Bug 14854 – @disable this inconsistent between structs and classes

This code class C1 { @disable this() {} } class C2 { @disable this(); } struct S1 { @disable this() {} } struct S2 { @disable this(); } void main() { } results in this compilation error: q.d(13): Error: constructor q.S1.this default constructor for structs only allowed with @disable and no body For structs, it's clearly required that @disable this() not have a body, whereas for classes, for some reason, the compiler doesn't care. The error message does explicitly use the word struct, which implies that this difference is intentional, but I don't see any reason to allow for the inconsistency. It just makes it less obvious, which syntax you should be using. And in general, I don't see any reason to allow bodies on @disabled functions. One interesting side effect of putting a body on the @disabled default constructor on a class is that it actually affects the code coverage analyzer, because the lines inside the body never run and count as uncovered. So, I suggest that we deprecate having bodies on _all_ @disabled functions and move to making it an error like it is with @disabling the init property on a struct.

Hello! So the solution that you suggest is to make the compiler give an error when the @disabled is used? If so, do you think that this will impact some code somewhere else? I think that I will be able to write a fix for this.

My suggestion is to make it an error when @disable is used on a function with a body - just like happens right now when you do it with @disable this() {} on a struct. I can't think of any reason why this would be a problem. Certainly, I don't see why it would ever make sense to declare an @disabled function with a body. By definition, it's unreachable. However, it will need to be done as a deprecation first in case anyone does have code that has @disable on a function with a body (like in the example here with a class).

@tibi77 created dlang/dmd pull request #9413 "Fix Issue 14854 - @disable this inconsistent between structs and classes" fixing this issue: - Fix Issue 14854 - @disable this inconsistent between structs and classes https://github.com/dlang/dmd/pull/9413

@tibi77 created dlang/phobos pull request #6893 "Remove redundant body of @disable functions. Issue 14854 DMD" mentioning this issue: - Remove redundant body of @disable functions. Issue 14854 DMD https://github.com/dlang/phobos/pull/6893

dlang/phobos pull request #6893 "Remove redundant body of @disable functions. Issue 14854 DMD" was merged into master: - 336047098929c141f2fdd7b00c25d0aec3abedda by Lepadatu Tiberiu: Remove redundant body of @disable functions. Issue 14854 DMD https://github.com/dlang/phobos/pull/6893

@Mai-Lapyst created dlang/dmd pull request #15052 "Fix issue 14854 - @disable this inconsistent between structs and classes" fixing this issue: - Fix issue 14854 - @disable this inconsistent between structs and classes https://github.com/dlang/dmd/pull/15052

Closing as per: https://github.com/dlang/dmd/pull/15052#pullrequestreview-1366507833