On Thu, 22 Sep 2011 17:03:08 -0400, Jonathan M Davis <[email protected]>
wrote:
In any case, in order for a function to be able to have its return value
implicitly value implicitly cast to immutable, it must pure and all of
its
arguments must be immutable or implicitly convertible to immutable (or -
if
the compiler is ever improved to treat pure functions with const
parameters
and immutable arguments the same way - the requirement would be that the
function must be pure and all of its _arguments_ must be immutable or
implicitly convertible to immutable).
No, the parameter types can be const, and can accept mutable arguments.
The main point is, the return value has to be proven to be *unique*. The
only way to do this with pure functions is to prove that the result is
*not* a subset of the parameters. That's all.
Observe:
char[] foo(const(char)[] x) pure {...}
There is no way to write the body of this function such that the return
value is a substring of x. So you are guaranteed that the result is *new
memory*, and since it cannot be stored globally anywhere (per pure rules),
it's guaranteed to be unique, and should be implicitly castable to
immutable.
Even if you pass a char[] into foo.
-Steve
