Ruby

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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?
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