digitalmars.D.bugs - [Issue 13006] New: Allow inout return type without inout parameters
- via Digitalmars-d-bugs (50/50) Jun 29 2014 https://issues.dlang.org/show_bug.cgi?id=13006
https://issues.dlang.org/show_bug.cgi?id=13006 Issue ID: 13006 Summary: Allow inout return type without inout parameters Product: D Version: D2 Hardware: All OS: All Status: NEW Severity: enhancement Priority: P1 Component: DMD Assignee: nobody puremagic.com Reporter: k.hara.pg gmail.com Currently unique expressions can be converted to arbitrary type qualifier. int * mp = new int(1); immutable(int)* ip = new int(1); But, currently we cannot define a function that returns unique expression without pure attribute. int* foo() pure { return new int(1); } int * mp = foo(); // OK immutable(int)* ip = foo(); // OK int* bar() { return new int(1); } int * mp = bar(); // OK immutable(int)* ip = bar(); // NG! I think it is possible by the subject proposal. inout(int)* bar1() { return new int(1); } int * mp = bar1(); // could be possible immutable(int)* ip = bar1(); // could be possible inout(int)* bar2() { inout(int)* p = new int(1); // <-- propagate expression uniqueness via inout qualifier return p; } int * mp = bar2(); // could be possible immutable(int)* ip = bar2(); // could be possible In my thought, there's some assumptions as follows. 1. Unique expressions (eg. new int(1)) could be converted to arbitrary type qualifier, so it should be convertible to inout type. 2. If inout type appears on return type without inout parameter, it would be converted to arbitrary type qualifier without restrictions from function argument types. My proposal have some pros: 1. Some limitations about inout type qualifier could be lifted. For example, isInputRange definition would be simplified. 2. Unique expressions could be more useful in D. By using inout, we can propagate it in function body. and cons: 1. We should have a way to copy inout objects - eg. qualified postblit feature (DIP49) is necessary. --
Jun 29 2014