Provides functions to deal with modules during compilation time.
It allows a developer to dynamically add, delete and register attributes, attach documentation and so forth.
After a module is compiled, using many of the functions in this module will raise errors, since it is out of their scope to inspect runtime data. Most of the runtime data can be inspected via the __info__/1
function attached to each compiled module.
Each module can be decorated with one or more attributes. The following ones are currently defined by Elixir:
@after_compile
A hook that will be invoked right after the current module is compiled. Accepts a module or a {module, function_name}
. See the “Compile callbacks” section below.
@before_compile
A hook that will be invoked before the module is compiled. Accepts a module or a {module, function_or_macro_name}
tuple. See the “Compile callbacks” section below.
@behaviour
Note the British spelling!
Behaviours can be referenced by modules to ensure they implement required specific function signatures defined by @callback
.
For example, you could specify a URI.Parser
behaviour as follows:
defmodule URI.Parser do @doc "Defines a default port" @callback default_port() :: integer @doc "Parses the given URL" @callback parse(uri_info :: URI.t) :: URI.t end
And then a module may use it as:
defmodule URI.HTTP do @behaviour URI.Parser def default_port(), do: 80 def parse(info), do: info end
If the behaviour changes or URI.HTTP
does not implement one of the callbacks, a warning will be raised.
@impl
To aid in the correct implementation of behaviours, you may optionally declare @impl
for implemented callbacks of a behaviour. This makes callbacks explicit and can help you to catch errors in your code. The compiler will warn you if you mark a function as @impl
when in fact it is not a callback, and vice-versa. It also helps with maintainability by making it clear to other developers that the function’s purpose is to implement a callback.
Using @impl
the example above can be rewritten as:
defmodule URI.HTTP do @behaviour URI.parser @impl true def default_port(), do: 80 @impl true def parse(info), do: info end
You may pass either false
, true
, or a specific behaviour to @impl
.
defmodule Foo do @behaviour Bar @behaviour Baz @impl true # will warn if neither Bar nor Baz specify a callback named bar/0 def bar(), do: :ok @impl Baz # will warn if Baz does not specify a callback named baz/0 def baz(), do: :ok end
Readability of the code is increased, as it is now clear which functions are part of your API and which ones are callback implementations. To reinforce this idea, @impl true
automatically marks the function as @doc false
, disabling documentation unless @doc
is explicitly set.
@compile
Defines options for module compilation. This is used to configure both Elixir and Erlang compilers, as any other compilation pass added by external tools. For example:
defmodule MyModule do @compile {:inline, my_fun: 1} def my_fun(arg) do to_string(arg) end end
Multiple uses of @compile
will accumulate instead of overriding previous ones. See the “Compile options” section below.
@deprecated
Provides the deprecation reason for a function. For example:
defmodule Keyword do @deprecated "Use Kernel.length/1 instead" def size(keyword) do length(keyword) end end
The Mix compiler automatically looks for calls to deprecated modules and emit warnings during compilation, computed via mix xref warnings
.
Using the @deprecated
attribute will also be reflected in the documentation of the given function and macro. You can choose between the @deprecated
attribute and the documentation metadata to provide hard-deprecations (with warnings) and soft-deprecations (with warnings):
This is a soft-deprecation as it simply annotates the documentation as deprecated:
@doc deprecated: "Use Kernel.length/1 instead" def size(keyword)
This is a hard-deprecation as it emits warnings and annotates the documentation as deprecated:
@deprecated "Use Kernel.length/1 instead" def size(keyword)
Currently @deprecated
only supports functions and macros. However you can use the :deprecated
key in the annotation metadata to annotate the docs of modules, types and callbacks too.
We recommend using this feature with care, especially library authors. Deprecating code always pushes the burden towards library users. We also recommend for deprecated functionality to be maintained for long periods of time, even after deprecation, giving developers plenty of time to update (except for cases where keeping the deprecated API is undesired, such as in the presence of security issues).
