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    <p>Tejas's answer is correct. To more specifically address some of your points:</p> <blockquote> <p>Why does the following code not result in compile error? </p> </blockquote> <p>The question is not answerable; it does not produce an error because it is legal code, but that's a tautology. </p> <p>If your question is actually "which section of the C# specification makes this legal?", then that's an answerable question. The section on lifted equality operators makes it legal.</p> <blockquote> <p>It's comparing a reference type to primitive type. </p> </blockquote> <p>It is not. First off, avoid the term "primitive type"; the specification does not clearly define it and it is not a useful concept in C#. You meant to say I think that it is comparing a value of reference type to a value of value type.</p> <p>Second, that's not correct either. The null literal is not of reference type or value type; it is of no type. It is <em>convertible</em> to any nullable value type or any reference type, but it is of no type just by itself.</p> <p>In this case the null literal is converted to the nullable bool type.</p> <blockquote> <p>Both null and false have to be interpreted into something for the compiler to do comparison. </p> </blockquote> <p>Correct. They are interpreted as nullable bools.</p> <blockquote> <p>is the parser simply scanning for such pattern and replace it with false?</p> </blockquote> <p>No, but that's an excellent guess. The compiler <em>would</em> constant-fold, say, <code>true == false</code> down to <code>false</code>, but it does not do folding optimizations that involve nullable value types. The language could be redesigned to support constant folding on operations with nullable value type operands; had nullable value types counterfactually been in version one, the proposed feature likely would have been supported.</p>
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    1. POWhy null == false does not result in compile error in c#?
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    1. USVishal Suthar
    1. USEric Lippert
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    1. COThanks for setting the records straight.
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      1. USweilin8
    2. COWas the comparison also valid in C# before nullable types?
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      1. USAnders Forsgren
    3. CO@AndersForsgren: Was *what* comparison valid, in which version of C#?
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