Bug 6553 – Better const(char[]) !-> string error message

This is related to bug 5081 , see there for more context. I think the behaviours shown by this little program are correct, but I think that error message needs to be improved (completed with more details), because in some cases (like foo1) that's an acceptable operation (dmd 2.055 head): string foo1() pure { const(char[]) s2 = ['a']; return s2; } string foo2() pure { return ['a']; } string foo3(immutable char[] s) pure { return s; } string foo4(in char[] s1, immutable char[] s2) pure { return s2; } string foo5(in char[] s) pure { return s; // Error: cannot implicitly convert expression (s) of type const(char[]) to string } void main() { immutable r1 = foo1(); // OK immutable r2 = foo2(); // OK immutable r3 = foo3(['a']); // OK immutable r4 = foo4(['a'], ['b']); // OK immutable r5 = foo5(['a']); // Error } Good and complete error messages are needed to help the programmer understand her mistake and build a correct model of D semantics in her head.

All of these compile in 2.061. Got any other test-cases or should we close?

(In reply to comment #1) > All of these compile in 2.061. Got any other test-cases or should we close? Wait, the conversion in foo5 should fail correctly. If it is allowed, following code will accidentally break const-correctness. void main() { char[] buf = ['a']; immutable str = foo5(buf); assert(str[0] == 'a'); buf[0] = 'b'; assert(str[0] == 'a'); // fails!? } And this code compiles without errors in current git head. I think this is a regression. Will open a new issue.

(In reply to comment #2) > I think this is a regression. Will open a new issue. Opened: Issue 9230 - Incorrect implicit immutable conversion occurs in pure function

In general, D's type system does not allow implicit conversion from 'const(char[])' to 'string', so I'm not sure the way to provide "better" error diagnostic. So I close this issue as 'invalid'. If you have concrete example of the compiler output, please comment it and reopen this issue.