@doc
and @typedoc
Provides documentation for the entity that follows the attribute. @doc
is to be used with a function, macro, callback, or macrocallback, while @typedoc
with a type (public or opaque).
Accepts a string (often a heredoc) or false
where @doc false
will make the entity invisible to documentation extraction tools like ExDoc. For example:
defmodule MyModule do @typedoc "This type" @typedoc since: "1.1.0" @type t :: term @doc "Hello world" @doc since: "1.1.0" def hello do "world" end @doc """ Sums `a` to `b`. """ def sum(a, b) do a + b end end
As can be seen in the example above, @doc
and @typedoc
also accept a keyword list that serves as a way to provide arbitrary metadata about the entity. Tools like ExDoc and IEx may use this information to display annotations. A common use case is since
that may be used to annotate in which version the function was introduced.
As illustrated in the example, it is possible to use these attributes more than once before an entity. However, the compiler will warn if used twice with binaries as that replaces the documentation text from the preceding use. Multiple uses with keyword lists will merge the lists into one.
Note that since the compiler also defines some additional metadata, there are a few reserved keys that will be ignored and warned if used. Currently these are: :opaque
and :defaults
.
@dialyzer
Defines warnings to request or suppress when using a version of :dialyzer
that supports module attributes.
Accepts an atom, a tuple, or a list of atoms and tuples. For example:
defmodule MyModule do @dialyzer {:nowarn_function, my_fun: 1} def my_fun(arg) do M.not_a_function(arg) end end
For the list of supported warnings, see :dialyzer
module.
Multiple uses of @dialyzer
will accumulate instead of overriding previous ones.
@external_resource
Specifies an external resource for the current module.
Sometimes a module embeds information from an external file. This attribute allows the module to annotate which external resources have been used.
Tools like Mix may use this information to ensure the module is recompiled in case any of the external resources change.
@file
Changes the filename used in stacktraces for the function or macro that follows the attribute, such as:
defmodule MyModule do @doc "Hello world" @file "hello.ex" def hello do "world" end end
@moduledoc
Provides documentation for the current module.
defmodule MyModule do @moduledoc """ A very useful module. """ @moduledoc authors: ["Alice", "Bob"] end
Accepts a string (often a heredoc) or false
where @moduledoc false
will make the module invisible to documentation extraction tools like ExDoc.
Similarly to @doc
also accepts a keyword list to provide metadata about the module. For more details, see the documentation of @doc
above.
@on_definition
A hook that will be invoked when each function or macro in the current module is defined. Useful when annotating functions.
Accepts a module or a {module, function_name}
tuple. See the “Compile callbacks” section below.
@on_load
A hook that will be invoked whenever the module is loaded.
Accepts the function name (as an atom) of a function in the current module or {function_name, 0}
tuple where function_name
is the name of a function in the current module. The function must have arity 0 (no arguments) and has to return :ok
, otherwise the loading of the module will be aborted. For example:
defmodule MyModule do @on_load :load_check def load_check do if some_condition() do :ok else :abort end end def some_condition do false end end
Modules compiled with HiPE would not call this hook.
@vsn
Specify the module version. Accepts any valid Elixir value, for example:
defmodule MyModule do @vsn "1.0" end
The following attributes are part of typespecs and are also built-in in Elixir:
@type
- defines a type to be used in @spec
@typep
- defines a private type to be used in @spec
@opaque
- defines an opaque type to be used in @spec
@spec
- provides a specification for a function @callback
- provides a specification for a behaviour callback @macrocallback
- provides a specification for a macro behaviour callback @optional_callbacks
- specifies which behaviour callbacks and macro behaviour callbacks are optional @impl
- declares an implementation of a callback function or macro In addition to the built-in attributes outlined above, custom attributes may also be added. A custom attribute is any valid identifier prefixed with an @
and followed by a valid Elixir value:
defmodule MyModule do @custom_attr [some: "stuff"] end
For more advanced options available when defining custom attributes, see register_attribute/3
.
