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An error will be generated when operator is used on a literal, anonymous function or table constructor

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This commit is contained in:
Vyacheslav Egorov 2021-06-09 15:29:40 +03:00
parent 4e139dd295
commit 79baa9caa8
1 changed files with 8 additions and 7 deletions
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15
rfcs/syntax-nil-forgiving-operator.md
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@ -43,6 +43,13 @@ primaryexp ::= prefixexp [`!'] { postfixeexp }
When we get the `!` token, we will wrap the expression that we have into a new AstExprNonNilAssertion node.
An error is generated when the type of expression node this is one of the following:
* AstExprConstantBool
* AstExprConstantNumber
* AstExprConstantString
* AstExprFunction
* AstExprTable
This operator doesn't have any impact on the run-time behavior of the program, it will only affect the type of the expression in the typechecker.
---
@ -54,7 +61,7 @@ p.a! = b
```
---
When operator is used on expression of a union type with a 'nil' option, it removes that option from the set.
When operator is used on expression of a union type with a `nil` option, it removes that option from the set.
If only one option remains, the union type is replaced with the type of a single option.
If the type is `nil`, typechecker will generate a warning that the operator cannot be applied to the expression.
@ -68,9 +75,3 @@ As an example from Roblox, instance path could dynamically change from being kno
## Drawbacks
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, like use of the operator on constants, but the check will require an AST match:
```lua
local a = 2!
local b = "str"!
```