Project

General

Profile

Actions

Feature #8842

closed

Integer#[] with range

Added by mame (Yusuke Endoh) over 8 years ago. Updated about 3 years ago.

Status:
Closed
Priority:
Normal
Target version:
-
[ruby-core:56902]

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


Files

integer-with-range.pdf (248 KB) integer-with-range.pdf mame (Yusuke Endoh), 08/31/2013 11:47 AM
Actions

Also available in: Atom PDF