Construct v2.1.10 Construct behaviour View Source

Construct internally divided into three components:

Construct — defining structures;
Construct.Cast — making structure instances;
Construct.Type — type-coercion and custom type behaviour.

Construct definition

defmodule StructureName do
  use Construct, struct_opts

  structure do
    include AnotherStructure
    field name, type, options
  end
end

struct_opts is options passed to make/2 and make!/2, described in Construct.Cast.make/3.

When you type use Construct — library bootstrapped few functions with Construct behaviour:

make/2 — just an alias to Construct.Cast.make/3;
make!/2 — alias to make/2 but throws Construct.MakeError exception if provided params are invalid;
cast/2 — alias to make/2 too, for follow Construct.Type behaviour and use defined structure as type.

Link to this section Summary

Types

t()

Functions

construct_definition?(module)

Checks if provided module is Construct definition

field(name, type \\ :string, opts \\ [])

Defines field on the structure with given name, type and options

include(struct, opts \\ [])

Includes provided structure and checks definition for validity at compile-time

structure(list)

Defines a structure

types_of!(module)

Collects types from defined Construct module to map

Callbacks

cast(params, opts)

Alias to make/2, used to follow Construct.Type.cast/1 callback

make!(params, opts)

Alias to make/2, but raises an Construct.MakeError exception if params have errors

make(params, opts)

Alias to Construct.Cast.make/3

Link to this section Types

t()

t() :: struct()

Link to this section Functions

construct_definition?(module)

Checks if provided module is Construct definition

field(name, type \\ :string, opts \\ []) (macro)

field(atom(), Construct.Type.t(), Keyword.t()) :: Macro.t()

Defines field on the structure with given name, type and options.

Checks definition validity at compile time by name, type and options. For custom types checks for module existence and Construct.Type.cast/1 callback.

If field definition is invalid for some reason — it throws an Construct.DefinitionError exception with detailed reason.

Options

:default — sets default value for that field:
- The default value is calculated at compilation time, so don’t use expressions like DateTime.utc_now or Ecto.UUID.generate as they would then be the same for all structures;
- Value from params is compared with default value before and after type cast;
- If you pass field :a, type, default: nil and make(%{a: nil}) — type coercion will not be used, nil compares with default value and just appends that value to structure;
- If field doesn’t exist in params, it will use default value.
By default this option is unset. Notice that you can’t use functions as a default value.

include(struct, opts \\ []) (macro)

include(t(), keyword()) :: Macro.t()

Includes provided structure and checks definition for validity at compile-time.

Options

:only - (integer) specify fields that should be taken from included module, throws an error when field doesn’t exist in provided module.

If included structure is invalid for some reason — this macro throws an Construct.DefinitionError exception with detailed reason.

structure(list) (macro)

Defines a structure.

types_of!(module)

Collects types from defined Construct module to map

Link to this section Callbacks

cast(params, opts)

cast(params :: map(), opts :: Keyword.t()) :: {:ok, t()} | {:error, term()}

Alias to make/2, used to follow Construct.Type.cast/1 callback.

To use this structure as custom type.

make!(params, opts)

make!(params :: map(), opts :: Keyword.t()) :: t()

Alias to make/2, but raises an Construct.MakeError exception if params have errors.

make(params, opts)

make(params :: map(), opts :: Keyword.t()) :: {:ok, t()} | {:error, term()}

Alias to Construct.Cast.make/3.