Creating arrays similar to other arrays

[Giels]

The current rust interface to arrayfire uses stricter type enforcement than the underlying C interface, which is good for safety but also prevents using e.g. arrayfire::constant to create an array of the same type as another array, because

1- ConstGenerator is private
2- get_type can't return a type (so it returns a DType)
3- There is no way to use a DType instead of a type on which HasAfEnum is defined when such a thing is required (i.e. pretty much everywhere)
4- HasAfEnum's get_af_dtype does not use a ...self parameter so it's not possible to define HasAfEnum on a DType wrapper.

I see two obvious possible solutions for this issue:

1- Implement HasAfEnum for DType and possibly make get_af_dtype take a ...self argument as a result
2- Expose helper functions zeros_like and ones_like (at least) which yield, respectively, an array of zeros with the same type and shape as the input (an array), or likewise for an array of ones. With these, it's possible to create arbitrary arrays with the same dimensions and type as another array.

However I don't know if limiting the solution to this would impact performance too much. I recall reading that arrayfire can optimize sequences of operations but I don't know if such a usecase is covered.

[9prady9]

@Giels Alternative (2) makes sense, however (1) doesn't to me. Can you please elaborate on how implementing HasAfEnum for DType is going to help this use case.

[9prady9]

@Giels I have created a function constant_like that does what you requested. Please follow #94 to track it's progress into the crate.

[Giels]

My idea for alternative (1) was ill-thought, and as you say it doesn't make sense, ultimately.
The constant_like is a good solution. Thanks.