View Source Module behaviour (Elixir v1.14.1)
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.
Module attributes
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.
@after_verify
(since v1.14.0)
A hook that will be invoked right after the current module is verified for
undefined functions, deprecations, etc. 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.
For detailed documentation, see the behaviour typespec documentation.
@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
in these cases:
if you mark a function with
@impl
when that function is not a callback.if you don't mark a function with
@impl
when other functions are marked with@impl
. If you mark one function with@impl
, you must mark all other callbacks for that behaviour as@impl
.
@impl
works on a per-context basis. If you generate a function through a macro
and mark it with @impl
, that won't affect the module where that function is
generated in.
@impl
also helps with maintainability by making it clear to other developers
that the function is implementing 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
# Will warn if neither Bar nor Baz specify a callback named bar/0.
@impl true
def bar(), do: :ok
# Will warn if Baz does not specify a callback named baz/0.
@impl Baz
def baz(), do: :ok
end
The code is now more readable, 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
(since v1.6.0)
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.
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 (without 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 one of these:
- a string (often a heredoc)
false
, which will make the entity invisible to documentation-extraction tools likeExDoc
- a keyword list, since Elixir 1.7.0
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, since Elixir 1.7.0 @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 the :since
key, which 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
.
Once this module is compiled, this information becomes available via
the Code.fetch_docs/1
function.
@dialyzer
Defines warnings to request or suppress when using :dialyzer
.
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 may use this information to ensure the module is recompiled
in case any of the external resources change, see for example:
mix compile.elixir
.
If the external resource does not exist, the module still has a dependency on it, causing the module to be recompiled as soon as the file is added.
@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.
Once this module is compiled, this information becomes available via
the Code.fetch_docs/1
function.
@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:
- the module environment
- the kind of the function/macro:
:def
,:defp
,:defmacro
, or:defmacrop
- the function/macro name
- the list of quoted arguments
- the list of quoted guards
- the quoted function body
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
.
Example
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
@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.
The function must have an arity of 0 (no arguments). If the function does
not return :ok
, 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
@vsn
Specify the module version. Accepts any valid Elixir value, for example:
defmodule MyModule do
@vsn "1.0"
end
Struct attributes
@derive
- derives an implementation for the given protocol for the struct defined in the current module@enforce_keys
- ensures the given keys are always set when building the struct defined in the current module
See defstruct/1
for more information on building and using structs.
Typespec attributes
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
For detailed documentation, see the typespec documentation.
Custom attributes
In addition to the built-in attributes outlined above, custom attributes may
also be added. Custom attributes are expressed using the @/1
operator followed
by a valid variable name. The value given to the custom attribute must be 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
.
Compile callbacks
There are three compilation callbacks, invoked in this order:
@before_compile
, @after_compile
, and @after_verify
.
They are described next.
@before_compile
A hook that will be invoked before the module is compiled. This is often used to change how the current module is being 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 will run in the order they are registered. 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 all callbacks run.
Note: the callback function/macro must be placed in a separate module (because when the callback is invoked, the current module does not yet exist).
Example
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"
@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 will run in the order they are registered.
Module
functions expecting not yet compiled modules (such as definitions_in/1
)
are still available at the time @after_compile
is invoked.
Example
defmodule MyModule do
@after_compile __MODULE__
def __after_compile__(env, _bytecode) do
IO.inspect(env)
end
end
@after_verify
A hook that will be invoked right after the current module is verified for undefined functions, deprecations, etc. A module is always verified after it is compiled. In Mix projects, a module is also verified when any of its runtime dependencies change. Therefore this is useful to perform verification of the current module while avoiding compile-time dependencies.
Accepts a module or a {module, function_name}
tuple. The function
must take one argument: the module name. When just a module is provided,
the function is assumed to be __after_verify__/2
.
Callbacks will run in the order they are registered.
Module
functions expecting not yet compiled modules are no longer available
at the time @after_verify
is invoked.
Example
defmodule MyModule do
@after_verify __MODULE__
def __after_verify__(module) do
IO.inspect(module)
:ok
end
end
Compile options
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 inCode.get_compiler_option/1
@compile {:debug_info, false}
- disables:debug_info
regardless of the corresponding setting inCode.get_compiler_option/1
. Note disabling:debug_info
is not recommended as it removes the ability of the Elixir compiler and other tools to static analyse the code. If you want to remove the:debug_info
while deploying, tools likemix release
already do such by default.@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@compile {:no_warn_undefined, Mod}
or@compile {:no_warn_undefined, {Mod, fun, arity}}
- does not warn if the given module or the givenMod.fun/arity
are not defined
Link to this section Summary
Callbacks
Provides runtime information about functions, macros, and other information defined by the module.
Functions
Returns all module attributes names defined in 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 and macros defined in module
.
Returns all functions defined in module
, according
to its kind.
Deletes the entry (or entries) for the given module attribute.
Deletes a definition from a module.
Evaluates the quoted contents in the given module's context.
