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| <ol class="chapter"><li class="chapter-item affix "><a href="../index.html">Introduction</a></li><li class="chapter-item "><a href="../hello.html"><strong aria-hidden="true">1.</strong> Hello World</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../hello/comment.html"><strong aria-hidden="true">1.1.</strong> Comments</a></li><li class="chapter-item "><a href="../hello/print.html"><strong aria-hidden="true">1.2.</strong> Formatted print</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../hello/print/print_debug.html"><strong aria-hidden="true">1.2.1.</strong> Debug</a></li><li class="chapter-item "><a href="../hello/print/print_display.html"><strong aria-hidden="true">1.2.2.</strong> Display</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../hello/print/print_display/testcase_list.html"><strong aria-hidden="true">1.2.2.1.</strong> Testcase: List</a></li></ol></li><li class="chapter-item "><a href="../hello/print/fmt.html"><strong aria-hidden="true">1.2.3.</strong> Formatting</a></li></ol></li></ol></li><li class="chapter-item "><a href="../primitives.html"><strong aria-hidden="true">2.</strong> Primitives</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../primitives/literals.html"><strong aria-hidden="true">2.1.</strong> Literals and operators</a></li><li class="chapter-item "><a href="../primitives/tuples.html"><strong aria-hidden="true">2.2.</strong> Tuples</a></li><li class="chapter-item "><a href="../primitives/array.html"><strong aria-hidden="true">2.3.</strong> Arrays and Slices</a></li></ol></li><li class="chapter-item "><a href="../custom_types.html"><strong aria-hidden="true">3.</strong> Custom Types</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../custom_types/structs.html"><strong aria-hidden="true">3.1.</strong> Structures</a></li><li class="chapter-item "><a href="../custom_types/enum.html"><strong aria-hidden="true">3.2.</strong> Enums</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../custom_types/enum/enum_use.html"><strong aria-hidden="true">3.2.1.</strong> use</a></li><li class="chapter-item "><a href="../custom_types/enum/c_like.html"><strong aria-hidden="true">3.2.2.</strong> C-like</a></li><li class="chapter-item "><a href="../custom_types/enum/testcase_linked_list.html"><strong aria-hidden="true">3.2.3.</strong> Testcase: linked-list</a></li></ol></li><li class="chapter-item "><a href="../custom_types/constants.html"><strong aria-hidden="true">3.3.</strong> constants</a></li></ol></li><li class="chapter-item "><a href="../variable_bindings.html"><strong aria-hidden="true">4.</strong> Variable Bindings</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../variable_bindings/mut.html"><strong aria-hidden="true">4.1.</strong> Mutability</a></li><li class="chapter-item "><a href="../variable_bindings/scope.html"><strong aria-hidden="true">4.2.</strong> Scope and Shadowing</a></li><li class="chapter-item "><a href="../variable_bindings/declare.html"><strong aria-hidden="true">4.3.</strong> Declare first</a></li><li class="chapter-item "><a href="../variable_bindings/freeze.html"><strong aria-hidden="true">4.4.</strong> Freezing</a></li></ol></li><li class="chapter-item "><a href="../types.html"><strong aria-hidden="true">5.</strong> Types</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../types/cast.html"><strong aria-hidden="true">5.1.</strong> Casting</a></li><li class="chapter-item "><a href="../types/literals.html"><strong aria-hidden="true">5.2.</strong> Literals</a></li><li class="chapter-item "><a href="../types/inference.html"><strong aria-hidden="true">5.3.</strong> Inference</a></li><li class="chapter-item "><a href="../types/alias.html"><strong aria-hidden="true">5.4.</strong> Aliasing</a></li></ol></li><li class="chapter-item "><a href="../conversion.html"><strong aria-hidden="true">6.</strong> Conversion</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../conversion/from_into.html"><strong aria-hidden="true">6.1.