Set default random arg to nil instead of Random::DEFAULT

src/array.cr

@@ -1604,9 +1604,10 @@ class Array(T)
     shift { nil }
   end
 
-  # Returns an array with all the elements in the collection randomized
-  # using the given *random* number generator.
-  def shuffle(random : Random = Random::DEFAULT) : Array(T)
+  # Returns a new instance with all elements in the collection randomized.
+  #
+  # See `Indexable::Mutable#shuffle!` for details.
+  def shuffle(random : Random? = nil) : Array(T)
     dup.shuffle!(random)
   end
 

src/crystal/system/file.cr

@@ -51,7 +51,7 @@ module Crystal::System::File
 
   LOWER_ALPHANUM = "0123456789abcdefghijklmnopqrstuvwxyz".to_slice
 
-  def self.mktemp(prefix : String?, suffix : String?, dir : String, random : ::Random = ::Random::DEFAULT) : {FileDescriptor::Handle, String, Bool}
+  def self.mktemp(prefix : String?, suffix : String?, dir : String, random : ::Random? = nil) : {FileDescriptor::Handle, String, Bool}
     flags = LibC::O_RDWR | LibC::O_CREAT | LibC::O_EXCL
     perm = ::File::Permissions.new(0o600)
 

src/enumerable.cr

@@ -1565,19 +1565,27 @@ module Enumerable(T)
     reject { |e| pattern === e }
   end
 
-  # Returns an `Array` of *n* random elements from `self`, using the given
-  # *random* number generator. All elements have equal probability of being
-  # drawn. Sampling is done without replacement; if *n* is larger than the size
-  # of this collection, the returned `Array` has the same size as `self`.
+  # Returns an `Array` of *n* random elements from `self`. All elements have
+  # equal probability of being drawn. Sampling is done without replacement; if
+  # *n* is larger than the size of this collection, the returned `Array` has the
+  # same size as `self`.
   #
   # Raises `ArgumentError` if *n* is negative.
   #
   # ```
-  # [1, 2, 3, 4, 5].sample(2)                # => [3, 5]
-  # {1, 2, 3, 4, 5}.sample(2)                # => [3, 4]
-  # {1, 2, 3, 4, 5}.sample(2, Random.new(1)) # => [1, 5]
+  # [1, 2, 3, 4, 5].sample(2) # => [3, 5]
+  # {1, 2, 3, 4, 5}.sample(2) # => [3, 4]
   # ```
-  def sample(n : Int, random : Random = Random::DEFAULT) : Array(T)
+  #
+  # Uses the *random* instance when provided if the randomness needs to be
+  # controlled or to follow some traits. For example the following calls use a
+  # custom seed or a secure random source:
+  #
+  # ```
+  # {1, 2, 3, 4, 5}.sample(2, Random.new(1))  # => [1, 5]
+  # {1, 2, 3, 4, 5}.sample(2, Random::Secure) # => [2, 5]
+  # ```
+  def sample(n : Int, random : Random? = nil) : Array(T)
     raise ArgumentError.new("Can't sample negative number of elements") if n < 0
 
     # Unweighted reservoir sampling:
@@ -1588,40 +1596,54 @@ module Enumerable(T)
     ary = Array(T).new(n)
     return ary if n == 0
 
+    # FIXME: thread unsafe (#each may yield and the fiber switch threads)
+    rng = random || Random::DEFAULT
+
     each_with_index do |elem, i|
       if i < n
         ary << elem
       else
-        j = random.rand(i + 1)
+        j = rng.rand(i + 1)
         if j < n
           ary.to_unsafe[j] = elem
         end
       end
     end
 
-    ary.shuffle!(random)
+    ary.shuffle!(rng)
   end
 
-  # Returns a random element from `self`, using the given *random* number
-  # generator. All elements have equal probability of being drawn.
+  # Returns a random element from `self`. All elements have equal probability of
+  # being drawn.
   #
   # Raises `IndexError` if `self` is empty.
   #
   # ```
   # a = [1, 2, 3]
-  # a.sample                # => 2
-  # a.sample                # => 1
-  # a.sample(Random.new(1)) # => 3
+  # a.sample # => 2
+  # a.sample # => 1
   # ```
-  def sample(random : Random = Random::DEFAULT) : T
+  #
+  # Uses the *random* instance when provided if the randomness needs to be
+  # controlled or to follow some traits. For example the following calls use a
+  # custom seed or a secure random source:
+  #
+  # ```
+  # a.sample(Random.new(1))  # => 3
+  # a.sample(Random::Secure) # => 1
+  # ```
+  def sample(random : Random? = nil) : T
     value = uninitialized T
     found = false
 
+    # FIXME: thread unsafe (#each may yield and the fiber switch threads)
+    rng = random || Random::DEFAULT
+
     each_with_index do |elem, i|
       if !found
         value = elem
         found = true
-      elsif random.rand(i + 1) == 0
+      elsif rng.rand(i + 1) == 0
         value = elem
       end
     end

src/indexable.cr

@@ -950,21 +950,31 @@ module Indexable(T)
   #
   # ```
   # a = [1, 2, 3]
-  # a.sample                # => 3
-  # a.sample                # => 1
+  # a.sample # => 3
+  # a.sample # => 1
+  # ```
+  #
+  # Uses the *random* instance when provided if the randomness needs to be
+  # controlled or to follow some traits. For example the following sample will
+  # always return the same value:
+  #
+  # ```
+  # a = [1, 2, 3]
+  # a.sample(Random.new(1)) # => 2
   # a.sample(Random.new(1)) # => 2
   # ```
-  def sample(random : Random = Random::DEFAULT)
+  def sample(random : Random? = nil)
     raise IndexError.new("Can't sample empty collection") if size == 0
-    unsafe_fetch(random.rand(size))
+    rng = random || Random::DEFAULT
+    unsafe_fetch(rng.rand(size))
   end
 
