(0 == variable) or (null == obj): An outdated practice in C#?

Question

Exact duplicate:

Why does one often see “null != variable” instead of “variable != null” in C#?

I have seen senior developers using syntaxes mentioned in the title.

Is there a need for specifying a constant first in .NET? (as opposed to in C/C++ world)

Answer 1

No, there's no need for this, because the problem it tries to avoid - namely the typo of:

if (variable = 0)

wouldn't compile in C# anyway. The conditions in if statements have to be Boolean. There's still a risk of making one of these mistakes:

if (something = true)
if (something = false)

if something is a Boolean variable, but the better way to fix this is to avoid the constant:

if (something)
if (!something)

If you have developers bringing over idioms like this from other languages without thinking about whether they're appropriate in C#, you should keep an eye for them doing more of the same. If you try to write C# as if it's C++ (or any other language, pretty much - with the possible exception of VB.NET) you'll end up writing non-idiomatic C# code.

EDIT: As cletus noted, there is another potential area for concern:

bool a = false, b = true; 
if (a = b) { } // No warnings

So the error can still occur - but then we're outside the realm of comparing with a constant anyway :) I'd say this crops up incredibly rarely, and isn't worth too much time spent worrying about it.

Answer 2

I suspect this is a leftover habit. In C:

 if (0 = variable)

will throw a compiler error whereas

 if (variable = 0)

will not.

Answer 3

There is no need for this syntax in the modern world. It's a habit that many of us got into when our C compiler wouldn't warn us that we were about to launch the missiles.

if(status = RED_ALERT)
{
    launchMissiles();
}

Answer 4

It's not needed for C#. But It's still a good idea.

Programming is all about habit and you never know when you'll find yourself writing some javascript or updating an old program you thought was long gone.