</strong> From and Into</a></li><li class="chapter-item "><a href="../conversion/try_from_try_into.html"><strong aria-hidden="true">6.2.</strong> TryFrom and TryInto</a></li><li class="chapter-item "><a href="../conversion/string.html"><strong aria-hidden="true">6.3.</strong> To and from Strings</a></li></ol></li><li class="chapter-item "><a href="../expression.html"><strong aria-hidden="true">7.</strong> Expressions</a></li><li class="chapter-item "><a href="../flow_control.html"><strong aria-hidden="true">8.</strong> Flow of Control</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../flow_control/if_else.html"><strong aria-hidden="true">8.1.</strong> if/else</a></li><li class="chapter-item "><a href="../flow_control/loop.html"><strong aria-hidden="true">8.2.</strong> loop</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../flow_control/loop/nested.html"><strong aria-hidden="true">8.2.1.</strong> Nesting and labels</a></li><li class="chapter-item "><a href="../flow_control/loop/return.html"><strong aria-hidden="true">8.2.2.</strong> Returning from loops</a></li></ol></li><li class="chapter-item "><a href="../flow_control/while.html"><strong aria-hidden="true">8.3.</strong> while</a></li><li class="chapter-item "><a href="../flow_control/for.html"><strong aria-hidden="true">8.4.</strong> for and range</a></li><li class="chapter-item "><a href="../flow_control/match.html"><strong aria-hidden="true">8.5.</strong> match</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../flow_control/match/destructuring.html"><strong aria-hidden="true">8.5.1.</strong> Destructuring</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../flow_control/match/destructuring/destructure_tuple.html"><strong aria-hidden="true">8.5.1.1.</strong> tuples</a></li><li class="chapter-item "><a href="../flow_control/match/destructuring/destructure_enum.html"><strong aria-hidden="true">8.5.1.2.</strong> enums</a></li><li class="chapter-item "><a href="../flow_control/match/destructuring/destructure_pointers.html"><strong aria-hidden="true">8.5.1.3.</strong> pointers/ref</a></li><li class="chapter-item "><a href="../flow_control/match/destructuring/destructure_structures.html"><strong aria-hidden="true">8.5.1.4.</strong> structs</a></li></ol></li><li class="chapter-item "><a href="../flow_control/match/guard.html"><strong aria-hidden="true">8.5.2.</strong> Guards</a></li><li class="chapter-item "><a href="../flow_control/match/binding.html"><strong aria-hidden="true">8.5.3.</strong> Binding</a></li></ol></li><li class="chapter-item "><a href="../flow_control/if_let.html"><strong aria-hidden="true">8.6.</strong> if let</a></li><li class="chapter-item "><a href="../flow_control/while_let.html"><strong aria-hidden="true">8.7.</strong> while let</a></li></ol></li><li class="chapter-item "><a href="../fn.html"><strong aria-hidden="true">9.</strong> Functions</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../fn/methods.html"><strong aria-hidden="true">9.1.</strong> Methods</a></li><li class="chapter-item "><a href="../fn/closures.html"><strong aria-hidden="true">9.2.</strong> Closures</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../fn/closures/capture.html"><strong aria-hidden="true">9.2.1.</strong> Capturing</a></li><li class="chapter-item "><a href="../fn/closures/input_parameters.html"><strong aria-hidden="true">9.2.2.</strong> As input parameters</a></li><li class="chapter-item "><a href="../fn/closures/anonymity.html"><strong aria-hidden="true">9.2.3.</strong> Type anonymity</a></li><li class="chapter-item "><a href="../fn/closures/input_functions.html"><strong aria-hidden="true">9.2.4.</strong> Input functions</a></li><li class="chapter-item "><a href="../fn/closures/output_parameters.html"><strong aria-hidden="true">9.2.5.</strong> As output parameters</a></li><li class="chapter-item "><a href="../fn/closures/closure_examples.html"><strong aria-hidden="true">9.2.6.