On Fri, 19 Feb 2010 12:53:56 -0500, Denis Koroskin <[email protected]>
wrote:
On Fri, 19 Feb 2010 20:28:20 +0300, Steven Schveighoffer
<[email protected]> wrote:
On Fri, 19 Feb 2010 12:15:20 -0500, bearophile
<[email protected]> wrote:
Steven Schveighoffer:
It would be nice to allow this:
int[3] x = [a, b, c];
This is allowed now.
Yes, but 1) it allocates the literal on the heap and then throws it
away, and 2) it would not be allowed if array literals are only allowed
to be immutable. I'm speaking from the context assuming that array
literals are made to be immutable by default.
It just *can't* be immutable unless all the variables involved are
implicitly castable to immutable.
In the case of [a, b, c], it either doesn't compile, or is not an
immutable array. Because a, b, and c are runtime values (and potentially
different for every usage of that expression), it makes no sense to make
them immutable.
In the case of [1, 2, 3], all the items are available at compile-time, and
an immutable array can be created.
And what if I need a *mutable* array? .dup it?
Or use a library function that creates a new array from runtime-determined
elements. But this problem is already solved, we are talking about static
arrays, not dynamic arrays.
My suggestion would be to be consistent with built-in types.
That's fine for static arrays, but the crux of the matter is the syntax.
Dynamic arrays are inherently reference types. You cannot simply convert
them to and from mutable and immutable. So you either can't have the same
syntax to initialize dynamic arrays as you have to initialize static
arrays, or the compiler has to treat the literals for arrays differently
depending on usage.
There is not one type that an array literal can be that translates
correctly to dynamic, dynamic immutable, and static arrays. So the
compiler could do some magic to make the type special, but it also has to
behave differently for different uses. It's a complicated problem to
solve, and the question is, where does the solution belong, in the library
or the compiler?
-Steve
