module Comparable

The Comparable mixin is used by classes whose objects may be ordered. The class must define the <=> operator, which compares the receiver against another object, returning a value less than 0, returning 0, or returning a value greater than 0, depending on whether the receiver is less than, equal to, or greater than the other object. If the other object is not comparable then the <=> operator should return nil. Comparable uses <=> to implement the conventional comparison operators (<, <=, ==, >=, and >) and the method between?.

class StringSorter
  include Comparable

  attr :str
  def <=>(other)
    str.size <=> other.str.size
  end

  def initialize(str)
    @str = str
  end

  def inspect
    @str
  end
end

s1 = StringSorter.new("Z")
s2 = StringSorter.new("YY")
s3 = StringSorter.new("XXX")
s4 = StringSorter.new("WWWW")
s5 = StringSorter.new("VVVVV")

s1 < s2                       #=> true
s4.between?(s1, s3)           #=> false
s4.between?(s3, s5)           #=> true
[ s3, s2, s5, s4, s1 ].sort   #=> [Z, YY, XXX, WWWW, VVVVV]

What’s Here ↑

Module Comparable provides these methods, all of which use method #<=>:

Public Instance Methods

obj < other → true or false

Compares two objects based on the receiver’s <=> method, returning true if it returns a value less than 0.

static VALUE
cmp_lt(VALUE x, VALUE y)
{
    return RBOOL(cmpint(x, y) < 0);
}
obj <= other → true or false

Compares two objects based on the receiver’s <=> method, returning true if it returns a value less than or equal to 0.

static VALUE
cmp_le(VALUE x, VALUE y)
{
    return RBOOL(cmpint(x, y) <= 0);
}
obj == other → true or false

Compares two objects based on the receiver’s <=> method, returning true if it returns 0. Also returns true if obj and other are the same object.

static VALUE
cmp_equal(VALUE x, VALUE y)
{
    VALUE c;
    if (x == y) return Qtrue;

    c = rb_exec_recursive_paired_outer(cmp_eq_recursive, x, y, y);

    if (NIL_P(c)) return Qfalse;
    return RBOOL(rb_cmpint(c, x, y) == 0);
}
obj > other → true or false

Compares two objects based on the receiver’s <=> method, returning true if it returns a value greater than 0.

static VALUE
cmp_gt(VALUE x, VALUE y)
{
    return RBOOL(cmpint(x, y) > 0);
}
obj >= other → true or false

Compares two objects based on the receiver’s <=> method, returning true if it returns a value greater than or equal to 0.

static VALUE
cmp_ge(VALUE x, VALUE y)
{
    return RBOOL(cmpint(x, y) >= 0);
}
between?(min, max) → true or false

Returns false if obj <=> min is less than zero or if obj <=> max is greater than zero, true otherwise.

3.between?(1, 5)               #=> true
6.between?(1, 5)               #=> false
'cat'.between?('ant', 'dog')   #=> true
'gnu'.between?('ant', 'dog')   #=> false

static VALUE
cmp_between(VALUE x, VALUE min, VALUE max)
{
    return RBOOL((cmpint(x, min) >= 0 && cmpint(x, max) <= 0));
}
clamp(min, max) → obj
clamp(range) → obj

In (min, max) form, returns min if obj <=> min is less than zero, max if obj <=> max is greater than zero, and obj otherwise.

12.clamp(0, 100)         #=> 12
523.clamp(0, 100)        #=> 100
-3.123.clamp(0, 100)     #=> 0

'd'.clamp('a', 'f')      #=> 'd'
'z'.clamp('a', 'f')      #=> 'f'

If min is nil, it is considered smaller than obj, and if max is nil, it is considered greater than obj.

-20.clamp(0, nil)           #=> 0
523.clamp(nil, 100)         #=> 100

In (range) form, returns range.begin if obj <=> range.begin is less than zero, range.end if obj <=> range.end is greater than zero, and obj otherwise.

12.clamp(0..100)         #=> 12
523.clamp(0..100)        #=> 100
-3.123.clamp(0..100)     #=> 0

'd'.clamp('a'..'f')      #=> 'd'
'z'.clamp('a'..'f')      #=> 'f'

If range.begin is nil, it is considered smaller than obj, and if range.end is nil, it is considered greater than obj.

-20.clamp(0..)           #=> 0
523.clamp(..100)         #=> 100

When range.end is excluded and not nil, an exception is raised.

100.clamp(0...100)       # ArgumentError

static VALUE
cmp_clamp(int argc, VALUE *argv, VALUE x)
{
    VALUE min, max;
    int c, excl = 0;

    if (rb_scan_args(argc, argv, "11", &min, &max) == 1) {
        VALUE range = min;
        if (!rb_range_values(range, &min, &max, &excl)) {
            rb_raise(rb_eTypeError, "wrong argument type %s (expected Range)",
                     rb_builtin_class_name(range));
        }
        if (!NIL_P(max)) {
            if (excl) rb_raise(rb_eArgError, "cannot clamp with an exclusive range");
        }
    }
    if (!NIL_P(min) && !NIL_P(max) && cmpint(min, max) > 0) {
        rb_raise(rb_eArgError, "min argument must be less than or equal to max argument");
    }

    if (!NIL_P(min)) {
        c = cmpint(x, min);
        if (c == 0) return x;
        if (c < 0) return min;
    }
    if (!NIL_P(max)) {
        c = cmpint(x, max);
        if (c > 0) return max;
    }
    return x;
}