Is VB.NET weakly typed compared to C#

Question

Yesterday I was at an interview where my interviewer (who admittedly didn't claim to be an expert on the subject) stated that "VB.NET is more weakly typed then C#" - (At the same time he couldn't recall an example).

This statement seemed incorrect to me (particularly given that both languages use the same framework libraries for their types) and I advised as such and that perhaps he was confused with the option to turn Option Strict or Option Infer on/off.

At the same time I know that VB.NET has situations where it will do type coercion - leading to occasionally unexpected results (although I also cant recall under what conditions) - (Actually I think I just remembered that it was mainly when performing arithmetic operations with different types - whereas other languages will force you to be explicit (?) ).

So could someone please clarify is VB.NET somehow more weakly typed then C# and if so could you provide examples?

Answer 1

"Weakly typed" and "strongly typed" are effectively meaningless without clarification. The way they are used they usually mean "the type system has features I do not like" or "the type system has features I do like". It sounds like your interviewer does not have a clear idea of what those terms mean, and therefore probably shouldn't be asking questions about them in interviews.

There are a lot of features of type systems that different people say are "strongly typed" vs "weakly typed". For example, some people say that "strongly typed" means "every object knows its own type at runtime". Some people say that "strongly typed" means that the compiler knows the exact type of every variable and expression. Some people say that it means that the compiler has inexact type bounds on every variable and expression. And so on. Every feature of type systems can count as points towards 'strong'.

I say abandon the whole ill-founded notion of "strong" and "weak" typing and talk about what you actually mean.

The differences between the C# and VB type systems are few, particularly since the addition of 'dynamic' to C# 4.0. Both C# and VB use the CLR type system, in which every object knows its own type, and in which illegal type conversions are detected by the runtime (either when the code runs or when it is passed through the verifier) and turned into exceptions. Both have single inheritance for classes and multiple inheritance for interfaces. Both make a distinction between value types and reference types. And so on.

The principle difference between C# and VB type systems is that VB supports optionally dialing down the compile time static type checking, and deferring type checking to runtime, more like a dynamically typed language. This is very handy when interoperating with object models that were designed for dynamic type systems. We added a similar feature to C# 4.0, but in keeping with C# 4.0's historical support of static typing, the feature is based on statically typing certain expressions as "dynamic", which are then resolved by starting up the type analyzer again at runtime and doing the type analysis against the live objects.

More on this subject can be found on my blog:

http://ericlippert.com/2012/10/15/is-c-a-strongly-typed-or-a-weakly-typed-language/