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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?
236
We use it to match any variable and discard it, because Elixir considers it permanently unbound: iex(38)> _ ** (CompileError) iex:38: unbound variable _ But when I assign something to underscore, the value gets echoed the same way it does in the case of normal variable binding: iex(38)> x = 10 10 iex(39)> _ = 10 10.
A trailing bang (exclamation mark) signifies a function or macro where failure cases raise an exception.
Starting in elixir 1.2 there is an i command in iex that will list the type and more of any Elixir variable. If you look in the code for the i command you'll see that this is implemented via a Protocol.
We can define functions with names so we can easily refer to them later. Named functions are defined within a module using the def keyword. Named functions are always defined in a module. To call named functions, we need to reference them using their module name.
! - 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).
151
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)
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