Class

`Random`

provides an interface to Ruby's pseudo-random number generator, or PRNG. The PRNG produces a deterministic sequence of bits which approximate true randomness. The sequence may be represented by integers, floats, or binary strings.

The generator may be initialized with either a system-generated or user-supplied seed value by using `Random.srand`

.

The class method `Random.rand`

provides the base functionality of `Kernel.rand`

along with better handling of floating point values. These are both interfaces to `Random::DEFAULT`

, the Ruby system PRNG.

`Random.new`

will create a new PRNG with a state independent of `Random::DEFAULT`

, allowing multiple generators with different seed values or sequence positions to exist simultaneously. `Random`

objects can be marshaled, allowing sequences to be saved and resumed.

PRNGs are currently implemented as a modified Mersenne Twister with a period of 2**19937-1.

Returns true if the two generators have the same internal state, otherwise false. Equivalent generators will return the same sequence of pseudo-random numbers. Two generators will generally have the same state only if they were initialized with the same seed

Random.new == Random.new # => false Random.new(1234) == Random.new(1234) # => true

and have the same invocation history.

prng1 = Random.new(1234) prng2 = Random.new(1234) prng1 == prng2 # => true prng1.rand # => 0.1915194503788923 prng1 == prng2 # => false prng2.rand # => 0.1915194503788923 prng1 == prng2 # => true

Returns a random binary string containing `size`

bytes.

random_string = Random.new.bytes(10) # => "\xD7:R\xAB?\x83\xCE\xFAkO" random_string.size # => 10

Creates a new PRNG using `seed`

to set the initial state. If `seed`

is omitted, the generator is initialized with `Random.new_seed`

.

See `Random.srand`

for more information on the use of seed values.

Returns an arbitrary seed value. This is used by `Random.new`

when no seed value is specified as an argument.

Random.new_seed #=> 115032730400174366788466674494640623225

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 `max`

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`

.

Returns the seed value used to initialize the generator. This may be used to initialize another generator with the same state at a later time, causing it to produce the same sequence of numbers.

prng1 = Random.new(1234) prng1.seed #=> 1234 prng1.rand(100) #=> 47 prng2 = Random.new(prng1.seed) prng2.rand(100) #=> 47

Seeds the system pseudo-random number generator, `Random::DEFAULT`

, 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"