On 2/7/12 4:31 PM, Graydon Hoare wrote:
Really? I think our concept quite closely mirrors most languages that
mix mutable and immutable types. Either can nest in either, and saying
something is mutable or immutable is only a statement about one level
of nesting.
I agree that we mirror existing languages, but I disagree that this
makes it safe. Most languages with which I'm familiar, like O'Caml,
don't have this issue because they do not have interior record types.
Languages which do, namely C++, have special rules.
For example, in C++ you cannot have a const field of value type unless
all fields within that type are const. Compiling this program in gcc,
for example:
struct foo { const int x; };
struct bar { foo f; };
void test(bar *b, foo f) {
b->f = f;
}
yields the following error: "non-static const member ‘const int foo::x’,
can't use default assignment operator".
Niko
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