Ensure a value meets a custom criteria.

Provide a function that will accept a value and return a true/false result.

Options

None, a function with arity 1 must be provided.

• :function: The function to check. Should have an arity of 1 and return true/false.
• :message: Optional. A custom error message. May be in EEx format and use the fields described in "Custom Error Messages," below.

The function can be provided in place of the keyword list if no other options are needed.

Examples

iex> Vex.Validators.By.validate(2, &(&1 == 2))
:ok
iex> Vex.Validators.By.validate(3, &(&1 == 2))
{:error, "must be valid"}
iex> Vex.Validators.By.validate(["foo", "foo"], &is_list/1)
:ok
iex> Vex.Validators.By.validate("sgge", fn (word) -> word |> String.reverse == "eggs" end)
:ok
iex> Vex.Validators.By.validate(nil, [function: &is_list/1, allow_nil: true])
:ok
iex> Vex.Validators.By.validate({}, [function: &is_list/1, allow_blank: true])
:ok
iex> Vex.Validators.By.validate([1], [function: &is_list/1, message: "must be a list"])
:ok
iex> Vex.Validators.By.validate("a", [function: &is_list/1, message: "must be a list"])
{:error, "must be a list"}

iex> Vex.Validators.By.validate(
...>   "a", [function: fn (v) when is_list(v) -> :ok
...>                      (v) -> {:error, {:not_list, v}} end])
{:error, {:not_list, "a"}}
iex> Vex.Validators.By.validate(
...>   [], [function: fn (v) when is_list(v) -> :ok
...>                     (v) -> {:error, {:not_list, v}} end])
:ok

Custom Error Messages

Custom error messages (in EEx format), provided as :message, can use the following values:

iex> Vex.Validators.By.__validator__(:message_fields)
[value: "The bad value"]

An example:

iex> Vex.Validators.By.validate("blah", [function: &is_list/1, message: "<%= inspect value %> isn't a list"])
{:error, ~S("blah" isn't a list)}