects. A more efficient technique is to cache the sort keys (modification times in this case) before the sort. Perl users often call this approach a Schwartzian transform, after Randal Schwartz. We construct a temporary array, where each element is an array containing our sort key along with the filename. We sort this array, and then extract the filename from the result.
sorted = Dir["*"].collect { |f| [test(?M, f), f] }.sort.collect { |f| f[1] } sorted #=> ["mon", "tues", "wed", "thurs"]
This is exactly what sort_by does internally.
sorted = Dir["*"].sort_by { |f| test(?M, f) } sorted #=> ["mon", "tues", "wed", "thurs"]
To produce the reverse of a specific order, the following can be used:
ary.sort_by { ... }.reverse!
Returns an array of flattened objects returned by the block.
With a block given, calls the block with successive elements; returns a flattened array of objects returned by the block:
[0, 1, 2, 3].flat_map {|element| -element } # => [0, -1, -2, -3] [0, 1, 2, 3].flat_map {|element| [element, -element] } # => [0, 0, 1, -1, 2, -2, 3, -3] [[0, 1], [2, 3]].flat_map {|e| e + [100] } # => [0, 1, 100, 2, 3, 100] {foo: 0, bar: 1, baz: 2}.flat_map {|key, value| [key, value] } # => [:foo, 0, :bar, 1, :baz, 2]
With no block given, returns an Enumerator.
Alias: collect_concat.
Calls the block with each successive overlapped n-tuple of elements; returns self:
a = [] (1..5).each_cons(3) {|element| a.push(element) } a # => [[1, 2, 3], [2, 3, 4], [3, 4, 5]] a = [] h = {foo: 0, bar: 1, baz: 2, bam: 3} h.each_cons(2) {|element| a.push(element) } a # => [[[:foo, 0], [:bar, 1]], [[:bar, 1], [:baz, 2]], [[:baz, 2], [:bam, 3]]]
With no block given, returns an Enumerator.
Enters exclusive section.
Returns true if this monitor is locked by any thread
Returns true if this monitor is locked by current thread.
Creates a new MonitorMixin::ConditionVariable associated with the Monitor object.
Alias of GC.start
Alias of GC.start
Dump Ruby object to a JSON string.
Returns true if the named file is writable by the real user and group id of this process. See access(3).
Note that some OS-level security features may cause this to return true even though the file is not writable by the real user/group.
If file_name is writable by others, returns an integer representing the file permission bits of file_name. Returns nil otherwise. The meaning of the bits is platform dependent; on Unix systems, see stat(2).
file_name can be an IO object.
File.world_writable?("/tmp") #=> 511 m = File.world_writable?("/tmp") sprintf("%o", m) #=> "777"
Alias of GC.start
Find the full path to the executable for gem name. If the exec_name is not given, an exception will be raised, otherwise the specified executable’s path is returned. requirements allows you to specify specific gem versions.
The mode needed to read a file as straight binary.
Adds a post-installs hook that will be passed a Gem::DependencyInstaller and a list of installed specifications when Gem::DependencyInstaller#install is complete
Safely read a file in binary mode on all platforms.
Glob pattern for require-able path suffixes.
Use the home and paths values for Gem.dir and Gem.path. Used mainly by the unit tests to provide environment isolation.
Is this platform Solaris?
The path to standard location of the user’s configuration directory.