Feature #15813: Proposal: Add exception support in `Range#first`

• Status: Closed
• Assignee: -
• Target version: -

[osyo (manga osyo)]

Current status

Calling Range#last in endless range((1..)) raises an exception.

# OK
p (1..Float::INFINITY).end   # => Infinity
p (1..).end                  # => nil
p (1..Float::INFINITY).last  # => Infinity

# NG: Raise error: in `last': cannot get the last element of endless range (RangeError)
p (1..).last
p (1..).last(1)

But, calling Range#first in beginless range((..1)) does not raise an exception.

# OK
p (-Float::INFINITY..1).begin  # => -Infinity
p (..1).begin                  # => nil
p (-Float::INFINITY..1).first  # => -Infinity

# OK: Does not raise
p (..1).first   # => nil

# NG: Raise error: in `each': can't iterate from NilClass (TypeError)
p (..1).first(1)

I think the current situation is not consistent, so it is necessary to move the behavior to one side or the other.
Also, in the case of Range#last, an exception is explicitly raised.
see: https://github.com/ruby/ruby/blob/6a3165e19dfa21babfb2ef1f1c20c9930410b0ec/range.c#L1100-L1102

Proposal

Added support to raise an exception for Range#first too.

Before

# OK
p (-Float::INFINITY..10).begin  # => -Infinity
p (..10).begin                  # => nil
p (-Float::INFINITY..10).first  # => -Infinity
p (..10).first                  # => nil
p Range.new(nil, 10).first      # => nil

# NG: Raise error: in `each': can't iterate from NilClass (TypeError)
p (..10).first(1)

After

# OK
p (-Float::INFINITY..10).begin  # => -Infinity
p (..10).begin                  # => nil
p (-Float::INFINITY..10).first  # => -Infinity

# NG: Raise error: in `first': cannot get the first element of beginless range (RangeError)
p (..10).first
p Range.new(nil, 10).first
p (..10).first(1)

# in Ruby 2.6.1
p Range.new(nil, 10).first
# Error: in `initialize': bad value for range (ArgumentError)

Thank you.

pull request : https://github.com/ruby/ruby/pull/2163

[mame (Yusuke Endoh)]

Merged at 4e88e8692844a2a317bc19481f0f2601b6f00955. Thank you.

[mame (Yusuke Endoh)]

• Status changed from Open to Closed

[osyo (manga osyo)]

Thanks!!!!!!!