</strong> Examples in std</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../fn/closures/closure_examples/iter_any.html"><strong aria-hidden="true">9.2.6.1.</strong> Iterator::any</a></li><li class="chapter-item "><a href="../fn/closures/closure_examples/iter_find.html"><strong aria-hidden="true">9.2.6.2.</strong> Searching through iterators</a></li></ol></li></ol></li><li class="chapter-item "><a href="../fn/hof.html"><strong aria-hidden="true">9.3.</strong> Higher Order Functions</a></li><li class="chapter-item "><a href="../fn/diverging.html"><strong aria-hidden="true">9.4.</strong> Diverging functions</a></li></ol></li><li class="chapter-item "><a href="../mod.html"><strong aria-hidden="true">10.</strong> Modules</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../mod/visibility.html"><strong aria-hidden="true">10.1.</strong> Visibility</a></li><li class="chapter-item "><a href="../mod/struct_visibility.html"><strong aria-hidden="true">10.2.</strong> Struct visibility</a></li><li class="chapter-item "><a href="../mod/use.html"><strong aria-hidden="true">10.3.</strong> The use declaration</a></li><li class="chapter-item "><a href="../mod/super.html"><strong aria-hidden="true">10.4.</strong> super and self</a></li><li class="chapter-item "><a href="../mod/split.html"><strong aria-hidden="true">10.5.</strong> File hierarchy</a></li></ol></li><li class="chapter-item "><a href="../crates.html"><strong aria-hidden="true">11.</strong> Crates</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../crates/lib.html"><strong aria-hidden="true">11.1.</strong> Creating a Library</a></li><li class="chapter-item "><a href="../crates/using_lib.html"><strong aria-hidden="true">11.2.</strong> Using a Library</a></li></ol></li><li class="chapter-item "><a href="../cargo.html"><strong aria-hidden="true">12.</strong> Cargo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../cargo/deps.html"><strong aria-hidden="true">12.1.</strong> Dependencies</a></li><li class="chapter-item "><a href="../cargo/conventions.html"><strong aria-hidden="true">12.2.</strong> Conventions</a></li><li class="chapter-item "><a href="../cargo/test.html"><strong aria-hidden="true">12.3.</strong> Tests</a></li><li class="chapter-item "><a href="../cargo/build_scripts.html"><strong aria-hidden="true">12.4.</strong> Build Scripts</a></li></ol></li><li class="chapter-item "><a href="../attribute.html"><strong aria-hidden="true">13.</strong> Attributes</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../attribute/unused.html"><strong aria-hidden="true">13.1.</strong> dead_code</a></li><li class="chapter-item "><a href="../attribute/crate.html"><strong aria-hidden="true">13.2.</strong> Crates</a></li><li class="chapter-item "><a href="../attribute/cfg.html"><strong aria-hidden="true">13.3.</strong> cfg</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../attribute/cfg/custom.html"><strong aria-hidden="true">13.3.1.</strong> Custom</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../generics.html"><strong aria-hidden="true">14.</strong> Generics</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../generics/gen_fn.html"><strong aria-hidden="true">14.1.</strong> Functions</a></li><li class="chapter-item "><a href="../generics/impl.html"><strong aria-hidden="true">14.2.</strong> Implementation</a></li><li class="chapter-item "><a href="../generics/gen_trait.html"><strong aria-hidden="true">14.3.</strong> Traits</a></li><li class="chapter-item "><a href="../generics/bounds.html"><strong aria-hidden="true">14.4.</strong> Bounds</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../generics/bounds/testcase_empty.html"><strong aria-hidden="true">14.4.1.</strong> Testcase: empty bounds</a></li></ol></li><li class="chapter-item "><a href="../generics/multi_bounds.html"><strong aria-hidden="true">14.5.</strong> Multiple bounds</a></li><li class="chapter-item "><a href="../generics/where.html"><strong aria-hidden="true">14.6.