to_na instance method

[dicom]

After subclassing NArray, I have discovered that NArray is missing a similar feature compared to Ruby's Array where you easily convert back to an Array.

With Array I can do this:

a = Array.new(3)
=> [nil, nil, nil]
a.class
=> Array
a.to_a.class
=> Array

class M < Array
end
=> nil
m = M.new(3)
=> [nil, nil, nil]
m.class
=> M
m.to_a.class
=> Array

I propose we add a to_na instance method to NArray, similar as the to_a instance method for Array. The documentation for Ruby's to_a method says:

Returns self. If called on a subclass of Array, converts the receiver to an Array object.

We can then do:

n = NArray.new(1,3)
=> NArray.byte(3):
[ 0, 0, 0 ]
n.class
=> NArray
n.to_na.class
=> NArray

class C < NArray
end
=> nil
c = C.new(1,3)
=> C.byte(3):
[ 0, 0, 0 ]
c.class
=> C
c.to_na.class
=> NArray

Is this possible?

[masa16]

1. I think the non-standard NArray class is in a different position from the build-in Array class.
2. If NArray provides Array#to_a and another library, e.g., NextArray, brings also Array#to_na, you cannot use NextArray and NArray simultaneously.

[dicom]

Perhaps you misunderstood me. I'm not proposing we touch Array class.

My proposal is we modify NArray class so that it behaves like Array when it is subclassed, by adding a to_na instance method to NArray.

I want to be able to do this with NArray:

n = NArray.new(1,3)
n.to_na.class
=> NArray

class C < NArray
end
c = C.new(1,3)
c.class
=> C
c.to_na.class
=> NArray

[masa16]

OK, now perhaps I understand. But it seems to me that to_na does not well express your intent. Instead, how about NArray.cast method?

class C < NArray; end

n = NArray[1..3]
=> NArray.int(3): 
[ 1, 2, 3 ]
C.cast(n)
=> C.int(3): 
[ 1, 2, 3 ]
C.cast(n,NArray::DFLOAT)
=> C.float(3): 
[ 1.0, 2.0, 3.0 ]

c = C.new(1,3,2)
=> C.byte(3,2): 
[ [ 0, 0, 0 ], 
  [ 0, 0, 0 ] ]
NArray.cast(c)
=> NArray.byte(3,2): 
[ [ 0, 0, 0 ], 
  [ 0, 0, 0 ] ]
NArray.cast(c,Float)
=> NArray.float(3,2): 
[ [ 0.0, 0.0, 0.0 ], 
  [ 0.0, 0.0, 0.0 ] ]

a = [[1,2],[3,4]]
=> [[1, 2], [3, 4]]
NArray.cast(a)
=> NArray.int(2,2): 
[ [ 1, 2 ], 
  [ 3, 4 ] ]
NArray.cast(a,NArray::DFLOAT)
=> NArray.float(2,2): 
[ [ 1.0, 2.0 ], 
  [ 3.0, 4.0 ] ]

Diff patch: https://github.com/masa16/narray/commit/b64f096039728b2c93d66f7f15e72cf8ca5691b7