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Added design for operator use on l-values that will generate a parse error

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This commit is contained in:
Vyacheslav Egorov 2021-06-09 15:03:41 +03:00
parent 28b0208437
commit 5429b7ba11
1 changed files with 9 additions and 5 deletions
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14
rfcs/syntax-nil-forgiving-operator.md
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@ -45,6 +45,14 @@ When we get the `!` token, we will wrap the expression that we have into a new A
This operator doesn't have any impact on the run-time behavior of the program, it will only change the type of the expression in the typechecker.
---
While parsing an assignment expression starts with a *primaryexp*, it performs a check that it has an l-value based on a fixed set of AstNode types.
Since using `!` on an l-value has no effect, we don't extend this list with the new node and will generate a specialized parse error for code like:
```lua
p.a! = b
```
---
If the operator is used on expression of type that is already non-nil, it has no effect and doesn't generate additional warnings.
@ -56,11 +64,7 @@ As an example from Roblox, instance path could dynamically change from being kno
It might be useful to warn about unnecessary uses of this operator, but we have no way way of enabling this behavior.
It may be possible to warn for some limited number of cases, for example, when used on l-value:
```lua
p.a! = b
```
Another case is for constants, but the check will require an AST match:
It may be possible to warn for some limited number of cases, like use of the operator on constants, but the check will require an AST match:
```lua
local a = 2!
local b = "str"!