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copied!<p>This one is a perhaps not-so-obvious special case of "adding/removing interface members", and I figured it deserves its own entry in light of another case which I'm going to post next. So:</p> <h2>Refactoring interface members into a base interface</h2> <p>Kind: breaks at both source and binary levels</p> <p>Languages affected: C#, VB, C++/CLI, F# (for source break; binary one naturally affects any language)</p> <p>API before change:</p> <pre><code>interface IFoo { void Bar(); void Baz(); } </code></pre> <p>API after change:</p> <pre><code>interface IFooBase { void Bar(); } interface IFoo : IFooBase { void Baz(); } </code></pre> <p>Sample client code that is broken by change at source level:</p> <pre><code>class Foo : IFoo { void IFoo.Bar() { ... } void IFoo.Baz() { ... } } </code></pre> <p>Sample client code that is broken by change at binary level;</p> <pre><code>(new Foo()).Bar(); </code></pre> <p>Notes:</p> <p>For source level break, the problem is that C#, VB and C++/CLI all require <em>exact</em> interface name in the declaration of interface member implementation; thus, if the member gets moved to a base interface, the code will no longer compile. </p> <p>Binary break is due to the fact that interface methods are fully qualified in generated IL for explicit implementations, and interface name there must also be exact.</p> <p>Implicit implementation where available (i.e. C# and C++/CLI, but not VB) will work fine on both source and binary level. Method calls do not break either.</p>

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