Defguardm that can take multiple arguments?

Questions / Help
1

Would having defguardm that can take multiple arguments be useful ? I am writing a small db wrapper and there are multiple functions that take similar sets of arguments but not sure how frequent this use case would be in general.

2

What would its usage look like? As far as I am aware you can define guards with multiple arguments today.

3 
defguard are_blah(arg1, arg2) when is_atom(arg1) and is_map(arg2)

def foo(arg1, arg2) when are_blah(arg1, arg2) do
...
end

def bar(arg1, arg2) when are_blah(arg1, arg2) do
...
end
4

You could just pass a tuple to defguard/1 like so:

defguard are_blah(values) when is_tuple(values)
    and elem(values, 0) |> is_atom()
    and elem(values, 1) |> is_map()

def foo(arg1, arg2) when are_blah({arg1, arg2}) do
...
end

def bar(arg1, arg2) when are_blah({arg1, arg2}) do
...
end

I tested this with a tuple but I think you could probably use a map, keyword list, or any other term.

1 Like
5

thnx good point

6

This works as is:

iex(1)> defmodule M do
...(1)> defguard g(a1, a2) when is_atom(a1) and is_map(a2)
...(1)> def foo(a1, a2) when g(a1, a2), do: true
...(1)> def foo(_, _), do: false
...(1)> end
{:module, M,
 <<70, 79, 82, 49, 0, 0, 6, 212, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 0, 195,
   0, 0, 0, 22, 8, 69, 108, 105, 120, 105, 114, 46, 77, 8, 95, 95, 105, 110,
   102, 111, 95, 95, 6, 109, 97, 99, 114, ...>>, {:foo, 2}}
iex(2)> M.foo(:atom, %{})  
true
iex(3)> M.foo(:atom, :atom)
false
2 Likes
7

Dah I guess had some error when was trying it out it does work thanx