$ iex -S mix
Erlang/OTP 24 [erts-12.0.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]
Interactive Elixir (1.13.0) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> B.__info__(:functions)
[bar: 0, foo: 0, hoge: 0, new_bar: 0, new_foo: 0, new_hoge: 0]
iex(2)> B.new_bar()
"geneareted from bar."
iex(3)> B.new_foo()
"geneareted from foo."
iex(4)> B.new_hoge()
"geneareted from hoge."
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January 31, 2022 13:49
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定義された関数を参照してmacroで新しい関数定義を追加する
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defmodule A do | |
defmacro __using__(_opts) do | |
quote do | |
Module.register_attribute(__MODULE__, :funs, accumulate: true) | |
@on_definition {A, :on_definition} | |
@before_compile {A, :before_compile} | |
end | |
end | |
def on_definition(env, kind, name, args, guards, body) do | |
Module.put_attribute(env.module, :funs, %{ | |
kind: kind, | |
name: name, | |
args: args, | |
guards: guards, | |
body: body | |
}) | |
end | |
defmacro before_compile(env) do | |
funs = Module.get_attribute(env.module, :funs, []) | |
Enum.map(funs, fn %{name: name} -> | |
quote do | |
def unquote(:"new_#{name}")() do | |
"geneareted from #{unquote(name)}." | |
end | |
end | |
end) | |
end | |
end |
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defmodule B do | |
use A | |
def foo(), do: "foo" | |
def bar(), do: "bar" | |
def hoge(), do: "hoge" | |
end |
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