</strong> Where clauses</a></li><li class="chapter-item "><a href="../generics/new_types.html"><strong aria-hidden="true">14.7.</strong> New Type Idiom</a></li><li class="chapter-item "><a href="../generics/assoc_items.html"><strong aria-hidden="true">14.8.</strong> Associated items</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../generics/assoc_items/the_problem.html"><strong aria-hidden="true">14.8.1.</strong> The Problem</a></li><li class="chapter-item "><a href="../generics/assoc_items/types.html"><strong aria-hidden="true">14.8.2.</strong> Associated types</a></li></ol></li><li class="chapter-item expanded "><a href="../generics/phantom.html" class="active"><strong aria-hidden="true">14.9.</strong> Phantom type parameters</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../generics/phantom/testcase_units.html"><strong aria-hidden="true">14.9.1.</strong> Testcase: unit clarification</a></li></ol></li></ol></li><li class="chapter-item "><a href="../scope.html"><strong aria-hidden="true">15.</strong> Scoping rules</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../scope/raii.html"><strong aria-hidden="true">15.1.</strong> RAII</a></li><li class="chapter-item "><a href="../scope/move.html"><strong aria-hidden="true">15.2.</strong> Ownership and moves</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../scope/move/mut.html"><strong aria-hidden="true">15.2.1.</strong> Mutability</a></li><li class="chapter-item "><a href="../scope/move/partial_move.html"><strong aria-hidden="true">15.2.2.</strong> Partial moves</a></li></ol></li><li class="chapter-item "><a href="../scope/borrow.html"><strong aria-hidden="true">15.3.</strong> Borrowing</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../scope/borrow/mut.html"><strong aria-hidden="true">15.3.1.</strong> Mutability</a></li><li class="chapter-item "><a href="../scope/borrow/alias.html"><strong aria-hidden="true">15.3.2.</strong> Aliasing</a></li><li class="chapter-item "><a href="../scope/borrow/ref.html"><strong aria-hidden="true">15.3.3.</strong> The ref pattern</a></li></ol></li><li class="chapter-item "><a href="../scope/lifetime.html"><strong aria-hidden="true">15.4.</strong> Lifetimes</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../scope/lifetime/explicit.html"><strong aria-hidden="true">15.4.1.</strong> Explicit annotation</a></li><li class="chapter-item "><a href="../scope/lifetime/fn.html"><strong aria-hidden="true">15.4.2.</strong> Functions</a></li><li class="chapter-item "><a href="../scope/lifetime/methods.html"><strong aria-hidden="true">15.4.3.</strong> Methods</a></li><li class="chapter-item "><a href="../scope/lifetime/struct.html"><strong aria-hidden="true">15.4.4.</strong> Structs</a></li><li class="chapter-item "><a href="../scope/lifetime/trait.html"><strong aria-hidden="true">15.4.5.</strong> Traits</a></li><li class="chapter-item "><a href="../scope/lifetime/lifetime_bounds.html"><strong aria-hidden="true">15.4.6.</strong> Bounds</a></li><li class="chapter-item "><a href="../scope/lifetime/lifetime_coercion.html"><strong aria-hidden="true">15.4.7.</strong> Coercion</a></li><li class="chapter-item "><a href="../scope/lifetime/static_lifetime.html"><strong aria-hidden="true">15.4.8.</strong> Static</a></li><li class="chapter-item "><a href="../scope/lifetime/elision.html"><strong aria-hidden="true">15.4.9.</strong> Elision</a></li></ol></li></ol></li><li class="chapter-item "><a href="../trait.html"><strong aria-hidden="true">16.</strong> Traits</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../trait/derive.html"><strong aria-hidden="true">16.1.</strong> Derive</a></li><li class="chapter-item "><a href="../trait/dyn.html"><strong aria-hidden="true">16.2.</strong> Returning Traits with dyn</a></li><li class="chapter-item "><a href="../trait/ops.html"><strong aria-hidden="true">16.3.</strong> Operator Overloading</a></li><li class="chapter-item "><a href="../trait/drop.html"><strong aria-hidden="true">16.4.</strong> Drop</a></li><li class="chapter-item "><a href="../trait/iter.html"><strong aria-hidden="true">16.5.