C# Blooper №3: No warnings about fields having already been initialized.

Before reading any further, please read the disclaimer.

When you declare a member variable and you pre-initialize it at the same time, and then you try to re-initialize it within the constructor without ever making use of its original pre-initialized value, you receive no warning about the field having already been initialized.

namespace Test3 
{  
    public class Test 
    {  
        public readonly string m = "m"; 
        public string n = "n"; 
        private string o = "o"; 
        protected readonly string p = "p"; 
        protected string q = "p"; 
        private string r = "r"; 

        Test() 
        {  
            m = "m2"; //Blooper: no warning about field having already been initialized. 
            n = "n2"; //Blooper: no warning about field having already been initialized. 
            o = "o2"; //Blooper: no warning about field having already been initialized. 
            p = "p2"; //Blooper: no warning about field having already been initialized. 
            q = "q2"; //Blooper: no warning about field having already been initialized. 
            r = "r2"; //Blooper: no warning about field having already been initialized. 
            o.ToLower(); //to prevent Warning CS0414: The field is assigned but its value is never used. 
            r.ToLower(); //to prevent Warning CS0414: The field is assigned but its value is never used. 
        }  
    } 
}  

This means that you may accidentally invoke complex initialization logic twice, unnecessarily wasting memory and clock cycles, and it may also lead to logic errors, if by any chance that initialization logic has side effects which are only meant to occur once. It may also confuse someone reading your code, (or even yourself looking at your code months later,) trying to figure out what's the purpose behind the seemingly repeated initialization, before the realization sinks in that it is simply redundant. Furthermore, if the re-initialization happens to differ from the pre-initialization, a good question arises, asking which one of the two was meant to be the correct one.

It is a pity, because the compiler could warn the programmer against this pitfall.

Also see related post: C# Blooper №2: No warnings about accessing uninitialized members.

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