Cannot use '=>' syntax for declaring function to throw an exception

[DartBot]

This issue was originally filed by ren...@gmail.com

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What steps will reproduce the problem?

Object thrower(String msg) => throw new UnsupportedOperationException(msg);

What is the expected output? What do you see instead?

Defining the same function with curly braces works, but I don't see why I can't use the short form:

Error: line 1 pos 31: unexpected token 'throw'
Object thrower(String msg) => throw new UnsupportedOperationException(msg);

What version of the product are you using? On what operating system?

Dart SDK version 7904

[DartBot]

This comment was originally written by ladicek@gmail.com

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Note that '=> ...' is a syntactic shortcut for '{ return ... }'. Here, that would mean

Object thrower(String msg) {
  return throw new UnsupportedOperationException(msg);
}

In Dart, not everything is an expression (that returns value), there are also statements. Throw is one of those. I agree that it is inconvenient sometimes, but it makes sense.

[DartBot]

This comment was originally written by re...@gmail.com

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Ok, I understand.

Still I think the following example is rather surprising.

This works:

   void sayHello() => print("Hello");

This doesn't work:
   
   void throwHello() => throw new UnsupportedOperationException("Hello");

Sorry for the short issue-summary, I intended to write a better one but cannot edit it anymore.

[madsager]

Added Area-Language, Triaged labels.
Changed the title to: "Cannot use '=>' syntax for declaring function to throw an exception".

[rakudrama]

Added Duplicate label.
Marked as being merged into #587.