"The C# compiler won't let me do it"

Wednesday, August 11, 2004

Source

In the spirit of language quizes, you can try to find why the following code does not compile:

DictionaryEntry entry1 = new DictionaryEntry();
entry1.Value = 0; // OK

IDictionary dictionary = new Hashtable();
dictionary["dummy"] = "dumb";
foreach (DictionaryEntry entry2 in dictionary)
entry2.Value = 0; // NOT OK : "The left-hand side of an assignment must be a variable, property or indexer"

4 Comments

Is the error just wrong? I mean, you can't assign a new value to "entry2" becuase the enumerated item in a foreach is read-only, so perhaps since your trying to assign a new value to it, it's getting confused.

Roy J. Salisbury @ VsDevCentral - Wednesday, August 11, 2004 6:39:00 PM

DictionaryEntry is a structure and you're foreaching which means the instance is coming from IDictionaryEnumerator.Current therefore assigning to only the local copy. This would be a nasty problem if people forgot about the semantics of value types vs. ref. types, so the C# compiler prevents you from doing this.

Drew Marsh - Wednesday, August 11, 2004 6:56:00 PM

Doh! I forgot all about it being a struct.

Roy J. Salisbury @ VsDevCentral - Wednesday, August 11, 2004 7:06:00 PM

well the error should reflect the problem better.

I was looking at it literally, and not understanding how it could possibly work in one instance and not even 3 lines further down, fail...

So the error should read more like "left-hand assignment is not a ref-type, assignments to any properties or fields will be lost."

Eric Newton - Wednesday, August 11, 2004 7:38:00 PM

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