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Elixir macro utilities to make type-based programming easier
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lib/croma/struct_call_syntax.ex
defmodule Croma.StructCallSyntax do
@moduledoc """
This module provides a new syntax with `~>` operator for calls to functions that take structs as 1st arguments.
To enable the syntax `import` this module:
import Croma.StructCallSyntax
This module is not `import`ed by `use Croma`.
It is necessary to explicitly `import` this module.
## Examples
iex> defmodule S do
...> defstruct [:a, :b]
...> def f(s, i) do
...> s.a + s.b + i
...> end
...> end
...> import Croma.StructCallSyntax
...> s = %S{a: 1, b: 2}
...> s~>f(3) # => S.f(s, 3)
6
Note that calling functions with the `~>` syntax involves the following tradeoff:
- pros
- Shorter code
- Flexibility due to dynamic dispatch
- cons
- Run-time overhead due to dynamic dispatch
- Less information available to static analysis tools such as dialyzer
- Confusions due to new syntax
It is recommended that you think carefully about the above pros/cons for using this module.
If all you want is dynamic dispatching based on the receiver's type you can use protocol instead.
"""
@doc """
A macro that provides a syntax that resembles method invocations in typical OOP languages.
The module that defines the target function is extracted from the "receiver" struct (i.e. left hand side of `~>`) at run-time.
The "receiver" is then passed as the 1st argument to the function.
"""
defmacro struct ~> {f, _, atom} when is_atom(atom) do # without parameter list
quote bind_quoted: [struct: struct, f: f] do
%{__struct__: mod} = struct
apply(mod, f, [struct])
end
end
defmacro struct ~> {f, _, args} do # with parameter list
quote bind_quoted: [struct: struct, f: f, args: args] do
%{__struct__: mod} = struct
apply(mod, f, [struct | args])
end
end
end