defmodule Estructura do
@moduledoc ~S"""
`Estructura` is a set of extensions for Elixir structures,
such as `Access` implementation, `Enumerable` and `Collectable`
implementations, validations and test data generation via `StreamData`.
`Estructura` simplifies the following
* `Access` implementation for structs
* `Enumerable` implementation for structs (as maps)
* `Collectable` implementation for one of struct’s fields (as `MapSet` does)
* `StreamData` generation of structs for property-based testing
### Use Options
`use Estructura` accepts four keyword arguments.
* `access: true | false | :lazy` whether to generate the `Access` implementation, default `true`;
when `true` or `:lazy`, it also produces `put/3` and `get/3` methods to be used with `coercion`
and `validation`, when `:lazy`, instances of `Estructura.Lazy` are understood as values
* `coercion: boolean() | [key()]` whether to generate the bunch of `coerce_×××/1` functions
to be overwritten by implementations, default `false`
* `validation: boolean() | [key()]` whether to generate the bunch of `validate_×××/1` functions
to be overwritten by implementations, default `false`
* `enumerable: boolean()` whether to generate the `Enumerable` porotocol implementation, default `false`
* `collectable: false | key()` whether to generate the `Collectable` protocol implementation,
default `false`; if non-falsey atom is given, it must point to a struct field where `Collectable`
would collect. Should be one of `list()`, `map()`, `MapSet.t()`, `bitstribg()`
* `generator: %{optional(key()) => Estructura.Config.generator()}` the instructions
for the `__generate__/{0,1}` functions that would produce the target structure values suitable
for usage in `StreamData` property testing; the generated `__generator__/1` function is overwritable.
Please note, that setting `coercion` and/or `validation` to truthy values has effect
if and only if `access` has been also set to `true`.
Typical example of usage would be:
```elixir
defmodule MyStruct do
use Estructura,
access: true,
coercion: [:foo], # requires `c:MyStruct.Coercible.coerce_foo/1` impl
validation: true, # requires `c:MyStruct.Validatable.validate_×××/1` impls
enumerable: true,
collectable: :bar,
generator: [
foo: {StreamData, :integer},
bar: {StreamData, :list_of, [{StreamData, :string, [:alphanumeric]}]},
baz: {StreamData, :fixed_map,
[[key1: {StreamData, :integer}, key2: {StreamData, :integer}]]}
]
defstruct foo: 42, bar: [], baz: %{}
@impl MyStruct.Coercible
def coerce_foo(value) when is_integer(value), do: {:ok, value}
def coerce_foo(value) when is_float(value), do: {:ok, round(value)}
def coerce_foo(value) when is_binary(value) do
case Integer.parse(value) do
{value, ""} -> {:ok, value}
_ -> {:error, "#{value} is not a valid integer value"}
end
end
def coerce_foo(value),
do: {:error, "Cannot coerce value given for `foo` field (#{inspect(value)})"}
@impl MyStruct.Validatable
def validate_foo(value) when value >= 0, do: {:ok, value}
def validate_foo(_), do: {:error, ":foo must be positive"}
@impl MyStruct.Validatable
def validate_bar(value), do: {:ok, value}
@impl MyStruct.Validatable
def validate_baz(value), do: {:ok, value}
end
```
The above would allow the following to be done with the structure:
```elixir
s = %MyStruct{}
put_in s, [:foo], :forty_two
#⇒ %MyStruct{foo: :forty_two, bar: [], baz: %{}}
for i <- [1, 2, 3], into: s, do: i
#⇒ %MyStruct{foo: 42, bar: [1, 2, 3], baz: %{}}
Enum.map(s, &elem(&1, 1))
#⇒ [42, [], %{}]
MyStruct.__generator__() |> Enum.take(3)
#⇒ [
# %MyStruct{bar: [], baz: %{key1: 0, key2: 0}, foo: -1},
# %MyStruct{bar: ["g", "xO"], baz: %{key1: -1, key2: -2}, foo: 2},
# %MyStruct{bar: ["", "", ""], baz: %{key1: -3, key2: 1}, foo: -1}
# ]
```
### Coercion
When `coercion: true | [key()]` is passed as an argument to `use Estructura`,
the nested behaviour `Coercible` is generated and the target module claims to implement it.
To make a coercion work with `MyStruct.put/3` and `put_in/3` provided
by `Access` implementation, the consumer module should implement `MyStruct.Coercible`
behaviour.
For the consumer convenience, the warnings for not implemented functions will be issued by compiler.
### Validation
When `validation: true | [key()]` is passed as an argument to `use Estructura`,
the nested behaviour `Validatable` is generated and the target module claims to implement it.
To make a validation work with `MyStruct.put/3` and `put_in/3` provided
by `Access` implementation, the consumer module should implement `MyStruct.Validatable`
behaviour.
For the consumer convenience, the warnings for not implemented functions will be issued by compiler.
### Generation
If `generator` keyword argument has been passed, `MyStruct.__generate__/{0,1}` can be
used to generate instances of this struct for `StreamData` property based tests.
```elixir
property "generation" do
check all %MyStruct{foo: foo, bar: bar, baz: baz} <- MyStruct.__generator__() do
assert match?(%{key1: v1, key2: v2} when is_integer(v1) and is_integer(v2), baz)
assert is_integer(foo)
assert is_binary(bar)
end
end
```
### Lazy
If `access: :lazy` is passed as an option, the struct content might be instantiated lazily,
upon first access through `Kernel.×××_in/{2,3}` family.
This might be explicitly helpful when the real content requires a significant time
to load and/or store. Consider the full response from the web server, including
the gzipped content, which might in turn be a huge text file. Or an attachment to an email.
Instead of unarchiving the content, one might use `Lazy` as
```elixir
defmodule Response do
@moduledoc false
use Estructura, access: :lazy
def extract(file), do: {:ok, ZipHelper.unzip(file)}
defstruct __lazy_data__: nil,
file: Estructura.Lazy.new(&Response.extract/1)
end
response = %Response{__lazy_data__: zipped_content}
# immediate response
response |> get_in([:file])
# unzip and return
{unzipped, struct_with_cached_value} = response |> pop_in([:file])
# unzip and return the value, alter the struct with it
```
See `Estructura.Lazy` for details and options, see `Estructura.LazyMap` for
the implementation of lazy map.
"""
use Boundary
@doc false
defmacro __using__(opts) do
quote do
@__estructura__ struct!(Estructura.Config, unquote(opts))
@before_compile {Estructura.Hooks, :inject_estructura}
if @__estructura__.access == :lazy and
is_nil(Enum.find(Module.get_attribute(__MODULE__, :derive), &match?({Inspect, _}, &1))) do
@derive {Inspect, except: [:__lazy_data__]}
end
end
end
end
