What's the meaning of "!", "?", "_", and "." syntax in elixir
!
- Convention for functions which raise exceptions on failure.
?
- Convention for functions which return a boolean value
_
- Used to ignore an argument or part of a pattern match expression.
.
- As you mentioned is used for calling an anonymous function, but is also used for accessing a module function such as Mod.a(arg)
.
Firstly ! and ?
They are naming conventions usually applied to the end of function name and are not any special syntax.
! - Will raise an exception if the function encounters an error.
One good example is Enum.fetch!(It also has a same Enum.fetch which does not raise exception).Finds the element at the given index (zero-based). Raises OutOfBoundsError if the given position is outside the range of the collection.
? - Used to show that the function will return a boolean value, either true or false. One good example is Enum.any? that returns true if functions is true for any value, otherwise return false
_
- This will ignore an argument in function or in pattern matching. If you like you can give a name after underscore.Ex - _base
This is commonly used in the end of a tail recursive function. One good example is the power function. If you want to raise any number base to 0 the result it 1, so it really does not matter what base is
defp getPower(_base,0), do: 1
.
- Used to access any function inside the module or as you suggested calling an anonymous function
iex(1)> square = fn(number) -> number * number end
iex(2)> square.(4)