Interfacer: Create Interfaces using THICC Pointers in C++

Tired of virtual and its gross hidden __vtable pointer? Do you want something more akin to Rust's as &dyn <trait>? Need more control of your vtables? Are you tired of using filthy inheritance to achieve your goals? This is probably for you. Interfacer is a simple code generation tool that creates "fat pointer" interfaces from python dicts. It also generates a helper as_interfacename function to make it easy to integrate it to your code, but you still can specify your own vtables just fine.

Installation

There's no installation. Copy the interfacer.py file to your project and use it as you wish.

Usage

NOTE: Requires C++14 or later, ideally you should use C++17 or later as it can take advantage of better constexpr

Simple concrete type (Allocator)

Also look at the gen.py file.

from interfacer import interface

# Helper function that creates an Interface object
interface('Allocator', {
    # Use the @include directive to add files
    '@include': ['<cstddef>', 'types.hpp'],
    # You can use @namespace to prepend namespaces to the interface
    # Use [''] for an anonymous namespace
    'namespace': ['mem', 'virt'],
    # All declarations follow ID:TYPE form, spaces are ignored
    'alloc: void*': ['nbytes: usize'],
    'alloc_undef: void*': ['nbytes: usize'],
    'realloc: void*': ['p: void*', 'nbytes: usize'],
    'free: void': ['p: void*'],
    # Empty list means no args
    'free_all: void': [],
    # To mark a procedure as const, just drop a @const in its argument list
    'has_address: bool': ['p: void*', '@const']
}).generate_file('examples/allocator.hpp', guard='pragma')
# When generating to a file, you can choose the header guard style: ifdef, pragma or none(default)

Generic container type (List)

import interfacer as i
interface('List', {
    # Pass template args in the @template field
    '@template':['T: typename'],
    'at: T&':['idx: int'],
    'len: int':['@const']
}).generate_file('examples/list.hpp')

Limitations

Because this is mainly a hack you can expect a bunch of edge cases, as Interfacer does not parse C++ code, and never will as doing so is insanely complicated and you're better off just using a better language.

Interfaces are just plain function pointer tables, you cannot add procedure overloading to interfaces, as that would require Interfacer using its own name mangling rules that would create even more problems. You can however, choose a specific overload of a function to be in the vtable, you can just copy-paste the wrapper and do a specialization for your datatype where you change the desired vtable fields.

NOTE: Vtables must be static, as they will live through the whole program, you could make some heap-allocated (potentially mutable) vtable if you're insane tho.