Correct precedence of the null-conditional operators #18037
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pkulikov
commented
Apr 24, 2020
| | --------- | ---------------- | | ||
| | [x.y](member-access-operators.md#member-access-expression-), [f(x)](member-access-operators.md#invocation-expression-), [a[i]](member-access-operators.md#indexer-operator-), [x++](arithmetic-operators.md#increment-operator-), [x--](arithmetic-operators.md#decrement-operator---), [x!](null-forgiving.md), [new](new-operator.md), [typeof](type-testing-and-cast.md#typeof-operator), [checked](../keywords/checked.md), [unchecked](../keywords/unchecked.md), [default](default.md), [nameof](nameof.md), [delegate](delegate-operator.md), [sizeof](sizeof.md), [stackalloc](stackalloc.md), [x->y](pointer-related-operators.md#pointer-member-access-operator--) | Primary | | ||
| | [+x](arithmetic-operators.md#unary-plus-and-minus-operators), [-x](arithmetic-operators.md#unary-plus-and-minus-operators), [\!x](boolean-logical-operators.md#logical-negation-operator-), [~x](bitwise-and-shift-operators.md#bitwise-complement-operator-), [++x](arithmetic-operators.md#increment-operator-), [--x](arithmetic-operators.md#decrement-operator---), [^x](member-access-operators.md#index-from-end-operator-), [x?.y](member-access-operators.md#null-conditional-operators--and-), [x?[y]](member-access-operators.md#null-conditional-operators--and-), [(T)x](type-testing-and-cast.md#cast-expression), [await](await.md), [&x](pointer-related-operators.md#address-of-operator-), [*x](pointer-related-operators.md#pointer-indirection-operator-), [true and false](true-false-operators.md) | Unary | | ||
| | `x?.y`, `x?[y]` | [Null-conditional operators](member-access-operators.md#null-conditional-operators--and-) | |
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@BillWagner the more I think, the more I see that the following three solutions might make sense for the precedence table:
- bring
?.and?[]back to the first row (pro: it's the same precedence as they are unary post-fix; con: null-conditional operators are not primary (however, we can change the name of the first row from "primary" to "primary and null-conditional") - place
?.and?[]into the separate row as the current PR does - remove
?.and?[]from the precedence table at all (for example, the spec doesn't mention the precedence of?.and?[]explicitly)
What do you think?
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Placing just ?. and ?[] in a separate row is not correct. Option 1 is clearly better as it does not introduce more confusion.
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@BillWagner I've updated the table as per comment
pkulikov
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BillWagner
approved these changes
Apr 28, 2020
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Thanks for participating in all the conversations on this issue and PR @pkulikov
I'll 
now.
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By this comment the null-conditional operators behave as if their precedence is higher than one of unary operators. I guess that's true because the null-conditional operators are post-fix, and post-fix operators precede pre-fix operators. Still,x?.yandx?[y]are not primary expressions. Thus, the separate row for them.Update: partially reverts #18001 (the null-conditional operators changes)