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@ -622,9 +622,9 @@ its parts to decide what to do next. In the second phase we may conditionally
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change the value (as in the example above).</p>
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change the value (as in the example above).</p>
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<p>The borrow checker won't allow us to take out <code>name</code> of the enum (because
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<p>The borrow checker won't allow us to take out <code>name</code> of the enum (because
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<em>something</em> must be there. We could of course <code>.clone()</code> name and put the clone
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<em>something</em> must be there. We could of course <code>.clone()</code> name and put the clone
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into our <code>MyEnum::B</code>, but that would be an instance of the [Clone to satisfy
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into our <code>MyEnum::B</code>, but that would be an instance of the <a href="idioms/../anti_patterns/borrow_clone.html">Clone to satisfy
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the borrow checker] antipattern. Anyway, we can avoid the extra allocation by
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the borrow checker</a> antipattern. Anyway, we
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changing <code>e</code> with only a mutable borrow.</p>
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can avoid the extra allocation by changing <code>e</code> with only a mutable borrow.</p>
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<p><code>mem::take</code> lets us swap out the value, replacing it with it's default value,
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<p><code>mem::take</code> lets us swap out the value, replacing it with it's default value,
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and returning the previous value. For <code>String</code>, the default value is an empty
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and returning the previous value. For <code>String</code>, the default value is an empty
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<code>String</code>, which does not need to allocate. As a result, we get the original
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<code>String</code>, which does not need to allocate. As a result, we get the original
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@ -1889,7 +1889,7 @@ is shorter than the lifetime of <code>self</code>.</p>
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using the guard object more ergonomic. Implementing a <code>get</code> method on the guard
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using the guard object more ergonomic. Implementing a <code>get</code> method on the guard
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works just as well.</p>
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works just as well.</p>
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<h2 id="see-also-11"><a class="header" href="#see-also-11">See also</a></h2>
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<h2 id="see-also-11"><a class="header" href="#see-also-11">See also</a></h2>
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<p><a href="patterns/behavioural/../idioms/dtor-finally.html">Finalisation in destructors idiom</a></p>
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<p><a href="patterns/behavioural/../../idioms/dtor-finally.html">Finalisation in destructors idiom</a></p>
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<p>RAII is a common pattern in C++: <a href="http://en.cppreference.com/w/cpp/language/raii">cppreference.com</a>,
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<p>RAII is a common pattern in C++: <a href="http://en.cppreference.com/w/cpp/language/raii">cppreference.com</a>,
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<a href="https://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization">wikipedia</a>.</p>
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<a href="https://en.wikipedia.org/wiki/Resource_Acquisition_Is_Initialization">wikipedia</a>.</p>
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<p><a href="https://doc.rust-lang.org/1.0.0/style/ownership/raii.html">Style guide entry</a>
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<p><a href="https://doc.rust-lang.org/1.0.0/style/ownership/raii.html">Style guide entry</a>
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@ -2141,8 +2141,8 @@ which performs the same duty.</p>
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<h2 id="see-also-13"><a class="header" href="#see-also-13">See also</a></h2>
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<h2 id="see-also-13"><a class="header" href="#see-also-13">See also</a></h2>
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<p>The visitor pattern is a common pattern in most OO languages.</p>
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<p>The visitor pattern is a common pattern in most OO languages.</p>
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<p><a href="https://en.wikipedia.org/wiki/Visitor_pattern">Wikipedia article</a></p>
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<p><a href="https://en.wikipedia.org/wiki/Visitor_pattern">Wikipedia article</a></p>
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<p>The <a href="patterns/behavioural/fold.html">fold</a> pattern is similar to visitor but produces a new version of
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<p>The <a href="patterns/behavioural/../creational/fold.html">fold</a> pattern is similar to visitor but produces
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the visited data structure.</p>
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a new version of the visited data structure.</p>
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<h1 id="creational-patterns"><a class="header" href="#creational-patterns">Creational Patterns</a></h1>
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<h1 id="creational-patterns"><a class="header" href="#creational-patterns">Creational Patterns</a></h1>
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<p>From <a href="https://en.wikipedia.org/wiki/Creational_pattern">Wikipedia</a>:</p>
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<p>From <a href="https://en.wikipedia.org/wiki/Creational_pattern">Wikipedia</a>:</p>
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<blockquote>
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<blockquote>
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@ -2348,10 +2348,10 @@ this fold pattern.</p>
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<p>In other languages, fold is usually used in the sense of Rust's iterators,
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<p>In other languages, fold is usually used in the sense of Rust's iterators,
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rather than this pattern. Some functional languages have powerful constructs for
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rather than this pattern. Some functional languages have powerful constructs for
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performing flexible maps over data structures.</p>
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performing flexible maps over data structures.</p>
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<p>The <a href="patterns/creational/visitor.html">visitor</a> pattern is closely related to fold. They share the
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<p>The <a href="patterns/creational/../behavioural/visitor.html">visitor</a> pattern is closely related to fold.
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concept of walking a data structure performing an operation on each node.
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They share the concept of walking a data structure performing an operation on
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However, the visitor does not create a new data structure nor consume the old
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each node. However, the visitor does not create a new data structure nor consume
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one.</p>
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the old one.</p>
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<h1 id="structural-patterns"><a class="header" href="#structural-patterns">Structural Patterns</a></h1>
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<h1 id="structural-patterns"><a class="header" href="#structural-patterns">Structural Patterns</a></h1>
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<p>From <a href="https://en.wikipedia.org/wiki/Structural_pattern">Wikipedia</a>:</p>
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<p>From <a href="https://en.wikipedia.org/wiki/Structural_pattern">Wikipedia</a>:</p>
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<blockquote>
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<blockquote>
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@ -2738,13 +2738,13 @@ with them:</p>
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into an opaque "object"</p>
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into an opaque "object"</p>
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</li>
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</li>
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<li>
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<li>
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<p><a href="patterns/ffi/../idioms/ffi/errors.html">FFI Error Passing</a> explains error handling with integer
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<p><a href="patterns/ffi/../../idioms/ffi/errors.html">FFI Error Passing</a> explains error handling with integer
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codes and sentinel return values (such as <code>NULL</code> pointers)</p>
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codes and sentinel return values (such as <code>NULL</code> pointers)</p>
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</li>
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</li>
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<li>
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<li>
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<p><a href="patterns/ffi/../idioms/ffi/accepting-strings.html">Accepting Foreign Strings</a> allows accepting
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<p><a href="patterns/ffi/../../idioms/ffi/accepting-strings.html">Accepting Foreign Strings</a> allows accepting
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strings with minimal unsafe code, and is easier to get right than
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strings with minimal unsafe code, and is easier to get right than
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<a href="patterns/ffi/../idioms/ffi/passing-strings.html">Passing Strings to FFI</a></p>
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<a href="patterns/ffi/../../idioms/ffi/passing-strings.html">Passing Strings to FFI</a></p>
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</li>
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</li>
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</ul>
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</ul>
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<p>However, not every API can be done this way.
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<p>However, not every API can be done this way.
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simonsan
3 years ago