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Feature #8842
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Integer#[] with range
Description
=begin
I propose to extend Integer#[] accepting a range.
0b01001101[2, 4] == 0b0011
0bHGFEDCBA[2, 4] == 0bFEDC
== Use case
I believe that everyone has written a code like this:
if (n >> 2) & 0xf == 0x3
...
end
because this is a very common idiom in C.
But it is less readable, writable, extendable and optimizable.
if n[2, 4] == 0x3
...
end
is much better in the all aspects.
== Corner cases
The current Integer#[] (and shift operators) handle an integer as "a bit array with infinity length";
it returns 0 for any negative index and an (extended) sign bit for any index greater than MSB.
We also can use this standard to define the spec for a range argument.
For example:
15[-1, 42] #=> 30 (equivalent to (15 << 1) && (2 ** 42 - 1))
15[3, 42] #=> 1 (equivalent to (15 >> 3) && (2 ** 42 - 1))
15[3..Float::INFINITY] #=> 1 (equivalent to 15 >> 3)
15[-3..Float::INFINITY] #=> 2 (equivalent to 1 << 3)
-1[0..Float::INFINITY] #=> -1
-1[1..Float::INFINITY] #=> -1
-1[-1..Float::INFINITY] #=> -2
1[-Float::INFINITY..0] #=> failed to allocate memory
2[-Float::INFINITY..0] #=> 0
Only tricky case that I thought of is a range (beg..end) whose "end" is smaller than "beg".
I think it should be handled as (beg..Float::INFINITY).
15[-3..-4] #=> 2 (equivalent to 1 << 3)
-1[0..-1] #=> -1
-1[0..-2] #=> -1
What do you think?
=end
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