Enhance `string_type` constructor

[zoziha]

Motivation

As I said in #562 , we can enhance the constructor of string_type to support conversion of other types (integer, real, logical, complex) to string_type, and support format argument.

The important thing is that this constructor can be elemental, type(string_type) is very good at constructing flexible string arrays, but to_string can only be pure because character(:), allcoatable.

At this stage, string_type only constructs strings from character, integer, and logical types.

Prior Art

• interface string_type (elemental)
• interface to_string (pure)

Additional Information

No response

[milancurcic]

I like the idea. I see that stdlib_strings depends on stdlib_string_type module. In practice, would you duplicate some code from to_string to implement a specific constructor for string_type?

[awvwgk]

Do we have an implementation for creating strings from real and complex numbers without using internal IO in Fortran?

[St-Maxwell]

I have just implemented a Fortran version of Ryu which can effectively convert floating point numbers to decimal strings. After the codes being fully tested, I think they can be adopted by stdlib.

Currently it just generates the shortest representation of a floating number and doesn't support formatting. The original C implementation has Ryu printf which supports precision parameter. And I am trying to translate the C codes into Fortran.

[jvdp1]

@St-Maxwell: is this related to the stdlib to_string that support various types?
It seems that your implementation does not rely on internal IO (as in stdlib). Therefore, it would be interesting to compare the different performances.

[St-Maxwell]

@jvdp1 I plan to implement conversion routines for real32 and real64. Case of real128 will fall back to internal IO until we implement Ryu for this kind later.

[Divyansh200102]

@zoziha is this issue still open and also can you please give an idea of how can i resolve this issue?