module Comparable - RDoc Documentation

# 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 SizeMatters
      include Comparable
      attr :str
      def <=>(other)
        str.size <=> other.str.size
      end
      def initialize(str)
        @str = str
      end
      def inspect
        @str
      end
    end

    s1 = SizeMatters.new("Z")
    s2 = SizeMatters.new("YY")
    s3 = SizeMatters.new("XXX")
    s4 = SizeMatters.new("WWWW")
    s5 = SizeMatters.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 `<=>`:

- <

    Returns whether `self` is less than the given object.

- <=

    Returns whether `self` is less than or equal to the given object.

- ==

    Returns whether `self` is equal to the given object.

- >

    Returns whether `self` is greater than or equal to the given object.

- >=

    Returns whether `self` is greater than the given object.

- `between?` Returns `true` if `self` is between two given objects.

- `clamp`

    For given objects `min` and `max`, or range `(min..max)`, returns:

  - `min` if `(self <=> min) < 0`.

  - `max` if `(self <=> max) > 0`.

  - `self` otherwise.

### Public Instance Methods

obj < other → true or false click to toggle source

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 click to toggle source

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 click to toggle source

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 click to toggle source

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 click to toggle source

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 click to toggle source

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)
    {
        if (cmpint(x, min) < 0) return Qfalse;
        if (cmpint(x, max) > 0) return Qfalse;
        return Qtrue;
    }

clamp(min, max) → obj click to toggle source
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'

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 smaller than 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;
    }