Is there a way to do mixin or similar during runtime?

I'm trying to read a csv file and extract data types. Any ideas on how this should be approached in D are greatly appreciated.

On Friday, 27 August 2021 at 06:52:10 UTC, Kirill wrote:

remember D is a statically compiled language, mixin is for generating code, so, it won't work except you have a runtime code parser.

you may need a scripting language embedded in your D app to achieve this.

thx.

On Friday, 27 August 2021 at 06:52:10 UTC, Kirill wrote:

You cannot mixin at runtime. However, it is fairly easy to map a finite and CT-know set of argument to runtime arguments via static foreach.
Could you give us example of the content of your CSV file and what you are trying to do ?

On Friday, 27 August 2021 at 09:51:46 UTC, Mathias LANG wrote:

Each csv file will be different.

For example:

name;surname;age;grade
Alex;Wong;18;87
John;Doe;19;65
Alice;Doe;18;73
etc...

I'd like to extract the data types automatically. For instance, if using tuples:

Tuple!(string, string, int, int) ...

instead I'd like to have:

auto mytuple = read_csv(path); // returns Tuple!(string, string, int, int)[]

On Friday, 27 August 2021 at 10:34:27 UTC, Kirill wrote:

name;surname;age;grade
Alex;Wong;18;87
John;Doe;19;65
Alice;Doe;18;73
etc...

Tuple!(string, string, int, int) ...

auto mytuple = read_csv(path); // returns Tuple!(string, string, int, int)[]

mytuple needs to have a type that's known at compile-time, so this isn't possible. In the types are only dynamically known, then you have to deal in dynamic types. One way could be to have a read_csv that returns an array of https://dlang.org/phobos/std_variant.html

On 8/27/21 6:34 AM, Kirill wrote:

name;surname;age;grade
Alex;Wong;18;87
John;Doe;19;65
Alice;Doe;18;73
etc...

Tuple!(string, string, int, int) ...

auto mytuple = read_csv(path); // returns Tuple!(string, string, int, int)[]

So you can't build "new types" at runtime that are usable after your code is compiled. But there are options:

1. You can parse the CSV at compile-time using import("types.csv"); and then processing the resulting string using CTFE (not sure if std.csv does this, but I'd expect it to). Then you can use the resulting thing to generate string mixins that can generate types. This has the drawback that you need to recompile when your csv input changes.

2. You can create a dynamic type that deals with the CSV data. It looks from your CSV data you are inferring the "type" from the data itself, which is complex in itself. In this case, you'd use it kind of like a JSON object, where you index the fields by name instead of using obj.name, and you'd have to extract the type dynamically from the type inference you'd have to write. This is pretty much what std.csv does, though you can dress it up a bit more.

Without the CSV telling you types, it's hard to make something "easy". I have written code that extracts from JSON data and database data serializable struct types, and builds a D file, but it's never clean-cut, and sometimes you have to hand-edit that stuff. This is about as "easy" as it gets, just have the computer do most of the heavy lifting, and then massage it into something usable.

-Steve

On Friday, 27 August 2021 at 06:52:10 UTC, Kirill wrote:

mixin at runtime not possible.
Source code compilation and runing in runtime not possible. But!

But you can impement this!

Steps:

1. Need D compiller
2. In runtime you can compile mixin to dynamic library (.so or .dll) using external command: dmd ...
3. Load dynamic library using dlopen() dlsym() dlclose(). (on Windows: LoadLibrary(), GetProcAdres(), FreLibrary())
4. Call mixin functions, variables
5. Done!

Packages bindbc-, derelict- uses dynamic loading. You can use both as examples.