SumType allows this bit of code: ``` SumType!(int, string) st; st.match!( function ref int(string _) => assert(0), function ref int(ref int i) => i, ); ``` However, it does not allow returning a pointer to i: ``` SumType!(int, string) st; st.match!( function ref int*(string _) => assert(0), function ref int*(ref int i) => &i, ); ``` This is because `canMatch` does not account for `ref`. The template `valueTypes` stores all types of the member values and uses SumTypes's `get` function, which returns a `ref`. However, ref does not persist and the type is not sent to `canMatch` as a `ref`.
Because of this, when matching, `canMatch` will fail as it will test for a copy, and returning a reference of that value results in escaping it.
@iK4tsu created dlang/phobos pull request #8457 "Issue 23101 - [std.sumtype] canMatch does not account ref " fixing this issue: - fix(sumtype): template canMatch does not account for ref when matching The template `canMatch` does not account for `ref`. The template `valueTypes` stores all types of the member values and uses SumTypes's `get` function, which returns a `ref`. However, ref does not persist and the type is not sent to `canMatch` as a `ref`. Because of this, when matching, `canMatch` will fail as it will test for a copy, and returning a reference of that value results in escaping it. Fix Issue 23101 Signed-off-by: João Lourenço <jlourenco5691@gmail.com> https://github.com/dlang/phobos/pull/8457
Sorry, correction of the bug report example: ``` SumType!(int, string) st; st.match!( function int*(string _) => assert(0), function int*(ref int i) => &i, ); ```
dlang/phobos pull request #8457 "Issue 23101 - [std.sumtype] canMatch does not account ref " was merged into master: - 6069c449303e8571b7b73c4fe50fc3088832d5fe by João Lourenço: fix(sumtype): template canMatch does not account for ref when matching The template `canMatch` does not account for `ref`. The template `valueTypes` stores all types of the member values and uses SumTypes's `get` function, which returns a `ref`. However, ref does not persist and the type is not sent to `canMatch` as a `ref`. Because of this, when matching, `canMatch` will fail as it will test for a copy, and returning a reference of that value results in escaping it. Fix Issue 23101 Signed-off-by: João Lourenço <jlourenco5691@gmail.com> https://github.com/dlang/phobos/pull/8457