There are three callbacks that are invoked when functions are defined, as well as before and immediately after the module bytecode is generated.
@after_compile
A hook that will be invoked right after the current module is compiled.
Accepts a module or a {module, function_name}
tuple. The function must take two arguments: the module environment and its bytecode. When just a module is provided, the function is assumed to be __after_compile__/2
.
Callbacks registered first will run last.
defmodule MyModule do @after_compile __MODULE__ def __after_compile__(env, _bytecode) do IO.inspect env end end
@before_compile
A hook that will be invoked before the module is compiled.
Accepts a module or a {module, function_or_macro_name}
tuple. The function/macro must take one argument: the module environment. If it’s a macro, its returned value will be injected at the end of the module definition before the compilation starts.
When just a module is provided, the function/macro is assumed to be __before_compile__/1
.
Callbacks registered first will run last. Any overridable definition will be made concrete before the first callback runs. A definition may be made overridable again in another before compile callback and it will be made concrete one last time after after all callbacks run.
Note: unlike @after_compile
, the callback function/macro must be placed in a separate module (because when the callback is invoked, the current module does not yet exist).
defmodule A do defmacro __before_compile__(_env) do quote do def hello, do: "world" end end end defmodule B do @before_compile A end B.hello() #=> "world"
@on_definition
A hook that will be invoked when each function or macro in the current module is defined. Useful when annotating functions.
Accepts a module or a {module, function_name}
tuple. The function must take 6 arguments:
:def
, :defp
, :defmacro
, or :defmacrop
Note the hook receives the quoted arguments and it is invoked before the function is stored in the module. So Module.defines?/2
will return false
for the first clause of every function.
If the function/macro being defined has multiple clauses, the hook will be called for each clause.
Unlike other hooks, @on_definition
will only invoke functions and never macros. This is to avoid @on_definition
callbacks from redefining functions that have just been defined in favor of more explicit approaches.
When just a module is provided, the function is assumed to be __on_definition__/6
.
defmodule Hooks do def on_def(_env, kind, name, args, guards, body) do IO.puts "Defining #{kind} named #{name} with args:" IO.inspect args IO.puts "and guards" IO.inspect guards IO.puts "and body" IO.puts Macro.to_string(body) end end defmodule MyModule do @on_definition {Hooks, :on_def} def hello(arg) when is_binary(arg) or is_list(arg) do "Hello" <> to_string(arg) end def hello(_) do :ok end end
The @compile
attribute accepts different options that are used by both Elixir and Erlang compilers. Some of the common use cases are documented below:
@compile :debug_info
- includes :debug_info
regardless of the corresponding setting in Code.compiler_options/1
@compile {:debug_info, false}
- disables :debug_info
regardless of the corresponding setting in Code.compiler_options/1
@compile {:inline, some_fun: 2, other_fun: 3}
- inlines the given name/arity pairs. Inlining is applied locally, calls from another module are not affected by this option
@compile {:autoload, false}
- disables automatic loading of modules after compilation. Instead, the module will be loaded after it is dispatched to
You can see a handful more options used by the Erlang compiler in the documentation for the :compile
module.
Concatenates a list of aliases and returns a new alias
Concatenates two aliases and returns a new alias
Creates a module with the given name and defined by the given quoted expressions
Checks if the module defines the given function or macro
Checks if the module defines a function or macro of the given kind
Checks if the current module defines the given type (private, opaque or not)
Returns all functions defined in module
Returns all functions defined in module
, according to its kind
Deletes the module attribute that matches the given key
Evaluates the quoted contents in the given module’s context
Gets the given attribute from a module
Makes the given functions in module
overridable
Checks if a module is open
Returns true
if tuple
in module
is marked as overridable
Puts a module attribute with key
and value
in the given module
Registers an attribute
Concatenates a list of aliases and returns a new alias only if the alias was already referenced
Concatenates two aliases and returns a new alias only if the alias was already referenced
Converts the given spec to a callback
Splits the given module name into binary parts
concat([binary() | atom()]) :: atom()
Concatenates a list of aliases and returns a new alias.
