28 lines
1.5 KiB
Markdown
28 lines
1.5 KiB
Markdown
# Ref Local Reassignment
|
|
|
|
In C# 7.2, we add support for rebinding the referent of a ref local variable or a ref parameter.
|
|
|
|
We add the following to the set of `assignment_operator`s.
|
|
|
|
``` antlr
|
|
assignment_operator
|
|
: '=' 'ref'
|
|
;
|
|
```
|
|
|
|
The `=ref` operator is called the ***ref assignment operator***. It is not a *compound assignment operator*. The left operand must be an expression that binds to a ref local variable, a ref parameter (other than `this`), or an out parameter. The right operand must be an expression that yields an lvalue designating a value of the same type as the left operand.
|
|
|
|
The right operand must be definitely assigned at the point of the ref assignment.
|
|
|
|
When the left operand binds to an `out` parameter, it is an error if that `out` parameter has not been definitely assigned at the beginning of the ref assignment operator.
|
|
|
|
If the left operand is a writeable ref (i.e. it designates anything other than a `ref readonly` local or `in` parameter), then the right operand must be a writeable lvalue.
|
|
|
|
The ref assignment operator yields an lvalue of the assigned type. It is writeable if the left operand is writeable (i.e. not `ref readonly` or `in`).
|
|
|
|
The safety rules for this operator are:
|
|
|
|
- For a ref reassignment `e1 = ref e2`, the *ref-safe-to-escape* of `e2` must be at least as wide a scope as the *ref-safe-to-escape* of `e1`.
|
|
|
|
Where *ref-safe-to-escape* is defined in https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.2/span-safety.md
|