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< ol class = "chapter" > < li class = "chapter-item expanded " > < a href = "../intro.html" > < strong aria-hidden = "true" > 1.< / strong > Introduction< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/index.html" > < strong aria-hidden = "true" > 2.< / strong > Idioms< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../idioms/coercion-arguments.html" > < strong aria-hidden = "true" > 2.1.< / strong > Use borrowed types for arguments< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/concat-format.html" > < strong aria-hidden = "true" > 2.2.< / strong > Concatenating Strings with format!< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ctor.html" > < strong aria-hidden = "true" > 2.3.< / strong > Constructor< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/default.html" > < strong aria-hidden = "true" > 2.4.< / strong > The Default Trait< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/deref.html" > < strong aria-hidden = "true" > 2.5.< / strong > Collections Are Smart Pointers< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/dtor-finally.html" > < strong aria-hidden = "true" > 2.6.< / strong > Finalisation in Destructors< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/mem-replace.html" > < strong aria-hidden = "true" > 2.7.< / strong > mem::{take(), replace()}< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/on-stack-dyn-dispatch.html" > < strong aria-hidden = "true" > 2.8.< / strong > On-Stack Dynamic Dispatch< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/intro.html" > < strong aria-hidden = "true" > 2.9.< / strong > Foreign function interface (FFI)< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/errors.html" > < strong aria-hidden = "true" > 2.9.1.< / strong > Idiomatic Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/accepting-strings.html" > < strong aria-hidden = "true" > 2.9.2.< / strong > Accepting Strings< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/passing-strings.html" > < strong aria-hidden = "true" > 2.9.3.< / strong > Passing Strings< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/option-iter.html" class = "active" > < strong aria-hidden = "true" > 2.10.< / strong > Iterating over an Option< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/pass-var-to-closure.html" > < strong aria-hidden = "true" > 2.11.< / strong > Pass Variables to Closure< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/priv-extend.html" > < strong aria-hidden = "true" > 2.12.< / strong > Privacy For Extensibility< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/rustdoc-init.html" > < strong aria-hidden = "true" > 2.13.< / strong > Easy doc initialization< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/temporary-mutability.html" > < strong aria-hidden = "true" > 2.14.< / strong > Temporary mutability< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/index.html" > < strong aria-hidden = "true" > 3.< / strong > Design Patterns< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/intro.html" > < strong aria-hidden = "true" > 3.1.< / strong > Behavioural< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/command.html" > < strong aria-hidden = "true" > 3.1.1.< / strong > Command< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/interpreter.html" > < strong aria-hidden = "true" > 3.1.2.< / strong > Interpreter< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/newtype.html" > < strong aria-hidden = "true" > 3.1.3.< / strong > Newtype< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/RAII.html" > < strong aria-hidden = "true" > 3.1.4.< / strong > RAII Guards< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/strategy.html" > < strong aria-hidden = "true" > 3.1.5.< / strong > Strategy< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/visitor.html" > < strong aria-hidden = "true" > 3.1.6.< / strong > Visitor< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded
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< h1 id = "iterating-over-an-option" > < a class = "header" href = "#iterating-over-an-option" > Iterating over an < code > Option< / code > < / a > < / h1 >
< h2 id = "description" > < a class = "header" href = "#description" > Description< / a > < / h2 >
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< p > < code > Option< / code > can be viewed as a container that contains either zero or one
elements. In particular, it implements the < code > IntoIterator< / code > trait, and as such
can be used with generic code that needs such a type.< / p >
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< h2 id = "examples" > < a class = "header" href = "#examples" > Examples< / a > < / h2 >
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< p > Since < code > Option< / code > implements < code > IntoIterator< / code > , it can be used as an argument to
< a href = "https://doc.rust-lang.org/std/iter/trait.Extend.html#tymethod.extend" > < code > .extend()< / code > < / a > :< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" >
< span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let turing = Some(" Turing" );
let mut logicians = vec![" Curry" , " Kleene" , " Markov" ];
logicians.extend(turing);
// equivalent to
if let Some(turing_inner) = turing {
logicians.push(turing_inner);
}
< span class = "boring" > }
< / span > < / code > < / pre > < / pre >
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< p > If you need to tack an < code > Option< / code > to the end of an existing iterator, you can
pass it to < a href = "https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.chain" > < code > .chain()< / code > < / a > :< / p >
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< pre > < pre class = "playground" > < code class = "language-rust edition2018" >
< span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let turing = Some(" Turing" );
let logicians = vec![" Curry" , " Kleene" , " Markov" ];
for logician in logicians.iter().chain(turing.iter()) {
println!(" {} is a logician" , logician);
}
< span class = "boring" > }
< / span > < / code > < / pre > < / pre >
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< p > Note that if the < code > Option< / code > is always < code > Some< / code > , then it is more idiomatic to use
< a href = "https://doc.rust-lang.org/std/iter/fn.once.html" > < code > std::iter::once< / code > < / a > on the
element instead.< / p >
< p > Also, since < code > Option< / code > implements < code > IntoIterator< / code > , it's possible to iterate over
it using a < code > for< / code > loop. This is equivalent to matching it with < code > if let Some(..)< / code > ,
and in most cases you should prefer the latter.< / p >
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< h2 id = "see-also" > < a class = "header" href = "#see-also" > See also< / a > < / h2 >
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< ul >
< li >
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< p > < a href = "https://doc.rust-lang.org/std/iter/fn.once.html" > < code > std::iter::once< / code > < / a > is an
iterator which yields exactly one element. It's a more readable alternative to
< code > Some(foo).into_iter()< / code > .< / p >
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< / li >
< li >
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< p > < a href = "https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.filter_map" > < code > Iterator::filter_map< / code > < / a >
is a version of < a href = "https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.flat_map" > < code > Iterator::flat_map< / code > < / a > ,
specialized to mapping functions which return < code > Option< / code > .< / p >
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< / li >
< li >
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< p > The < a href = "https://crates.io/crates/ref_slice" > < code > ref_slice< / code > < / a > crate provides functions
for converting an < code > Option< / code > to a zero- or one-element slice.< / p >
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< / li >
< li >
< p > < a href = "https://doc.rust-lang.org/std/option/enum.Option.html" > Documentation for < code > Option< T> < / code > < / a > < / p >
< / li >
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