Bug 15500 – default construction disabled for struct constructor with default arguments

$dmd_068_X -c -o- $bugs_D/bug_D20160102T173458.d ok DMD64 D Compiler v2.069-devel-6b2b521 dmd -c -o- $bugs_D/bug_D20160102T173458.d Error: variable a default construction is disabled for type A ---- struct A{ this(int a=0){ } } void fun(){ static A a; } ----

*** Issue 15515 has been marked as a duplicate of this issue. ***

According to Andrej it's supposed to be a warning only. https://github.com/D-Programming-Language/dmd/pull/5185#issuecomment-168821489 But the changed code triggers an error due to a disabled constructor. ---- cat > bug.d << EOF struct S { this(string r = ".") { } } void test() { S s; } EOF dmd -c -w bug ---- bug.d(2): Warning: constructor bug.S.this default constructor for structs only allowed with @disable, no body, and no parameters bug.d(7): Error: variable bug.test.s default construction is disabled for type S ----

Am I missing something? I assumed this would just be a straightforward "structs cannot have a 0-arg constructor, even by using default arguments", regardless of use. Why push the error message down to the user of the struct? Any use case of the default argument is an error, therefore the default arguement should itself be an error.

(In reply to John Colvin from comment #3) > Am I missing something? I assumed this would just be a straightforward > "structs cannot have a 0-arg constructor, even by using default arguments", > regardless of use. It is build that way, only a warning for now, but something went wrong and now there is an additional error on usage.

Commits pushed to stable at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/0122225c1eb7b4c92a5060fefbc5cae498818d39 fix Issue 15500 - default construction disabled for struct constructor with default arguments - fix implementation of #5185, the new check should only be a deprecation warning for now, but inadvertently disabled default initialization (`S s;`) by setting sd.noDefaultCtor - simplify logic and control flow (only need to check whether the first parameter has a default argument) - still allow any kind of variadic constructor (doesn't make sense to distinguish C from D-style variadics) We might deprecate those called w/ zero arguments (`auto s = S();`) on the call-site, but disallowing them in general seems to drastic. - Use a deprecation instead of a warning, since using the -dw switch as default we agreed to no longer abuse warnings for deprecations, so that people can cleanly compile with -w. Edgy people insisting on using -de have to immediately deal w/ deprecations. https://github.com/D-Programming-Language/dmd/commit/e50f8aa63356b767c713b50c4d944e9b28345de7 Merge pull request #5331 from MartinNowak/fix15500 fix Issue 15500 - default construction disabled for struct constructor with default arguments

Commits pushed to master at https://github.com/D-Programming-Language/dmd https://github.com/D-Programming-Language/dmd/commit/0122225c1eb7b4c92a5060fefbc5cae498818d39 fix Issue 15500 - default construction disabled for struct constructor with default arguments https://github.com/D-Programming-Language/dmd/commit/e50f8aa63356b767c713b50c4d944e9b28345de7 Merge pull request #5331 from MartinNowak/fix15500

*** Issue 15551 has been marked as a duplicate of this issue. ***