Return value polymorphic function

[zoziha]

For example, x = zeros(dim1, dim2, ...) function.

flag

We add a flag to the function, this flag is consistent with the precision of the return value.

x = zeros(dim1, dim2, ..., flag)

ref from: https://fortran-lang.discourse.group/t/fortran-function-return-value-polymorphism/1350/5

But we found that this method is actually not good for the user experience. We want to find other ways.

function name

We can abandon the idea of a polymorphic function interface and set up the following functions:

szeros / dzeros / qzeros
default: zeros = szeros

real(integer, kind)

Maybe we can imitate the standard function of Fortran, the real function.
ref from:

1. {"real", {{"a", AnyNumeric, Rank::elementalOrBOZ}, DefaultingKIND}
2. https://github.com/llvm/llvm-project/blob/d8805574c183484f055552855fa82d2e8932415e/flang/runtime/numeric.h#L22
3. https://github.com/llvm/llvm-project/blob/d8805574c183484f055552855fa82d2e8932415e/flang/runtime/numeric.cpp
4. https://github.com/llvm/llvm-project/blob/d480f968ad8b56d3ee4a6b6df5532d485b0ad01e/flang/runtime/type-code.cpp

real(integer, kind)

Final question

Should we implement the second method first. It will be more difficult to implement the third method? May need to use c/c++, so we need to ensure that fpm can build such code.
fortran-lang/fpm#353
https://github.com/fortran-lang/fpm/tree/master/example_packages/with_c

Or do we have a better way?