</strong> Iterators</a></li><li class="chapter-item "><a href="../trait/impl_trait.html"><strong aria-hidden="true">16.6.</strong> impl Trait</a></li><li class="chapter-item "><a href="../trait/clone.html"><strong aria-hidden="true">16.7.</strong> Clone</a></li><li class="chapter-item "><a href="../trait/supertraits.html"><strong aria-hidden="true">16.8.</strong> Supertraits</a></li><li class="chapter-item "><a href="../trait/disambiguating.html"><strong aria-hidden="true">16.9.</strong> Disambiguating overlapping traits</a></li></ol></li><li class="chapter-item "><a href="../macros.html"><strong aria-hidden="true">17.</strong> macro_rules!</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../macros/syntax.html"><strong aria-hidden="true">17.1.</strong> Syntax</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../macros/designators.html"><strong aria-hidden="true">17.1.1.</strong> Designators</a></li><li class="chapter-item "><a href="../macros/overload.html"><strong aria-hidden="true">17.1.2.</strong> Overload</a></li><li class="chapter-item "><a href="../macros/repeat.html"><strong aria-hidden="true">17.1.3.</strong> Repeat</a></li></ol></li><li class="chapter-item "><a href="../macros/dry.html"><strong aria-hidden="true">17.2.</strong> DRY (Don't Repeat Yourself)</a></li><li class="chapter-item "><a href="../macros/dsl.html"><strong aria-hidden="true">17.3.</strong> DSL (Domain Specific Languages)</a></li><li class="chapter-item "><a href="../macros/variadics.html"><strong aria-hidden="true">17.4.</strong> Variadics</a></li></ol></li><li class="chapter-item "><a href="../error.html"><strong aria-hidden="true">18.</strong> Error handling</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../error/panic.html"><strong aria-hidden="true">18.1.</strong> panic</a></li><li class="chapter-item "><a href="../error/option_unwrap.html"><strong aria-hidden="true">18.2.</strong> Option & unwrap</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../error/option_unwrap/question_mark.html"><strong aria-hidden="true">18.2.1.</strong> Unpacking options with ?</a></li><li class="chapter-item "><a href="../error/option_unwrap/map.html"><strong aria-hidden="true">18.2.2.</strong> Combinators: map</a></li><li class="chapter-item "><a href="../error/option_unwrap/and_then.html"><strong aria-hidden="true">18.2.3.</strong> Combinators: and_then</a></li></ol></li><li class="chapter-item "><a href="../error/result.html"><strong aria-hidden="true">18.3.</strong> Result</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../error/result/result_map.html"><strong aria-hidden="true">18.3.1.</strong> map for Result</a></li><li class="chapter-item "><a href="../error/result/result_alias.html"><strong aria-hidden="true">18.3.2.</strong> aliases for Result</a></li><li class="chapter-item "><a href="../error/result/early_returns.html"><strong aria-hidden="true">18.3.3.</strong> Early returns</a></li><li class="chapter-item "><a href="../error/result/enter_question_mark.html"><strong aria-hidden="true">18.3.4.</strong> Introducing ?</a></li></ol></li><li class="chapter-item "><a href="../error/multiple_error_types.html"><strong aria-hidden="true">18.4.</strong> Multiple error types</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../error/multiple_error_types/option_result.html"><strong aria-hidden="true">18.4.1.</strong> Pulling Results out of Options</a></li><li class="chapter-item "><a href="../error/multiple_error_types/define_error_type.html"><strong aria-hidden="true">18.4.2.</strong> Defining an error type</a></li><li class="chapter-item "><a href="../error/multiple_error_types/boxing_errors.html"><strong aria-hidden="true">18.4.3.</strong> Boxing errors</a></li><li class="chapter-item "><a href="../error/multiple_error_types/reenter_question_mark.html"><strong aria-hidden="true">18.4.4.</strong> Other uses of ?</a></li><li class="chapter-item "><a href="../error/multiple_error_types/wrap_error.html"><strong aria-hidden="true">18.4.5.