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    <p>Update:</p> <blockquote> <p><strong>§ 7.5.7 This access</strong></p> <p>A <em>this-access</em> consists of the reserved word <code>this</code>.</p> <p><em>this-access:</em></p> <pre><code>this </code></pre> <p>A <em>this-access</em> is permitted only in the <em>block</em> of an instance constructor, an instance method, or an instance accessor.</p> </blockquote> <p>This is none of these. The 4.0 compiler looks to be correct. Presumably it isn't happy because this <em>in essence</em> provides access to <code>this</code> at a point when the type isn't initialized. Maybe ;-p</p> <p>Note that I expect that it isn't really the <code>this.someField</code> that causes this - more that the <em>use</em> of a field causes <code>this</code> to be <em>captured</em>, meaning it wants to hoist the <code>this</code> instance onto a compiler-generated class - as though you had written:</p> <pre><code>public MyCtor() : base( new SomeType(this).SomeMethod ) {...} </code></pre> <p>The C# 3.0 compiler spots the above abuse of <code>this</code>.</p> <hr> <p>Reproduced. Investigating. It looks like an issue resolving the implicit <code>this</code> in the constructor chaining.</p> <p>The most likely workaround would be to use a <code>virtual</code> method instead of a delegate, and simply override it in the derived class.</p> <p>One workaround would be to pas the instance in as an argument, so the delegate becomes "obj => obj.whatever...", and use <code>theDelegate(this);</code>. </p> <p>Simpler repro:</p> <pre><code>public class MyBase { public MyBase(Action a) { } } public class MySub : MyBase { private string foo; // with "this.", says invalid use of "this" // without "this.", says instance required public MySub() : base(delegate { this.foo = "abc"; }) { } } </code></pre> <p>I would need to check the spec, but I'm not sure whether <code>this</code> <strong>is</strong> valid in this context... so the 4.0 compiler could be correct.</p>
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    1. USMarc Gravell
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    1. COYour analysis is correct. We discovered this bug late in the C# 3 cycle and postponed fixing it until C# 4. As you correctly note, allowing an anonymous function in this context provides numerous opportunities for accessing "this" before the object has gotten through enough of its initialization sequence to be safe. And as SLaks notes in another posting, we didn't get the codegen "correct" for some of these cases anyway. (I say "correct" in quotes because of course there is no correct codegen defined for an erroneous program.)
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    2. CO@Eric - cheers for the info.
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    3. COthank you for a very thorough answer! I'll have to go through the code and see where this is used and how I can fix it. Might be in many places (this is from N2 open source CMS)
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      1. USRobert Ivanc
 

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