In the body of a class, why does field initialization work but method calls don't?

Question

In C#, why doesn't field initializer syntax not throw compilation errors, however, method calls do? For example,

class SomeOtherClass {
    void SomeMethod() { }
}

class SomeClass {

    SomeOtherClass someOtherObject = new SomeOtherClass();
    someOtherObject.SomeMethod();
}

Why does the someOtherObject initialization, which essentially is a constructor call work? My understanding is that a constructor is also a method. However the second line, where there is a method call, does not work. Is this a language design choice?

A class is just a skeleton, it can not on its own perform operations/action. Assume suppose it is allowed then simply you don't have control over the class behavior i.e. you don't have a way to do a set of operations as and when required in a controlled manner. But it is perfectly fine to invoke methods/actions from within constructor so that class instantiation itself can do some basic stuff for you. + OOPS (object orientation)!! Hope you get it.. — Siva Gopal, Nov 21 '15 at 16:47
+ Check [this SO](http://stackoverflow.com/questions/14439231/a-field-initializer-cannot-reference-the-nonstatic-field-method-or-property) — Siva Gopal, Nov 21 '15 at 16:59

score 2 · Accepted Answer · answered Nov 21 '15 at 17:14

SomeOtherClass someOtherObject = new SomeOtherClass();

is syntactic sugar for this anyway:

SomeOtherClass someOtherObject;

public SomeClass() {
    someOtherObject = new SomeOtherClass()
}

So nothing is executed outside of the constructor. The compiler will create an empty constructor if it doesn't exist and initialize someOtherObject.

score 0 · Answer 2 · answered Nov 21 '15 at 16:41

0

A Class contains attributes and methods declarations and definitions only. Attributes can be initialized right there as you're doing

SomeOtherClass someOtherObject = new SomeOtherClass();

and in the constructors.

Doing

someOtherObject.SomeMethod();

is neither declaration/definition nor initialization. Which is not allowed.

answered Nov 21 '15 at 16:41

Muhammad Rehan Qadri

411
3
14

**Why** is it not allowed? – Saikat Das Nov 21 '15 at 16:45
When will the compiler run this line? This is neither in Main nor you can invoke it anywhere. – Muhammad Rehan Qadri Nov 21 '15 at 16:46
Right. So, applying the same logic, shouldn't the constructor call also not be allowed. The constructor call is also a method call. – Saikat Das Nov 21 '15 at 16:48
As mentioned, initialization is allowed because the compiler needs to initialize every member (attributes) so it'll call its constructors to initalize it when an object of class is created. But there is no way someOtherObject.SomeMethod(); will be called. – Muhammad Rehan Qadri Nov 21 '15 at 16:55

In the body of a class, why does field initialization work but method calls don't?

2 Answers2