iex> Module.concat([Foo, Bar]) Foo.Bar iex> Module.concat([Foo, "Bar"]) Foo.Bar
concat(binary() | atom(), binary() | atom()) :: atom()
Concatenates two aliases and returns a new alias.
iex> Module.concat(Foo, Bar) Foo.Bar iex> Module.concat(Foo, "Bar") Foo.Bar
create(module(), Macro.t(), Macro.Env.t() | keyword()) :: {:module, module(), binary(), term()}
Creates a module with the given name and defined by the given quoted expressions.
The line where the module is defined and its file must be passed as options.
It returns a tuple of shape {:module, module, binary, term}
where module
is the module name, binary
is the module byte code and term
is the result of the last expression in quoted
.
Similar to Kernel.defmodule/2
, the binary will only be written to disk as a .beam
file if Module.create/3
is invoked in a file that is currently being compiled.
contents = quote do def world, do: true end Module.create(Hello, contents, Macro.Env.location(__ENV__)) Hello.world #=> true
defmodule
Module.create/3
works similarly to Kernel.defmodule/2
and return the same results. While one could also use defmodule
to define modules dynamically, this function is preferred when the module body is given by a quoted expression.
Another important distinction is that Module.create/3
allows you to control the environment variables used when defining the module, while Kernel.defmodule/2
automatically uses the environment it is invoked at.
defines?(module(), definition()) :: boolean()
Checks if the module defines the given function or macro.
Use defines?/3
to assert for a specific type.
This function can only be used on modules that have not yet been compiled. Use Kernel.function_exported?/3
to check compiled modules.
defmodule Example do Module.defines? __MODULE__, {:version, 0} #=> false def version, do: 1 Module.defines? __MODULE__, {:version, 0} #=> true end
defines?(module(), definition(), def_kind()) :: boolean()
Checks if the module defines a function or macro of the given kind
.
kind
can be any of :def
, :defp
, :defmacro
, or :defmacrop
.
This function can only be used on modules that have not yet been compiled. Use Kernel.function_exported?/3
to check compiled modules.
defmodule Example do Module.defines? __MODULE__, {:version, 0}, :defp #=> false def version, do: 1 Module.defines? __MODULE__, {:version, 0}, :defp #=> false end
defines_type?(module(), definition()) :: boolean()
Checks if the current module defines the given type (private, opaque or not).
This function is only available for modules being compiled.
definitions_in(module()) :: [definition()]
Returns all functions defined in module
.
defmodule Example do def version, do: 1 Module.definitions_in __MODULE__ #=> [{:version, 0}] end
definitions_in(module(), def_kind()) :: [definition()]
Returns all functions defined in module
, according to its kind.
defmodule Example do def version, do: 1 Module.definitions_in __MODULE__, :def #=> [{:version, 0}] Module.definitions_in __MODULE__, :defp #=> [] end
delete_attribute(module(), atom()) :: term()
Deletes the module attribute that matches the given key.
It returns the deleted attribute value (or nil
if nothing was set).
defmodule MyModule do Module.put_attribute __MODULE__, :custom_threshold_for_lib, 10 Module.delete_attribute __MODULE__, :custom_threshold_for_lib end
eval_quoted( module() | Macro.Env.t(), Macro.t(), list(), keyword() | Macro.Env.t() ) :: term()
Evaluates the quoted contents in the given module’s context.
A list of environment options can also be given as argument. See Code.eval_string/3
for more information.
Raises an error if the module was already compiled.
defmodule Foo do contents = quote do: (def sum(a, b), do: a + b) Module.eval_quoted __MODULE__, contents end Foo.sum(1, 2) #=> 3
For convenience, you can pass any Macro.Env
struct, such as __ENV__/0
, as the first argument or as options. Both the module and all options will be automatically extracted from the environment:
defmodule Foo do contents = quote do: (def sum(a, b), do: a + b) Module.eval_quoted __ENV__, contents end Foo.sum(1, 2) #=> 3
Note that if you pass a Macro.Env
struct as first argument while also passing opts
, they will be merged with opts
having precedence.
get_attribute(module(), atom()) :: term()
Gets the given attribute from a module.
