?? operator translation about saltarellecompiler

[erik-kallen]

Yes, the reason is that Script# is wrong:

int? x = 0;
int y = x ?? 1;

should mean y = 0, but the || operator gives y = 1

[erik-kallen]

Thinking about it, Saltarelle is wrong too. x() ?? y() should not evaulate the second function if x() is non-null. Hmm, I wonder how to solve this.

Probably the best way is to use the || operator if the type is statically known to be of types that don't have falsey values (eg normal objects). For types that do have falsey values (string, number, boolean, others?), something else has to be done. Probably something like var y = coalesce(x(), function() { return y(); }, or even an if statement.

[rekna1]

I don't think scriptsharp is wrong, if you write the same code in javascript (with x as a number), it behaves the same way...

ok, it depends whether you want the behavior to be the closed to c# of to javascript, that's another discussion...

[erik-kallen]

Yes, but Saltarelle is designed to follow the C# language specification, not Javascript. This means that whichever code is generated must result in (int?)0 ?? 1 having the value 0. Otherwise I have to write a new specification for a language that is quite similar to C#, but has some semantics taken from Javascript, which is something I do not want to do. See, for example, how I have ensured that variable capture semantics are as they are in C# on the launguage features page: http://www.saltarelle-compiler.com/documentation/supported-c-language-features

[rekna1]

ok, if you put it that way, I agree... so I continue to use coalesce? will it be ok for my case ?

[erik-kallen]

As long as you don't do x() ?? y(), it will be OK. In the next version it will generate an if statement for this.

[erik-kallen]

From 1.3.0 and on the translation will use || if possible (types without falsy values), othwerwise coalesce when the RHS is trivial, or an if statement otherwise.