[erlang-questions] Why can't I use array:size in a guard in a method?
Sun Jul 28 00:02:53 CEST 2013
On 2013-07-27 20:22, Yves S. Garret wrote:
> The code:
> printArray(Array, Size, IndexToStartWith)
> when array:size(Array) > IndexToStartWith ->
> io:format("~w~n", [array:get(IndexToStartWith, Array)]),
> printArray(Array, Size, IndexToStartWith + 1).
> The error:
> > c(arrays_example).
> arrays_example.erl:23: illegal guard expression
> Why not? I could pass the size of the array along (hence the Size
> variable), but why not procure
> the length in the guard on the fly?
You can't use any remote calls (m:f(...)) in a guard. Guards must be
side effect free, and if the function is in another module, the compiler
can't guarantee that (in particular considering that the other module
could be replaced at runtime with code that does something completely
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