</strong> Wrapping errors</a></li></ol></li><li class="chapter-item "><a href="../error/iter_result.html"><strong aria-hidden="true">18.5.</strong> Iterating over Results</a></li></ol></li><li class="chapter-item "><a href="../std.html"><strong aria-hidden="true">19.</strong> Std library types</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std/box.html"><strong aria-hidden="true">19.1.</strong> Box, stack and heap</a></li><li class="chapter-item "><a href="../std/vec.html"><strong aria-hidden="true">19.2.</strong> Vectors</a></li><li class="chapter-item "><a href="../std/str.html"><strong aria-hidden="true">19.3.</strong> Strings</a></li><li class="chapter-item "><a href="../std/option.html"><strong aria-hidden="true">19.4.</strong> Option</a></li><li class="chapter-item "><a href="../std/result.html"><strong aria-hidden="true">19.5.</strong> Result</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std/result/question_mark.html"><strong aria-hidden="true">19.5.1.</strong> ?</a></li></ol></li><li class="chapter-item "><a href="../std/panic.html"><strong aria-hidden="true">19.6.</strong> panic!</a></li><li class="chapter-item "><a href="../std/hash.html"><strong aria-hidden="true">19.7.</strong> HashMap</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std/hash/alt_key_types.html"><strong aria-hidden="true">19.7.1.</strong> Alternate/custom key types</a></li><li class="chapter-item "><a href="../std/hash/hashset.html"><strong aria-hidden="true">19.7.2.</strong> HashSet</a></li></ol></li><li class="chapter-item "><a href="../std/rc.html"><strong aria-hidden="true">19.8.</strong> Rc</a></li><li class="chapter-item "><a href="../std/arc.html"><strong aria-hidden="true">19.9.</strong> Arc</a></li></ol></li><li class="chapter-item "><a href="../std_misc.html"><strong aria-hidden="true">20.</strong> Std misc</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std_misc/threads.html"><strong aria-hidden="true">20.1.</strong> Threads</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std_misc/threads/testcase_mapreduce.html"><strong aria-hidden="true">20.1.1.</strong> Testcase: map-reduce</a></li></ol></li><li class="chapter-item "><a href="../std_misc/channels.html"><strong aria-hidden="true">20.2.</strong> Channels</a></li><li class="chapter-item "><a href="../std_misc/path.html"><strong aria-hidden="true">20.3.</strong> Path</a></li><li class="chapter-item "><a href="../std_misc/file.html"><strong aria-hidden="true">20.4.</strong> File I/O</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std_misc/file/open.html"><strong aria-hidden="true">20.4.1.</strong> open</a></li><li class="chapter-item "><a href="../std_misc/file/create.html"><strong aria-hidden="true">20.4.2.</strong> create</a></li><li class="chapter-item "><a href="../std_misc/file/read_lines.html"><strong aria-hidden="true">20.4.3.</strong> read lines</a></li></ol></li><li class="chapter-item "><a href="../std_misc/process.html"><strong aria-hidden="true">20.5.</strong> Child processes</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std_misc/process/pipe.html"><strong aria-hidden="true">20.5.1.</strong> Pipes</a></li><li class="chapter-item "><a href="../std_misc/process/wait.html"><strong aria-hidden="true">20.5.2.</strong> Wait</a></li></ol></li><li class="chapter-item "><a href="../std_misc/fs.html"><strong aria-hidden="true">20.6.</strong> Filesystem Operations</a></li><li class="chapter-item "><a href="../std_misc/arg.html"><strong aria-hidden="true">20.7.</strong> Program arguments</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../std_misc/arg/matching.html"><strong aria-hidden="true">20.7.1.</strong> Argument parsing</a></li></ol></li><li class="chapter-item "><a href="../std_misc/ffi.html"><strong aria-hidden="true">20.8.</strong> Foreign Function Interface</a></li></ol></li><li class="chapter-item "><a href="../testing.html"><strong aria-hidden="true">21.