Why can't I initialize readonly variables in a initializer?

Question

Why can't I initialize readonly variables in a initializer? The following doesn't work as it should:

class Foo {     public readonly int bar; }  new Foo { bar=0; }; // does not work 

Is this due to some technical limits of the CLR?

EDIT

I know that new Foo { bar=0; } is the same as new Foo().bar=0;, but is "readonly" enforced by the CLR, or is it just a compiler limitation?

Answer 1

The initializer is just syntactic sugar. When you write:

new Foo { bar=0; }; 

(Which, by the way, is a syntax error and should be this...)

new Foo { bar=0 } 

what's actually happening is:

var x = new Foo(); x.bar = 0; 

Since the property is read-only, that second statement is invalid.

Edit: Based on your edit, the question is a little unclear. A readonly property is, by design, not settable. It's built at object construction. This is enforced by both the compiler and the runtime. (Admittedly, I haven't tested the latter, since it would take some trickery to get around the former.)

Keep in mind that there are two stages of "compilation." It's enforced when compiling the C# code into IL code, and it's enforced when compiling the IL code into machine code.

It's not a technical limit of the CLR, and it's working exactly as it should, given the explicit readonly declaration. After the object is constructed, you can't set a readonly property.