On Saturday, 17 March 2012 at 17:59:12 UTC, Andrei Alexandrescu
wrote:
On 3/17/12 12:02 PM, markusle wrote:
Using dmd 2.058 I can compile the following
pure bool has_path(string paths[], string needle) {
paths[0] = "bad";
... do something else ...
return false;
}
and change the passed in array "paths". Isn't this a violation
of
has_path's pure contract? Shouldn't all pure function
parameters
be passed as "in" to avoid side effects. Sorry if I missed
something obvious.
D's working definition of a pure function is "effect only
depends on parameters". Mutating parameters does fit the
definition.
This is less tight than other languages' definition, but we
believe it's a sweet spot between reaping the modularity
benefits of purity, and benefiting of the advantages of
mutation.
Also, not all is lost. If you want to disallow parameter
mutation, add "in" to them. That way, you only need to see the
function's signature to draw a variety of interesting facts
about it.
Andrei
Thanks a lot for yours and Adam's detailed explanation. This
makes much more sense now.
