Long story short, you can’t check for blank strings in a guard, as you had to iterate over the string to do so, and that’s not possible.
NobbZ
dimitarvp
Exadra37
Sorry but I am not seeing what it’s the advantage or I am not getting what you are suggesting.
If what you suggest is to inject the three empty?/1 via a macro and then use it in the body of the function, then that’s just a different way of achieving what I already do, isn’t?
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NobbZ
Exadra37
Remote call from a guard?
I am assuming you mean this:
def my_func(string) when not UtilsModule.empty?(string) do
# do stuff
end
0
NobbZ
Remote calls from a guard are not possible, though calling your function can’t be called from a guard anyway. That’s why I am confused.
1
Exadra37
Yes I know remote calls are not possible from a guard clause, and that it’s why I wrote this post to ask how I could write a guard to check for a blank string, and in the first post I have the example of the macro I tried to build.
The other example in a subsequent post shows how I am checking for a blank string in the body of a function, and it’s there just to illustrate how I have to repeat this code every time i need to check for the blank string.
In my opinion would be nice that once the language doesn’t support the check in the core, that at least would let me build my own guard, but it seems to be a mission impossible unless the core of Elixir one day supports it or allow the developer to build it’s own true guard clause, because now it seems to me that a custom guard clause naming is misleading, because it only allow us to group togetther other guard clauses.
0
NobbZ
Not beeing able to write this guard is much deeper than elixir, it’s a limitation of the BEAM, which only allows for a handful of whitelisted functions.
And I still do not understand why you have to repeat your function everywhere, you have to define it once and call it everywhere…
0
Exadra37
I am not defining it everywhere I want to use it, I jsut don’t want to call it from the body everywhere…
See example usage from above:
As you can see I am just doing the remote call as you suggested, and this is precisely what I was trying to avoid by having a guard to check for the blank string.
0
cenotaph
Late to the discussion, just facing the same issues and wanted to update with the documentation. Maybe things have changed since the posting of this!
Such a guard would look like this:
def my_function(number) when is_integer(number) and rem(number, 2) == 0 do
# do stuff
end
It would be repetitive to write every time we need this check. Instead you can use defguard/1 and defguardp/1 to create guard macros. Here’s an example how:
defmodule MyInteger do
defguard is_even(term) when is_integer(term) and rem(term, 2) == 0
end
and then:
import MyInteger, only: [is_even: 1]
def my_function(number) when is_even(number) do
# do stuff
end
While it’s possible to create custom guards with macros, it’s recommended to define them using defguard/1 and defguardp/1 which perform additional compile-time checks.
2