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On Saturday, 30 March 2024 at 09:24:12 UTC, Nick Treleaven wrote:
>On Saturday, 30 March 2024 at 03:00:32 UTC, Walter Bright wrote:
>On 3/22/2024 3:51 AM, Nick Treleaven wrote:
>I think this is workable without DFA, the compiler just tracks when a variable is initialized. There is never a state where a variable may be both initialized and not initialized
A a = null;
if (i)
a = new A();
// a is both initialized and not initialized
There a is always initialized. It's a nullable type. If you remove the = null and make a a non-nullable type, you would get an error for the if statement because it initializes a in its branch, and there is no else branch which is required to also initialize a.
This is an example for Herb Sutter's cppfront, which enforces that p is non-null:
main: () =
{
i := 0;
p: unique_ptr<int>;
if (i) {
p = new<int>; // error: p must be initialized on both branches or neither
}
}
Now throw in loops and goto's, and DFA is needed. Compiler optimizers use DFA because it works and ad-hoc techniques do not.
cppfront:
main: () =
{
i := 0;
p: unique_ptr<int>;
while i < 3 next i++ {
p = new<int>;
std::cout << p* << "\n"; // ok, p is always initialized
}
}
Changing the while loop:
while i < 3 next i++ {
std::cout << p* << "\n"; // error, p used before it was initialized
p = new<int>;
}
Goto skipping initialization is already disallowed in D.
>This does not need DFA, correct?