If the attribute was marked with accumulate
with Module.register_attribute/3
, a list is always returned. nil
is returned if the attribute has not been marked with accumulate
and has not been set to any value.
The @
macro compiles to a call to this function. For example, the following code:
@foo
Expands to something akin to:
Module.get_attribute(__MODULE__, :foo)
defmodule Foo do Module.put_attribute __MODULE__, :value, 1 Module.get_attribute __MODULE__, :value #=> 1 Module.register_attribute __MODULE__, :value, accumulate: true Module.put_attribute __MODULE__, :value, 1 Module.get_attribute __MODULE__, :value #=> [1] end
make_overridable(module(), module()) :: :ok
make_overridable(module(), [definition()]) :: :ok
Makes the given functions in module
overridable.
An overridable function is lazily defined, allowing a developer to customize it. See Kernel.defoverridable/1
for more information and documentation.
open?(module()) :: boolean()
Checks if a module is open.
A module is “open” if it is currently being defined and its attributes and functions can be modified.
overridable?(module(), definition()) :: boolean()
Returns true
if tuple
in module
is marked as overridable.
put_attribute(module(), atom(), term()) :: :ok
Puts a module attribute with key
and value
in the given module
.
defmodule MyModule do Module.put_attribute __MODULE__, :custom_threshold_for_lib, 10 end
register_attribute(module(), atom(), accumulate: boolean(), persist: boolean()) :: :ok
Registers an attribute.
By registering an attribute, a developer is able to customize how Elixir will store and accumulate the attribute values.
When registering an attribute, two options can be given:
:accumulate
- several calls to the same attribute will accumulate instead of override the previous one. New attributes are always added to the top of the accumulated list.
:persist
- the attribute will be persisted in the Erlang Abstract Format. Useful when interfacing with Erlang libraries.
By default, both options are false
.
defmodule MyModule do Module.register_attribute __MODULE__, :custom_threshold_for_lib, accumulate: true, persist: false @custom_threshold_for_lib 10 @custom_threshold_for_lib 20 @custom_threshold_for_lib #=> [20, 10] end
safe_concat([binary() | atom()]) :: atom()
Concatenates a list of aliases and returns a new alias only if the alias was already referenced.
If the alias was not referenced yet, fails with ArgumentError
. It handles charlists, binaries and atoms.
iex> Module.safe_concat([Module, Unknown]) ** (ArgumentError) argument error iex> Module.safe_concat([List, Chars]) List.Chars
safe_concat(binary() | atom(), binary() | atom()) :: atom()
Concatenates two aliases and returns a new alias only if the alias was already referenced.
If the alias was not referenced yet, fails with ArgumentError
. It handles charlists, binaries and atoms.
iex> Module.safe_concat(Module, Unknown) ** (ArgumentError) argument error iex> Module.safe_concat(List, Chars) List.Chars
spec_to_callback(module(), definition()) :: boolean()
Converts the given spec to a callback.
Returns true
if there is such a spec and it was converted to a callback.
split(module() | String.t()) :: [String.t(), ...]
Splits the given module name into binary parts.
module
has to be an Elixir module, as split/1
won’t work with Erlang-style modules (for example, split(:lists)
raises an error).
split/1
also supports splitting the string representation of Elixir modules (that is, the result of calling Atom.to_string/1
with the module name).
iex> Module.split(Very.Long.Module.Name.And.Even.Longer) ["Very", "Long", "Module", "Name", "And", "Even", "Longer"] iex> Module.split("Elixir.String.Chars") ["String", "Chars"]
© 2012 Plataformatec
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/elixir/1.7.3/Module.html