</strong> Testing</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../testing/unit_testing.html"><strong aria-hidden="true">21.1.</strong> Unit testing</a></li><li class="chapter-item "><a href="../testing/doc_testing.html"><strong aria-hidden="true">21.2.</strong> Documentation testing</a></li><li class="chapter-item "><a href="../testing/integration_testing.html"><strong aria-hidden="true">21.3.</strong> Integration testing</a></li><li class="chapter-item "><a href="../testing/dev_dependencies.html"><strong aria-hidden="true">21.4.</strong> Dev-dependencies</a></li></ol></li><li class="chapter-item "><a href="../unsafe.html"><strong aria-hidden="true">22.</strong> Unsafe Operations</a></li><li class="chapter-item "><a href="../compatibility.html"><strong aria-hidden="true">23.</strong> Compatibility</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../compatibility/raw_identifiers.html"><strong aria-hidden="true">23.1.</strong> Raw identifiers</a></li></ol></li><li class="chapter-item "><a href="../meta.html"><strong aria-hidden="true">24.</strong> Meta</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../meta/doc.html"><strong aria-hidden="true">24.1.</strong> Documentation</a></li><li class="chapter-item "><a href="../meta/playpen.html"><strong aria-hidden="true">24.2.</strong> Playpen</a></li></ol></li></ol> |
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| <h1 id="phantom-type-parameters"><a class="header" href="#phantom-type-parameters">Phantom type parameters</a></h1> |
| <p>A phantom type parameter is one that doesn't show up at runtime, |
| but is checked statically (and only) at compile time.</p> |
| <p>Data types can use extra generic type parameters to act as markers |
| or to perform type checking at compile time. These extra parameters |
| hold no storage values, and have no runtime behavior.</p> |
| <p>In the following example, we combine <a href="https://doc.rust-lang.org/std/marker/struct.PhantomData.html">std::marker::PhantomData</a> |
| with the phantom type parameter concept to create tuples containing |
| different data types.</p> |
| <pre><pre class="playground"><code class="language-rust editable">use std::marker::PhantomData; |
| |
| // A phantom tuple struct which is generic over `A` with hidden parameter `B`. |
| #[derive(PartialEq)] // Allow equality test for this type. |
| struct PhantomTuple<A, B>(A,PhantomData<B>); |
| |
| // A phantom type struct which is generic over `A` with hidden parameter `B`. |
| #[derive(PartialEq)] // Allow equality test for this type. |
| struct PhantomStruct<A, B> { first: A, phantom: PhantomData<B> } |
| |
| // Note: Storage is allocated for generic type `A`, but not for `B`. |
| // Therefore, `B` cannot be used in computations. |
| |
| fn main() { |
| // Here, `f32` and `f64` are the hidden parameters. |
| // PhantomTuple type specified as `<char, f32>`. |
| let _tuple1: PhantomTuple<char, f32> = PhantomTuple('Q', PhantomData); |
| // PhantomTuple type specified as `<char, f64>`. |
| let _tuple2: PhantomTuple<char, f64> = PhantomTuple('Q', PhantomData); |
| |
| // Type specified as `<char, f32>`. |
| let _struct1: PhantomStruct<char, f32> = PhantomStruct { |
| first: 'Q', |
| phantom: PhantomData, |
| }; |
| // Type specified as `<char, f64>`. |
| let _struct2: PhantomStruct<char, f64> = PhantomStruct { |
| first: 'Q', |
| phantom: PhantomData, |
| }; |
| |
| // Compile-time Error! Type mismatch so these cannot be compared: |
| //println!("_tuple1 == _tuple2 yields: {}", |
| // _tuple1 == _tuple2); |
| |
| // Compile-time Error! Type mismatch so these cannot be compared: |
| //println!("_struct1 == _struct2 yields: {}", |
| // _struct1 == _struct2); |
| } |
| </code></pre></pre> |
| <h3 id="see-also"><a class="header" href="#see-also">See also:</a></h3> |
| <p><a href="../trait/derive.html">Derive</a>, <a href="../custom_types/structs.html">struct</a>, and <a href="../custom_types/structs.html">TupleStructs</a></p> |
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