"x op= y" and a prefix increment resolve in two phases: the instance operators
reachable from the static type of x come first wherever x is a variable -
whether or not the result is used - and the static operators only if none of
them is applicable. A postfix increment whose result is used is the one form
that always binds a static operator. CallBuilder models the first phase when it
checks that recompiling an instance operator call binds the same method; the
fallback phase is deliberately not modeled, since a call the instance
candidates cannot account for must give up the operator form rather than
collide with a static operator.
The same rule cuts the other way for the folds built from static operator
calls: a shadowed fold has to be written in one of the static-binding forms.
The binary operators become "x = x + y"; an increment becomes a postfix
increment whose result goes to a discard, "_ = x++;". That form only exists as
a statement, so the folds that would embed a shadowed increment in an
expression hold back and FixRemainingIncrements gives the increment a statement
of its own instead. A foreach variable cannot be such a receiver at all (it is
read-only), so the loop keeps the existing variable as a writable copy, both
for a plain loop variable and for a deconstruction.
Assisted-by: Claude:claude-opus-5:Claude Code
Siegfried Pammer