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These changes are to improve the experience for publishing these proposals. One change should be carefully reviewed to ensure I didn't introduce any technical errors: I translated the binary literals grammar into ANTLR to match all other specs and proposals. See changes in proposals/csharp-7.0/binary-literals.md Other changes are: 1. Use consistent ATX headers, with one H1 per proposal. 1. use `csharp` as language identifier in code snippets 1. Use relative links to other markdown from the dotnet/csharplang repo. That way, when published on docs.microsoft.com, the links will resolve to the publsihed articles on the same site. (Links to content not being published are not modified.) 1. spelling / capitalization found by the lint tool.
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Throw expression
We extend the set of expression forms to include
throw_expression
: 'throw' null_coalescing_expression
;
null_coalescing_expression
: throw_expression
;
The type rules are as follows:
- A throw_expression has no type.
- A throw_expression is convertible to every type by an implicit conversion.
A throw expression throws the value produced by evaluating the null_coalescing_expression, which must denote a value of the class type System.Exception, of a class type that derives from System.Exception or of a type parameter type that has System.Exception (or a subclass thereof) as its effective base class. If evaluation of the expression produces null, a System.NullReferenceException is thrown instead.
The behavior at runtime of the evaluation of a throw expression is the same as specified for a throw statement.
The flow-analysis rules are as follows:
- For every variable v, v is definitely assigned before the null_coalescing_expression of a throw_expression iff it is definitely assigned before the throw_expression.
- For every variable v, v is definitely assigned after throw_expression.
A throw expression is permitted in only the following syntactic contexts:
- As the second or third operand of a ternary conditional operator
?: - As the second operand of a null coalescing operator
?? - As the body of an expression-bodied lambda or method.