Is it possible to check for variable existence in C#?

Question

I found a similar question, but it was closed and didn't answer this for me.

I have a static class Globals that holds some variables and another Class Stuff that does things. I want Stuff to see if Globals exists and then change some of its variables to the values stored in Globals. I tried

try{
    for (int i = 0; i < Globals.StuffArray.Length; i++)
        StuffArray[i] = Globals.StuffArray[i];
}
catch
{
}

in the constructor for Stuff.

This obviously doesn't work, but the idea was to try to change the variables and to throw an error, that get's ignored, if Globals.StuffArray doesn't exist.

I would still like to know if it's possible to do this, but I'm not solving my problem this way, I added a setter to change the defaults from Globals and that works fine.

update for clarity:

I wanted to make it so that I could leave out Globals and still have Stuff compile.

Update:

In jvascript you can have something like

if (condition1) var x = 0;
if (x) doStuffTo(x);

JavaScript does stuff in the background to make that logical. I wanted to know if C# can do something similar.

To reiterate: I asked because I'm curious if this is possible. Some of the responses seem to have missed the part where I said I'm not going to solve my problem this way, the problem was easily solved by making a property for Globals to change.

At compile time, you should always know whether a class or member exists. What problem are you trying to solve? — SLaks, May 04 '15 at 18:36
You mean "check it for null", not "check if it exists"? Your application wouldn't compile if the variable didn't exist. — mason, May 04 '15 at 18:36
Are you adding these new variables dynamically? I would use a dictionary then you can check if a variable name is in the dictionary instead of an array. — Marko, May 04 '15 at 18:37
I wanted to make it so that if I have globals defined Stuff will use its values and if Globals isn't defined Stuff will use its own default values. — Damien, May 04 '15 at 18:42
No, you can't do that. You will always get a compile-time error if `Globals` does not exist. — John Saunders, May 04 '15 at 18:42
It sounds like this data isn't actually globally applicable data, and as such shouldn't be stored as you're storing it. You should be using a different mechanism entirely to store this data (perhaps a config file that may or may not exist, and a class that can function properly even if the file can't be found, doesn't have sensible values, etc.). — Servy, May 04 '15 at 18:45
If `Stuff` depends on some sort of data, that data should be explicitly declared as a dependence, by using constructor parameters, properties. Using, say, reflection for that is complex and cumbersome IMHO. — rsenna, May 04 '15 at 19:11

Martin Mulder · Accepted Answer · 2015-05-04T18:52:12.060

Use reflection.

With reflection you can:

Load assemblies
See what types are inside an assembly.
See what fields and properties are inside a type.
Read and write their values.
And much more...

During runtime fields and types cannot change in a assembly, so I assume you are refering to an assembly which you do not know at compile time. An assembly which you will load during runtime.

Since I do not know exactly what you need and what you have, my example is an approximation:

var asm = Assembly.LoadFile(@"C:\MyDynamicDll.dll");
var type = asm.GetType("Global");
if (type == null)
    // Do something if Global does not exists.
var fieldInfos = type.GetFields(BindingFlags.Static | BindingFlags.Public); 
foreach(var fieldInfo in fieldInfos)
{
    var value = fieldInfo.GetValue(null);
    // Do something with the value.
}

Be warned: Reflection is pretty slow.

* EDIT *

In your updated question you refer to javascript. Javascript is interpreted during runtime. All types and values are evaluated over and over again, which makes the language a bit slower, but more flexible. C# is interpreted during compilation which makes some things, like types, static which makes it all a bit faster. That is the only reason why script-languages can modify their types during runtime. (Of course there are exception.)

Thanks, that's exactly what I wanted to know. I use reflection to check child class properties from Stuff so that I didn't need to write 10 odd, very similar and long functions. You mentioned Reflection is slow, is it inefficient for me to do it that way? Should I just write out the 10 individual functions. — Damien, May 04 '15 at 18:57
It depends. Suppose a regular call (read and write a property) takes 1us, and reflection 1ms... and you only use it 10 times, then the delay would not be noticable. If you call it a million times, then it would be noticable. — Martin Mulder, May 05 '15 at 00:02

score 0 · Answer 2 · answered May 04 '15 at 18:46

No, you can't do that. You will always get a compile-time error if Globals does not exist.

Also, your try/catch would not have been a best practice. You would have been catching and ignoring more errors than the one you meant to check. Try to keep such blocks as narrow as possible.

Is it possible to check for variable existence in C#?

2 Answers2