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    <p>Your examples can be divided into two categories: <strong>record expressions</strong> and <strong>record patterns</strong>. While record expressions <em>require to declare all fields</em> and return some expressions, record patterns have <em>optional fields</em> and are for the purpose of pattern matching. <a href="http://msdn.microsoft.com/en-us/library/dd233184.aspx" rel="noreferrer">The MSDN page on Records</a> have two clear sections on them, it may worth a read.</p> <p>In this example,</p> <pre><code>type AnotherPerson = {Id: int; Name: string} type Person = {Id: int; Name: string;} // F# compiler will use second type without any complains or warnings let p = {Id = 42; Name = "Foo";} </code></pre> <p>the behaviour is clear from the rule stated in <a href="http://msdn.microsoft.com/en-us/library/dd233184.aspx" rel="noreferrer">the MSDN page above</a>.</p> <blockquote> <p>The labels of the most recently declared type take precedence over those of the previously declared type</p> </blockquote> <p>In the case of pattern matching, you focus on creating some bindings you need. So you can write </p> <pre><code>type Person = {Id: int; Name: string;} let {Id = id} = p </code></pre> <p>in order to get <code>id</code> binding for later use. Pattern matching on let bindings may look a bit weird, but it's very similar to the way you usually pattern match in function parameters:</p> <pre><code>type Person = {Id: int; Name: string;} let extractName {Name = name} = name </code></pre> <p>I think warnings on your pattern matching examples are justified because the compiler can't guess your intention.</p> <p>Nevertheless, different records with duplicate fields are not recommended. At least you should use qualified names to avoid confusion:</p> <pre><code>type AnotherPerson = {Id: int; Name: string} type Person = {Id: int; Name: string; Age: int} let p = {AnotherPerson.Id = 42; Name = "Foo"} </code></pre>
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    1. POStrange behavior of F# records
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    1. COThanks, @pad. I understand that current behavior for taking last definition is well-documented. But it still seems weird to me. I prefer to get error or warning in this case. And what about my section called "Type inference error with missing field"? Is it seems reasonable to you?
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      1. USSergey Teplyakov
 

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