Gets the given attribute from a module.
Returns the definition for the given name-arity pair.
Checks if the given attribute has been defined.
Makes the given functions in module
overridable.
Checks if a module is open.
Returns true
if tuple
in module
was marked as overridable
at some point.
Returns all overridable definitions in module
.
Puts a module attribute with key
and value
in the given module
.
Registers an attribute.
Returns information about module attributes used by Elixir.
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.
Copies the given spec as a callback.
Splits the given module name into binary parts.
Link to this section Types
@type def_kind() :: :def | :defp | :defmacro | :defmacrop
Link to this section Callbacks
@callback __info__(:attributes) :: keyword()
@callback __info__(:compile) :: [term()]
@callback __info__(:functions) :: keyword()
@callback __info__(:macros) :: keyword()
@callback __info__(:md5) :: binary()
@callback __info__(:module) :: module()
@callback __info__(:struct) :: [%{field: atom(), required: boolean()}] | nil
Provides runtime information about functions, macros, and other information defined by the module.
Each module gets an __info__/1
function when it's compiled. The function
takes one of the following items:
:attributes
- a keyword list with all persisted attributes:compile
- a list with compiler metadata:functions
- a keyword list of public functions and their arities:macros
- a keyword list of public macros and their arities:md5
- the MD5 of the module:module
- the module atom name:struct
- if the module defines a struct and if so each field in order
Link to this section Functions
Returns all module attributes names defined in module
.
This function can only be used on modules that have not yet been compiled.
Examples
defmodule Example do
@foo 1
Module.register_attribute(__MODULE__, :bar, accumulate: true)
:foo in Module.attributes_in(__MODULE__)
#=> true
:bar in Module.attributes_in(__MODULE__)
#=> true
end
Concatenates a list of aliases and returns a new alias.
It handles binaries and atoms.
Examples
iex> Module.concat([Foo, Bar])
Foo.Bar
iex> Module.concat([Foo, "Bar"])
Foo.Bar
Concatenates two aliases and returns a new alias.
It handles binaries and atoms.
Examples
iex> Module.concat(Foo, Bar)
Foo.Bar
iex> Module.concat(Foo, "Bar")
Foo.Bar
@spec 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
bytecode 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.
Examples
contents =
quote do
def world, do: true
end
Module.create(Hello, contents, Macro.Env.location(__ENV__))
Hello.world()
#=> true
Differences from defmodule
Module.create/3
works similarly to Kernel.defmodule/2
and return the same results. While one could also use
Kernel.defmodule/2
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.
@spec 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
and Kernel.macro_exported?/3
to check for
public functions and macros respectively in compiled modules.
Note that defines?
returns false for functions and macros that have
been defined but then marked as overridable and no other implementation
has been provided. You can check the overridable status by calling
overridable?/2
.
Examples
defmodule Example do
Module.defines?(__MODULE__, {:version, 0}) #=> false
def version, do: 1
Module.defines?(__MODULE__, {:version, 0}) #=> true
end
@spec 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
and Kernel.macro_exported?/3
to check for
public functions and macros respectively in compiled modules.
Examples
defmodule Example do
Module.defines?(__MODULE__, {:version, 0}, :def) #=> false
def version, do: 1
Module.defines?(__MODULE__, {:version, 0}, :def) #=> true
end
@spec 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.
@spec definitions_in(module()) :: [definition()]
Returns all functions and macros defined in module
.
It returns a list with all defined functions and macros, public and private,
in the shape of [{name, arity}, ...]
.
This function can only be used on modules that have not yet been compiled.
Use the Module.__info__/1
callback to get the public functions and macros in
compiled modules.
Examples
defmodule Example do
def version, do: 1
defmacrop test(arg), do: arg
Module.definitions_in(__MODULE__) #=> [{:version, 0}, {:test, 1}]
end
@spec definitions_in(module(), def_kind()) :: [definition()]
Returns all functions defined in module
, according
to its kind.
This function can only be used on modules that have not yet been compiled.
Use the Module.__info__/1
callback to get the public functions and macros in
compiled modules.
Examples
defmodule Example do
def version, do: 1
Module.definitions_in(__MODULE__, :def) #=> [{:version, 0}]
Module.definitions_in(__MODULE__, :defp) #=> []
end
Deletes the entry (or entries) for the given module attribute.
It returns the deleted attribute value. If the attribute has not
been set nor configured to accumulate, it returns nil
.
If the attribute is set to accumulate, then this function always returns a list. Deleting the attribute removes existing entries but the attribute will still accumulate.
Examples
defmodule MyModule do
Module.put_attribute(__MODULE__, :custom_threshold_for_lib, 10)
Module.delete_attribute(__MODULE__, :custom_threshold_for_lib)
end
@spec delete_definition(module(), definition()) :: boolean()
Deletes a definition from a module.
It returns true if the definition exists and it was removed, otherwise it returns false.
@spec 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.
