Emulate C++'s typedefs with structs

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
csharp
Domain
api

Research direction

Start by tracing the H5F.create and H5F.get_filesize declarations and their current Int32 return types. Review how version-dependent hid_t values are represented across the P/Invoke API, then determine the affected callers and tests. Done means distinct marshable wrapper types preserve the return semantics and hid_t width while improving IntelliSense.

Written by the indexing model from the issue text.

Description

At the current state e.g. the functions H5F.create( .. ) and H5F.get_filesize( .. ) both return Int32 even though create returns an actual id and get_filesize only indicates if there was an error. So the real meanings are lost in C# when using IntelliSense.

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I suggest to wrap the values into structs to create marshable wrapper types to preserve the semantics that are carried by aliases (C++ typedefs).

So instead of adding a lot usings on top of every file:

using herr_t = System.Int32;
#if HDF5_VER1_10
using hid_t = System.Int64;
#else
using hid_t = System.Int32;
#endif

I would add these types ONCE into the library:

public struct herr_t
{
    public System.Int32 Value;
    public static implicit operator System.Int32(herr_t value) => value.Value;
}

public struct hid_t
{
#if HDF5_VER1_10
    public System.Int64 Value;
    public static implicit operator System.Int64( hid_t value ) => value.Value;
#else
    public System.Int32 Value;
    public static implicit operator System.Int32(hid_t value) => value.Value;
#endif
}

This allows would lead to much more readable IntelliSense hints and enables the use of ad-hoc polymorphism like:

public static class HdfPInvokeHelpers
{
    public static void ThrowOnError(this herr_t value)
    {
        if (value < 0)
            throw new Exception(H5EHelper.GetErrorStack().ToString());
    }

    public static hid_t ThrowOnError(this hid_t value)
    {
        if (value < 0)
            throw new Exception(H5EHelper.GetErrorStack().ToString());
        return value;
    }
}

class Program
{
    static void Main(string[] args)
    {
        var file = H5F.create("file.h5", H5F.ACC_RDONLY, H5P.DEFAULT, H5P.DEFAULT).ThrowOnError();
        ulong size;
        H5F.get_filesize(file, ref size).ThrowOnError();
    }
}
Update

Missing cross-define for hid_t added.

Dominant language
C#
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Forks
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