Re: Proposal: Increasing type safety with a keyword
Hakusa@gmail.com wrote:
First, I think the keyword "explicit" already has a similar use and
could be used here, too.
Explicit is used only in constructors.
Also, keyword "only" aims to be a complete type-safe solution that scales well
from built-in types to
user-defined types.
This means that inevitably, keyword "only" will have similar effects with other
existing type-safety
facilities in C++ in specific areas (like "explicit" use in constructors).
However existing C++98/03 practice (e.g. the keyword ?explicit? in
constructors), and the new features of
C++0x (e.g. the new use of keyword ?auto?), will keep their current meanings.
Second, I think that you should have to add to your proposal that f
(int) cannot be called with an only int (explicit int). Reason? The
fallowing:
void f(int& x)
{
x = 5.4;
}
int main()
{
only int x=5;
f(x);
}
Since f will modify x in a way that violates being an only int, and
the compiler has no way of knowing this, the code is broken.
Similarly, I believe all the const correctness rules should have to
apply.
Your above code, in a completely type-safe implementation, using keyword "only":
void f(only int &x)
{
x= 5.4; // Compiler error. Type mismatch.
}
int main()
{
only int x= 5;
f(x);
}
Comment: Usually every function does not care about the code that calls it.
So if we have an unsafe function:
void f(int& x)
{
// Operations take place
}
it should work for both an "int" object, and a "only int" object. This is the
reason why we define the
function with an "int" reference as an argument, and not with an "only int"
reference as an argument.
If we want a type-safe argument, we use an "only" argument.
http://www.cpp-software.net/documents/cpp_only_proposal.html
is the proposal as it is. The document will get updated twice in every 24h.
How should virtual classes work? Your proposal should definitely
explain this.
The proposal is a work in progress, and doesn't cover yet virtual classes. If
you want to contribute any ideas
on the proposal, you are free to do so, either by posting here or sending me an
email.
Anyone who contributes to this proposal and wants to, he will receive full
credit for his contribution in the
final proposal, if the proposal gets completed.
I have sent a separate message for this.
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