Project

General

Profile

Feature #17056

Array#index: Allow specifying the position to start search as in String#index

Added by TylerRick (Tyler Rick) 8 days ago. Updated 6 days ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:99380]

Description

I have a use case of finding the first matching line within a given section in a file. After finding the line number of the start of the section, I want to find the first match after that line.

My workaround for now is to use with_index:

lines = pathname.read.lines
section_start_line = lines.index {|line| line.start_with?(/#* #{section_name}/) }
lines.index.with_index {|line, i| i > section_start_line && line.include?(sought) }

I'd like to do it in a more concise way using a feature of Array#index that I propose here, which is analogous to String#index.

If the second parameter of String#index is present, it specifies the position in the string to begin the search:

'abcabc'.index('a') # => 0
'abcabc'.index('a',2) # => 3

I would expect to also be able to do:

'abcabc'.chars.index('a') # => 0
'abcabc'.chars.index('a', 2)

Using such feature, I would be able to do:

lines.index(sought, section_start_line)

This would give Ruby better parity with other programming languages like Python:

>>> list('abcabc')
['a', 'b', 'c', 'a', 'b', 'c']
>>> list('abcabc').index('a')
0
>>> list('abcabc').index('a', 2)
3

End index

We can further think of an optional parameter to specify the position to end the search. The following languages allow specifying both start and end indexes:

Ruby's String#index does not have one, so we could make a separate proposal to add end to both methods at the same time.

#1

Updated by TylerRick (Tyler Rick) 8 days ago

  • Description updated (diff)
#2

Updated by TylerRick (Tyler Rick) 8 days ago

  • Description updated (diff)
#3

Updated by sawa (Tsuyoshi Sawada) 6 days ago

  • Description updated (diff)
  • Subject changed from Array#index: Allow specifying start index to search like String#index does to Array#index: Allow specifying the position to start search as in String#index

Also available in: Atom PDF