问题
I need help regarding understanding the following syntaxes in elixir !, ?, _, and ..
What's those syntaxes role in elixir's function? For example Repo.get!.
I'm not sure whether they were just function name, or has a role. Though I know . is for calling anonymous function. And _ for any or variadic?
回答1:
! - 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).
回答2:
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)
来源：https://stackoverflow.com/questions/32449423/whats-the-meaning-of-and-syntax-in-elixir