Local Variable Type Inference

re: Local Variable Type Inference

rogerj — Mon, 07 May 2007 16:46:39 GMT

You didn't mention that VB 9.0 has local variable type inference with the Dim keyword and Option Infer On|Off.

C# myopia?

--rj

re: Local Variable Type Inference

Arnaud Weil — Wed, 18 Jul 2007 00:39:18 GMT

I see a lot of writing about the fact that var is an inferred type, not a variant. Which should mean it's safe to use, right?

Well, I don't agree and still fear "var" for clean programming. Why? Because we avoid the "variable type" effect of a variant, but it the compiler INFERS the type, then it may infer something different from the developer. For instance:

var d = 1.0;

could declare d as a Decimal instead of a Double.

Now, I have to admin that var is extremely useful for LINQ. I'd just don't rely on it for my business code...

re: Local Variable Type Inference

Ryan Cromwell — Mon, 10 Dec 2007 06:13:08 GMT

How is Arnaud's comment addressed? Resolving to Int versus Long could have some severe consequences.

re: Local Variable Type Inference

EricWhite — Mon, 10 Dec 2007 22:09:36 GMT

One point that I would make regarding local variable type inference: it is for local variables only. For instance, you can't declare the signature of a method using type inference. Regarding the above example:

var d = 1.0;

In that case, type inference uses the rules that the C# compiler uses to determine types of literals, so the type is double, I believe.

In general, after many months of using it, I reserve type inference for two cases:

- where declaring a variable that is an anonymous type (or collection of them). In this case, there is no other option.

- where declaring a parameterized type, and it is a fair amount of typing to explicitly declare the type, yet the typing doesn't add any readability to the code, for example:

var z = new List<string>();