For example,
static void Main()
{
var someVar = 3;
Console.Write(GetVariableName(someVar));
}
The output of this program should be:
someVar
How can I achieve that using reflection?
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1@helen my question is pretty simple, as opposed to the scatter of a question he came up with, which still I think rather different.Eran Betzalel– Eran Betzalel2010-04-02 10:38:39 +00:00Commented Apr 2, 2010 at 10:38
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What could possibly be the reasoning behind this?Dested– Dested2010-04-02 13:11:54 +00:00Commented Apr 2, 2010 at 13:11
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2 Answers
It is not possible to do this with reflection, because variables won't have a name once compiled to IL. However, you can use expression trees and promote the variable to a closure:
static string GetVariableName<T>(Expression<Func<T>> expr)
{
var body = (MemberExpression)expr.Body;
return body.Member.Name;
}
You can use this method as follows:
static void Main()
{
var someVar = 3;
Console.Write(GetVariableName(() => someVar));
}
Note that this is pretty slow, so don't use it in performance critical paths of your application. Every time this code runs, several objects are created (which causes GC pressure) and under the cover many non-inlinable methods are called and some heavy reflection is used.
For a more complete example, see here.
UPDATE
With C# 6.0, the nameof keyword is added to the language, which allows us to do the following:
static void Main()
{
var someVar = 3;
Console.Write(nameof(someVar));
}
This is obviously much more convenient and has the same cost has defining the string as constant string literal.
6 Comments
Alexandra Rusina
I am not sure that it's really bad in terms of performance. What might cause performance problems is compiling expression trees, but you don't do it here.
Steven
Look for your self where the
GetVariableName(() => someVar) gets compiled to using Reflector. Every time this code runs, several objects are created and under the cover many non-inlinable methods are called and some heavy reflection is used. Using expression trees isn't free.Alexandra Rusina
Yes, you are right. It does have performance cost. But it "relatively" small comparing to compiling expression trees.
Steven
I get your point. You are talking about compiling expression trees at runtime, by calling their
.Compile() method. I agree that this is even more costlier.
Bart
+1 for 'even more costlier' :)
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You can't, using reflection. GetVariableName is passed the number 3, not a variable. You could do this via code inspect of the IL, but that's probably in the too-hard basket.
