helicon
Using macros in guard clauses
Hey!
I have a function
@doc """
Check if given id has 64-bit size
Examples:
> MyModule.has_64_bit_size(132700114308300801)
true
> MyModule.has_64_bit_size(35)
false
"""
def has_64_bit_size(id) do
bit_size(:binary.encode_unsigned(id)) == 64
end
I want to implement defmacro has_64_bit_size. What should it look like?
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hauleth
You do not need such magic value:
defguard at_most_64(num) when :erlang.band(num, :erlang.bsl(0xff, 56)) != 0 and num < :erlang.bsl(1, 64)
LostKobrakai
Guards can only be composed of guard-safe functions and also with elixir >= 1.6 you want to use defguard instead of a macro to compose those. :binary.encode_unsigned/1 is not guard-safe though, so you cannot do what you want to do in a guard.
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