# TypeResolver
[](https://hex.pm/packages/type_resolver)
TypeResolver is a library to resolve spec-types at compile time.
That is, reducing the specs to only native types by resolving user-defined,
built-in and remote types. The result is a type expressed in easy to
handle structs representing types.
## Rationale
Often we want to analyze spec-types in macros and derive functionality
from these types. Analyzing and working with AST from `Code.Typespec` or
Erlang AST is challenging and cumbersome. Furthermore, there is no
standalone library that resolves user-defined types, built-in types and
remote-types. This library fills this gap.
## Usage
The library offers the macro `TypeResolver.resolve/1`, that can be used
as follows:
```elixir
TypeResolver.resolve(integer() | String.t())
```
It returns the following representation:
```elixir
%TypeResolver.UnionT{
inner: [%TypeResolver.Types.IntegerT{}, %NamedType{inner: %TypeResolver.Types.BinaryT{} name: :t, module: String}]
}
```
The library is also capable of resolving type parameters.
For a complete list of result-types, see `TypeResolver.Types`.
## Type exporter
To resolve remote types, we rely on `Code.Typespec.fetch_types/1`. For
this function to work, the module has to be compiled into a beam file,
which cannot always be ensured at macro expansion time.
To handle this problem, we provide the module `TypeResolver.TypeExporter`.
This module takes care of types being exported and makes them available
at macro expansion time. The module has to be used in the remote module
that contains the type, as follows:
```elixir
defmodule MyRemoteModule do
use TypeResolver.TypeExporter
@type my_remote_t :: ...
end
```
*Note, that this is not a problem for library code since for dependencies,
all files have been compiled and written to beam-files before the compilation
of our own code.*
## Limitations
- Currently, this library cannot handle recursive types and does not detect
them. When using recursive times, compilation will be stuck in an infinite
recursion.
- Struct types don't get their member resolved
- Doesn't work with opaque types
## License
Copyright © 2024 Bravobike GmbH and Contributors
This project is licensed under the Apache 2.0 license.
