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C# member variable initialization; best practice?

In C#, is it better to initialise a variable at the time of declaration, or within a constructor?

eg. 

public Foo{
   Bar b = new Bar();
   public Foo() { }
}

OR

public Foo{
    Bar b;
    public Foo() { b = new Bar(); }
}
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  • Better for whatever reasons are important in C# programming. Commented Aug 11, 2010 at 7:45
  • I prefer to go with your latter version. I think it spells out in the most readable way at what time certain pieces of code is executed, and it easily lets me interact with the default behavior by specifying new constructors that may or may not invoke the parameterless constructor. Adding this as a comment as it doesn't attempt to answer which way is better Commented Aug 11, 2010 at 7:47
  • Also: stackoverflow.com/questions/24551/… Commented Aug 11, 2010 at 8:05

4 Answers 4

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Well, "better" depends on the situation.

It's worth knowing that it does end up making a difference in some obscure cases... because the base class constructor gets run after variable initializers, but before the constructor body. That can make a difference in the (nasty) case where a virtual method is called from the base constructor. It's worth avoiding that situation to start with where possible, mind you :)

I think if the initial value never depends on any parameters, it makes sense to initialize it at the point of declaration... but I wouldn't claim to be entirely consistent in applying that myself :)

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2

In a simple class like this it won't make any difference. The advantage of the first is that you could omit the constructor declaration entirely.

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2 Comments

I don't think the example given was a specific implementation.
@dr_tchock: How can you be so sure? Maybe he works in a FooBar factory? ;)
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I simply don't like initializing instance members at the time of declaration, apart from constants. It is just hurting my eyes, especially if the class names are long. Otherwise from a language aspect, it isn't much of a difference.

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5 Comments

Including local variables? I try to initialize local variables at the point of declaration as much as reasonably possible. I find it makes the meaning of the variable clearer.
@Jon Not including local variables:) I think the author was asking for class members, not local variables:) At least this was my impression.
Jon: In all fairness, Petar did specify instance members.
@Gabe I edited my answer to be more clear what I mean. But John posted before that:)
Okay, that makes more sense - thanks for editing.
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It all depends, of course, but I just like to put the initializers where they make the most sense. Sometimes it's good to put them with their member declarations; other times it's good to put them in the constructor.

If I have multiple constructors, though, I prefer to put the initalizers with the declaration, so as to avoid the same initializer code in multiple places -- particularly for readonly fields.

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