Examples
defmodule Foo do
contents =
quote do
def sum(a, b), do: a + b
end
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
end
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.
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)
This function can only be used on modules that have not yet been compiled.
Use the Module.__info__/1
callback to get all persisted attributes, or
Code.fetch_docs/1
to retrieve all documentation related attributes in
compiled modules.
Examples
defmodule Foo do
Module.put_attribute(__MODULE__, :value, 1)
Module.get_attribute(__MODULE__, :value) #=> 1
Module.get_attribute(__MODULE__, :value, :default) #=> 1
Module.get_attribute(__MODULE__, :not_found, :default) #=> :default
Module.register_attribute(__MODULE__, :value, accumulate: true)
Module.put_attribute(__MODULE__, :value, 1)
Module.get_attribute(__MODULE__, :value) #=> [1]
end
@spec get_definition(module(), definition(), keyword()) :: {:v1, def_kind(), meta :: keyword(), [ {meta :: keyword(), arguments :: [Macro.t()], guards :: [Macro.t()], Macro.t()} ]} | nil
Returns the definition for the given name-arity pair.
It returns a tuple with the version
, the kind
,
the definition metadata
, and a list with each clause.
Each clause is a four-element tuple with metadata,
the arguments, the guards, and the clause AST.
The clauses are returned in the Elixir AST but a subset that has already been expanded and normalized. This makes it useful for analyzing code but it cannot be reinjected into the module as it will have lost some of its original context. Given this AST representation is mostly internal, it is versioned and it may change at any time. Therefore, use this API with caution.
Options
:skip_clauses
(since v1.14.0) - returns[]
instead of returning the clauses. This is useful when there is only an interest in fetching the kind and the metadata
Checks if the given attribute has been defined.
An attribute is defined if it has been registered with register_attribute/3
or assigned a value. If an attribute has been deleted with delete_attribute/2
it is no longer considered defined.
This function can only be used on modules that have not yet been compiled.
Examples
defmodule MyModule do
@value 1
Module.register_attribute(__MODULE__, :other_value)
Module.put_attribute(__MODULE__, :another_value, 1)
Module.has_attribute?(__MODULE__, :value) #=> true
Module.has_attribute?(__MODULE__, :other_value) #=> true
Module.has_attribute?(__MODULE__, :another_value) #=> true
Module.has_attribute?(__MODULE__, :undefined) #=> false
Module.delete_attribute(__MODULE__, :value)
Module.has_attribute?(__MODULE__, :value) #=> false
end
@spec make_overridable(module(), [definition()]) :: :ok
@spec make_overridable(module(), module()) :: :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.
Once a function or a macro is marked as overridable, it will
no longer be listed under definitions_in/1
or return true
when given to defines?/2
until another implementation is
given.
Checks if a module is open.
A module is "open" if it is currently being defined and its attributes and functions can be modified.
@spec overridable?(module(), definition()) :: boolean()
Returns true
if tuple
in module
was marked as overridable
at some point.
Note overridable?/2
returns true even if the definition was
already overridden. You can use defines?/2
to see if a definition
exists or one is pending.
Returns all overridable definitions in module
.
Note a definition is included even if it was was already overridden.
You can use defines?/2
to see if a definition exists or one is pending.
This function can only be used on modules that have not yet been compiled.
Examples
defmodule Example do
def foo, do: 1
def bar, do: 2
defoverridable foo: 0, bar: 0
def foo, do: 3
[bar: 0, foo: 0] = Module.overridables_in(__MODULE__) |> Enum.sort()
end
Puts a module attribute with key
and value
in the given module
.
Examples
defmodule MyModule do
Module.put_attribute(__MODULE__, :custom_threshold_for_lib, 10)
end
Registers an attribute.
By registering an attribute, a developer is able to customize how Elixir will store and accumulate the attribute values.
Options
When registering an attribute, two options can be given:
:accumulate
- several calls to the same attribute will accumulate instead of overriding 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
. Once an attribute has been
set to accumulate or persist, the behaviour cannot be reverted.
Examples
defmodule MyModule do
Module.register_attribute(__MODULE__, :custom_threshold_for_lib, accumulate: true)
@custom_threshold_for_lib 10
@custom_threshold_for_lib 20
@custom_threshold_for_lib #=> [20, 10]
end
Returns information about module attributes used by Elixir.
See the "Module attributes" section in the module documentation for more information on each attribute.
Examples
iex> map = Module.reserved_attributes()
iex> Map.has_key?(map, :moduledoc)
true
iex> Map.has_key?(map, :doc)
true
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 binaries and atoms.
Examples
iex> Module.safe_concat([List, Chars])
List.Chars
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 binaries and atoms.
Examples
iex> Module.safe_concat(List, Chars)
List.Chars
@spec spec_to_callback(module(), definition()) :: boolean()
Copies the given spec as a callback.
Returns true
if there is such a spec and it was copied as a callback.
If the function associated to the spec has documentation defined prior to
invoking this function, the docs are copied too.
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).
Examples
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"]