RFC: Implementation of binary assignment operators (e.g s.x += 2) for @property functions

[Michael V. Franklin via Digitalmars-d]

An implementation of binary assignment operators for @property 
functions has been submitted to the DMD pull request queue at 
https://github.com/dlang/dmd/pull/7079.  It addresses the 
following issues:

Issue 8006 - Implement proper in-place-modification for properties
https://issues.dlang.org/show_bug.cgi?id=8006
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This is the primary issue motivating the pull request.  The pull 
request is only a partial resolution of this issue; it implements 
binary assignment operators (e.g. `s.x += 2`), but not unary 
assignment operators (e.g. `s.x++`).  The plan is to implement 
unary assignment operators in a separate pull request after the 
fate of the binary assignment operators pull request is decided.

Issue 18187 – std.bitmap fields should be lvalues
https://issues.dlang.org/show_bug.cgi?id=16187
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This is a more real-world example where binary assignment 
operators would be beneficial, as bit fields are not individually 
addressable.

Issue 15231 - opOpAssign allows assignment to rvalue
https://issues.dlang.org/show_bug.cgi?id=15231
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While the pull request does not actually resolve the error 
illustrated in this issue, it demonstrates how a user desired 
binary assignment operators for @property functions so much that 
(s)he attempted to implement them indirectly by modeling the 
value type as a struct and overloading its operators.  Had binary 
assignment operators been implemented the user probably would not 
have had any need expend such effort.

Like the other users that commented in the issues above, I was a 
bit dismayed to discover that binary assignment operators were 
not implemented for @property functions.  When I submitted the 
pull request I was under the assumption that the only reason they 
weren’t implemented was because noone had gotten around to it yet.

Walter has requested that I make this forum post to inform the 
community of this change in an effort to discuss its merits 
and/or shortcomings.

We ask for your comments whether they be in approval or 
disapproval of this pull request so we can determine the best way 
forward.

Thank you,
Michael V. Franklin