const parameters in c#

[Joel Holdsworth]

class MyClass
{
public void Foo(const int param)
{
// ... ^^^^^ compile error here
}
}

This type of statment works perfectly well in C++, but a const param seems to confuse the C# compiler a bit. It says "Type Expected". How is it possible pass a constant / read only parameter in C#? Joel Holdsworth Wanna give me a job over the summer? View my online CV and Job Application[^]

[Heath Stewart]

const is not allowed in the parameter list. You should read the C# Language Specification[^]. IIRC, a constant parameter declaration isn't even allowed by the CLI (Common Language Infrastructure).

Microsoft MVP, Visual C# My Articles

[Joel Holdsworth]

Putting /*[in]*/ before each parameter seems to stop them being changable at compile time e.g.

public void foo(/*[in]*/ int foo)
{
// ....
}

- but I get the impression that this is a bit of a cludged way of getting the results. I think I'll just rethink how I do this. Joel Holdsworth Wanna give me a job over the summer? View my online CV and Job Application[^]

[Heath Stewart]

Interesting if true; I've never seen that documented. It would definitely be a compiler feature, though, and have no bearing in the actual code. Keep in mind that an Int32 is a value type and is therefore passed by value. This won't prevent your code from changing it, but if your method implementation does it won't affect the variable that was passed to you (if a variable was indeed passed to your method). Since your method isn't virtual (and hence can't be overridden), just make sure you don't change it. I know that's not a lot of protection, but declaring an argument as constant is really just to avoid future headaches if you forget that you shouldn't change it, IMO.

Microsoft MVP, Visual C# My Articles

[Joel Holdsworth]

Well actually it's not an Int32 - its actually an object which I cooked up myself. Still it seems a bit wierd to not allow const or readonly parameters because, just as you say, they always help me avoid playing around with data which should be left untouched! Joel Holdsworth Wanna give me a job over the summer? View my online CV and Job Application[^]

[leppie]

Joel Holdsworth wrote: Still it seems a bit wierd to not allow const or readonly parameters because, just as you say, they always help me avoid playing around with data which should be left untouched! I agree, alot of errors can be detected at compile time. But that said, comin with generics we should be able to do this:

struct ConstValue<Type T>
{
readonly T value;

ConstValue<T>(T obj)
{
value = obj;
}
static implicit operator ConstValue<T> (T obj)
{
return new ConstValue<T>(cobj);
}
}

Which will serve the same purpose. top secret xacc-ide 0.0.1

[Baris Kurtlutepe]

Joel Holdsworth wrote: Putting /*[in]*/ before each parameter seems to stop them being changable at compile time No it doesn't, or better said: Thank god it doesn't. Thinking of crawling through all comments in the code just to see what other 'features' the compiler might put into the code gives me the creeps.