# Extructure

Extructure is a flexible destructure library for Elixir.

By default the library is using loose (flexible) matching, allowing for implicit structural conversions (maps,
lists and tuples, from one to another). Tuple and list key pair element order are also taken loosely by default.   

Toggling from loose to Elixir-default ("rigid") mode is done via the `^` operator.

Optional variables are also supported with or without a default value.

## Installation

```elixir
def deps do
  [
    { :extructure, "~> 0.1.0"}
  ]
end
```

Import the Extructure module in every module where you use it:
```elixir
defmodule Foo do
  # uses, aliases, and imports
  import Extructure
  
  # ..
end
```

## Docs

The docs can be found at [HexDocs](https://hexdocs.pm/extructure).

## Sample usage

#### Fetching two mandatory variables and one optional from the LiveView assigns

Assuming a map of socket assigns, a standard pattern matching followed by retrieving an optional value as shown below:

```elixir
%{
  first_name: fist_name,
  last_name: last_name,
} = socket.assigns

age = socket.assigns[ :age]
```

is a one-liner in Extructure:

```elixir
%{ first_name, last_name, _age} <~ socket.assigns
```

#### Implicit transformation between maps, lists and tuples with key pairs

Given the Extructure's loose treatment of structures in terms of their interchangeability, the former can be expressed
in a more readable manner: 

```elixir
{ first_name, last_name, _age} <~ socket.assigns
```

or 

```elixir
[ first_name, last_name, _age] <~ socket.assigns
```

#### Default values

An optional variable can be written as a function taking zero or one arguments, with a single argument being the default
value, and/or as the variable name prefixed with a single underscore character `_`.

```elixir
[ first_name, last_name, age( 25)] <~ socket.assigns
```
or

```elixir
[ first_name, last_name, _age( 25)] <~ socket.assigns
```

#### Flexible keyword list and tuple of key pairs size and element order

```elixir
[ b, a] <~ [ a: 1, b: 2, c: 3]
# => [ b: 2, a: 1]

{ b, a} <~ { { :a, 1}, { :b, 2}, { :c, 3}}
# => { { :b, 2}, { :a, 1}}  
```

#### Enforcing "rigid" (Elixir default) matching of the structures   

The rigid approach is useful to ensure the Elixir-like matching of the right side, and necessary if deconstructing
standard Elixir tuples.

```elixir
^{ a, b, c} <~ { 1, 2, 3}
# ok

^{ b, a} <~ { { :a, 1}, { :b, 2}, { :c, 3}}
# error

^[ b, a] <~ [ a: 1, b: 2, c: 3]
# error 

^%{ a} <~ %{ a: 1, b: 2}
# ok
```

#### Nesting

Any level of nesting is supported, and with the `^` operator toggling from loose to rigid and vice versa, any matching
combination can be achieved.

Ex from the `extructure_test.ex`:

```elixir
%{ a, b: b = ^{ c, d, ^%{ e}}} <~ [ a: 1, b: { 3, 4, [ e: 5]}]
assert a == 1
assert b == { 3, 4, %{ e: 5}}
assert c == 3
assert d == 4
assert e == 5
```

## Limitations

#### Optional variables and default values

The original idea was to use the standard `\\` operator to denote optional and default values in lists, tuples, and 
maps, but, as shown below, the Elixir parser does not support this expression in maps.

```elixir
[ a, b \\ nil] # ok
{ a, b \\ nil} # ok
%{ a, b \\ nil} # syntax error
```

So, decision was made that, until there's a progress with the Elixir parser, the underscore prefixed variable names will
be used for optional variables defaulting to nil, and function (macro) call syntax will be used for the optional
variables defaulting to nil or any other value, e.g.:

```elixir
%{ _a} # optional variable, defaults to nil
%{ a()} # ditto
%{ a( 25)} # optional variable, defaults to 25 
%{ _a( 25)} # ditto
```

The above syntax is used uniformly with all three types (maps, lists, tuples).           

The limitation that comes with this approach is that there can't be macro calls placed within the left-side expression.

Should the Elixir core team decide to remove the parser restriction, a support for the standard Elixir optional
variables (arguments) would be added and the present notation would be slowly phased out (leaving it to the
compatibility mode).  

## Formatting

The source code formatting in this library diverges from the standard formatting practice based on using `mix format`
in so much that there's a leading space character inserted before each initial argument / element with an intention to
improve the code readability (subject to the author's personal perception).

Another detail diverging from the standard Elixir formatting is that, where present, multi-line function signatures
and `with` statements will not have the `do` at the end of the last of the lines but, instead, indented in the new
line, e.g.:

```elixir
with { _, foo} <- get_foo( a, b, c),
     { _, bar} <- foo_to_bar( foo)
  do
  # logic
else
  _ ->
    x    
end
```

The preferred width is 120 characters for the code and 80 characters for the docs.