Bug #12090: `Range#cover` does not raise an exception when comparison fails

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN

[sawa (Tsuyoshi Sawada)]

The documentation for Range#cover? says,

cover?(obj) → true or false

Returns true if obj is between the begin and end of the range.

This tests begin <= obj <= end when exclude_end? is false and begin <= obj < end when exclude_end? is true.

which implies that, when comparison fails, cover? should raise an error. But actually, it doesn't:

"a" <= 1 # => ArgumentError: comparison of String with 1 failed
1 <= "a" # => ArgumentError: comparison of Fixnum with String failed
("a".."z").cover?(1) # => false

It silently returns false instead of raising an error.

Either Range#cover? should raise an error when comparison fails, or the documentation should be changed to correctly describe this behaviour.

[sos4nt (Stefan Schüßler)]

Raising an error would break backward compatibility. Maybe cover? should just return nil to indicate incomparable values.

("a".."z").cover?("c")  # => true
("a".."z").cover?("5")  # => false
("a".."z").cover?(1)    # => nil

• Status changed from Open to Closed

Applied in changeset git|3556cba5038530e728eb6309dcf5d4d1a96a02ac.

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Document that Range#cover? returns false if <=> returns nil

Fixes [Bug #12090]