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partial_comparable.cr
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partial_comparable.cr
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# The `PartialComparable` mixin is used by classes whose objects may be partially ordered.
#
# Including types must provide an `<=>` method, which compares the receiver against
# another object, returning `-1`, `0`, `+1` or `nil` depending on whether
# the receiver is less than, equal to, greater than the other object,
# or no order can be established.
#
# `PartialComparable` uses `<=>` to implement the conventional
# comparison operators (`<`, `<=`, `==`, `>=`, and `>`).
module PartialComparable(T)
# Compares this object to *other* based on the receiver’s `<=>` method,
# returning `true` if it returns `-1`.
def <(other : T)
compare_with(other) do |cmp|
cmp < 0
end
end
# Compares this object to *other* based on the receiver’s `<=>` method,
# returning `true` if it returns `-1` or `0`.
def <=(other : T)
compare_with(other) do |cmp|
cmp <= 0
end
end
# Compares this object to *other* based on the receiver’s `<=>` method,
# returning `true` if it returns `0`.
# Also returns `true` if this and *other* are the same object.
def ==(other : T)
if self.is_a?(Reference) && (other.is_a?(Reference) || other.is_a?(Nil))
return true if self.same?(other)
end
compare_with(other) do |cmp|
cmp == 0
end
end
# Compares this object to *other* based on the receiver’s `<=>` method,
# returning `true` if it returns `1`.
def >(other : T)
compare_with(other) do |cmp|
cmp > 0
end
end
# Compares this object to *other* based on the receiver’s `<=>` method,
# returning `true` if it returns `1` or `0`.
def >=(other : T)
compare_with(other) do |cmp|
cmp >= 0
end
end
def compare_with(other : T)
cmp = self <=> other
if cmp
yield cmp
else
false
end
end
abstract def <=>(other : T)
end