Feature #8811
closedCounterpart to `Hash#key?` for `Array`
Description
=begin
Hash
hash key?
to tell if a key exists without checking the value. It would be convenient if there were a counterpart in Array
. Suppose it is called Array#index?
. Then it should behave as follows:
[1, 2, 3].index?(2) # => true
[1, 2, 3].index?(3) # => false
[1, 2, 3].index?(-3) # => true
[1, 2, 3].index?(-4) # => false
This is useful when we want to insert/move/delete elements to/from a certain position of an array. Without checking if a value exists, it can be messed up. Implementing a check is cumbersome now. With the proposed method, it would become easy.
=end
Files
Updated by matz (Yukihiro Matsumoto) over 10 years ago
- Status changed from Open to Feedback
Concrete use-case please? Besides that, I don't think #index? is a good name for the function.
Matz.
Updated by phluid61 (Matthew Kerwin) over 10 years ago
- File rb_ary_has_index.patch rb_ary_has_index.patch added
matz (Yukihiro Matsumoto) wrote:
Concrete use-case please? Besides that, I don't think #index? is a good name for the function.
Matz.
I think the name is reasonable. Hash defines:
- #key(value) => key of value
- #key?(key) => true if key present
- #has_key?(key) => alias of #key?
Array defines:
- #index(value) => index of value
It makes sense that this method would be called #index? and/or #has_index?
Updated by alexeymuranov (Alexey Muranov) over 10 years ago
phluid61 (Matthew Kerwin) wrote:
matz (Yukihiro Matsumoto) wrote:
Concrete use-case please? Besides that, I don't think #index? is a good name for the function.
Matz.
I think the name is reasonable. Hash defines:
- #key(value) => key of value
- #key?(key) => true if key present
- #has_key?(key) => alias of #key?
Array defines:
- #index(value) => index of value
It makes sense that this method would be called #index? and/or #has_index?
There are two ways of using #index with an array: with non-negaitve integers, and with negaitve integers. It does not seem to make much sense to have an #index? method that returns true whenever an index fits one or the other convention. It seems to me indeed hard to come up with a use-case where the user wants to know if a number can be used as an index, but does not care if it is negative or positive. Two separate methods like #non_negative_index? and #negative_index? would look more natural but cumbersome to me.
Updated by zzak (zzak _) over 10 years ago
Shouldn't it be called Hash#value then?
Updated by zzak (zzak _) over 10 years ago
Ahh, sorry I misunderstood the feature request.
Request is for Array#index?
Updated by sawa (Tsuyoshi Sawada) over 10 years ago
=begin
- Matz: As for the method name, phluid61's explanation is exactly what I had in mind. And, some use cases are as shown below.
- phluid61: Your implementation looks perfect to me.
==== Use case 1
I want to delete and get from an array a
an element at position i
if there is such element. That element can be possibly nil
.
With index?
, it works like this:
a = ["a", nil, "b"]
deleted = :none
deleted = a.delete_at(3) if a.index?(3) # => Deletion did not happen.
deleted # => :none # I can be sure that deletion did not happen.
a = ["a", nil, "b"]
deleted = :none
deleted = a.delete_at(1) if a.index?(1) # => Deleted `nil`.
deleted # => nil # I can be sure that an element `nil` was deleted.
Without checking the index, I cannot tell whether deletion happened:
a = ["a", nil, "b"]
deleted = :none
deleted = a.delete_at(3) # => Deletion did not happen.
deleted # => nil # I cannot tell whether an element `nil` was deleted or deletion did not happen.
a = ["a", nil, "b"]
deleted = :none
deleted = a.delete_at(1) if a.index?(1) # => Deleted `nil`.
deleted # => nil # I cannot tell whether an element `nil` was deleted or deletion did not happen.
=== Use case 2
I want to prepend with :foo
an element at position i
if there is such element.
With index?
, it works like this:
a = ["a", "b"]
a.insert(1, :foo) if a.index?(1)
# => ["a", :foo, "b"]
a = ["a", "b"]
a.insert(3, :foo) if a.index?(3)
# => ["a", "b"]
Without index?
, unwanted nil
will be inserted
a = ["a", "b"]
a.insert(1, :foo)
# => ["a", :foo, "b"] # This is okay.
a = ["a", "b"]
a.insert(3, :foo)
# => ["a", "b", nil, :foo] # Unwanted result
=end
Updated by alexeymuranov (Alexey Muranov) over 10 years ago
Why not to use
3 < a.size
instead of
a.index?(3)
etc.?