   # :inherit:
   #
   # If `self` is not empty and `n` is equal to 1, calls `sample(random)` exactly
   # once. Thus, *random* will be left in a different state compared to the
   # implementation in `Enumerable`.
-  def sample(n : Int, random : Random = Random::DEFAULT) : Array(T)
+  def sample(n : Int, random : Random? = nil) : Array(T)
     return super unless n == 1
 
     if empty?

src/indexable/mutable.cr

@@ -251,17 +251,29 @@ module Indexable::Mutable(T)
     self
   end
 
-  # Modifies `self` by randomizing the order of elements in the collection
-  # using the given *random* number generator. Returns `self`.
+  # Modifies `self` by randomizing the order of elements in the collection.
+  # Returns `self`.
   #
   # ```
   # a = [1, 2, 3, 4, 5]
+  # a.shuffle! # => [3, 5, 2, 4, 1]
+  # a          # => [3, 5, 2, 4, 1]
+  # ```
+  #
+  # Uses the *random* instance when provided if the randomness needs to be
+  # controlled or to follow some traits. For example the following shuffle will
+  # always result in the same order:
+  #
+  # ```
+  # a = [1, 2, 3, 4, 5]
+  # a.shuffle!(Random.new(42)) # => [3, 2, 4, 5, 1]
   # a.shuffle!(Random.new(42)) # => [3, 2, 4, 5, 1]
   # a                          # => [3, 2, 4, 5, 1]
   # ```
-  def shuffle!(random : Random = Random::DEFAULT) : self
+  def shuffle!(random : Random? = nil) : self
+    rng = random || Random::DEFAULT
     (size - 1).downto(1) do |i|
-      j = random.rand(i + 1)
+      j = rng.rand(i + 1)
       swap(i, j)
     end
     self

src/pointer.cr

@@ -382,9 +382,10 @@ struct Pointer(T)
   # ptr.shuffle!(4)
   # ptr # [3, 4, 1, 2]
   # ```
-  def shuffle!(count : Int, random = Random::DEFAULT)
+  def shuffle!(count : Int, random : Random? = nil)
+    rng = random || Random::DEFAULT
     (count - 1).downto(1) do |i|
-      j = random.rand(i + 1)
+      j = rng.rand(i + 1)
       swap(i, j)
     end
     self

src/range.cr

@@ -344,11 +344,13 @@ struct Range(B, E)
   # the method simply calls `random.rand(self)`.
   #
   # Raises `ArgumentError` if `self` is an open range.
-  def sample(random : Random = Random::DEFAULT)
+  def sample(random : Random? = nil)
+    rng = random || Random::DEFAULT
+
     {% if B < Int && E < Int %}
-      random.rand(self)
+      rng.rand(self)
     {% elsif B < Float && E < Float %}
-      random.rand(self)
+      rng.rand(self)
     {% elsif B.nilable? || E.nilable? %}
       b = self.begin
       e = self.end
@@ -357,7 +359,7 @@ struct Range(B, E)
         raise ArgumentError.new("Can't sample an open range")
       end
 
-      Range.new(b, e, @exclusive).sample(random)
+      Range.new(b, e, @exclusive).sample(rng)
     {% else %}
       super
     {% end %}
@@ -368,7 +370,9 @@ struct Range(B, E)
   # If `self` is not empty and `n` is equal to 1, calls `sample(random)` exactly
   # once. Thus, *random* will be left in a different state compared to the
   # implementation in `Enumerable`.
-  def sample(n : Int, random = Random::DEFAULT)
+  def sample(n : Int, random : Random? = nil)
+    rng = random || Random::DEFAULT
+
     if self.begin.nil? || self.end.nil?
       raise ArgumentError.new("Can't sample an open range")
     end
@@ -402,11 +406,11 @@ struct Range(B, E)
       # If we must return all values in the range...
       if possible == available
         result = Array(B).new(possible) { |i| min + i }
-        result.shuffle!(random)
+        result.shuffle!(rng)
         return result
       end
 
-      range_sample(n, random)
+      range_sample(n, rng)
     {% elsif B < Float && E < Float %}
       min = self.begin
       max = self.end
@@ -419,13 +423,13 @@ struct Range(B, E)
         return [min]
       end
 
-      range_sample(n, random)
+      range_sample(n, rng)
     {% else %}
       case n
       when 0
         [] of B
       when 1
-        [sample(random)]
+        [sample(rng)]
       else
         super
       end

src/slice.cr

@@ -358,7 +358,7 @@ struct Slice(T)
   # :inherit:
   #
   # Raises if this slice is read-only.
-  def shuffle!(random : Random = Random::DEFAULT) : self
+  def shuffle!(random : Random? = nil) : self
     check_writable
     super
   end