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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/concat-format.html" class = "active" > < strong aria-hidden = "true" > 2.1.< / strong > Concatenating Strings with format!< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ctor.html" > < strong aria-hidden = "true" > 2.2.< / strong > Constructor< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/default.html" > < strong aria-hidden = "true" > 2.3.< / strong > The Default Trait< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/deref.html" > < strong aria-hidden = "true" > 2.4.< / strong > Collections Are Smart Pointers< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/dtor-finally.html" > < strong aria-hidden = "true" > 2.5.< / strong > Finalisation in Destructors< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/mem-replace.html" > < strong aria-hidden = "true" > 2.6.< / strong > mem::replace(_)< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/on-stack-dyn-dispatch.html" > < strong aria-hidden = "true" > 2.7.< / strong > On-Stack Dynamic Dispatch< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/option-iter.html" > < strong aria-hidden = "true" > 2.8.< / strong > Iterating over an Option< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/pass-var-to-closure.html" > < strong aria-hidden = "true" > 2.9.< / strong > Pass Variables to Closure< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/priv-extend.html" > < strong aria-hidden = "true" > 2.10.< / strong > Privacy For Extensibility< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/rustdoc-init.html" > < strong aria-hidden = "true" > 2.11.< / strong > Easy doc initialization< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/temporary-mutability.html" > < strong aria-hidden = "true" > 2.12.< / 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/builder.html" > < strong aria-hidden = "true" > 3.1.< / strong > Builder< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/compose-structs.html" > < strong aria-hidden = "true" > 3.2.< / strong > Compose Structs< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/fold.html" > < strong aria-hidden = "true" > 3.3.< / strong > Fold< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/newtype.html" > < strong aria-hidden = "true" > 3.4.< / strong > Newtype< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/RAII.html" > < strong aria-hidden = "true" > 3.5.< / strong > RAII Guards< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/small-crates.html" > < strong aria-hidden = "true" > 3.6.< / strong > Prefer Small Crates< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/unsafe-mods.html" > < strong aria-hidden = "true" > 3.7.< / strong > Contain unsafety in small modules< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/visitor.html" > < strong aria-hidden = "true" > 3.8.< / strong > Visitor< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../anti_patterns/index.html" > < strong aria-hidden = "true" > 4.< / strong > Anti-patterns< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../anti_patterns/deny-warnings.html" > < strong aria-hidden = "true" > 4.1.< / strong > #[deny(warnings)]< / a > < / li > < li class = "chapter-item expanded " > < a href = "../anti_patterns/deref.html" > < strong aria-hidden = "true" > 4.2.< / strong > Deref Polymorphism< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../functional/index.html" > < strong aria-hidden = "true" > 5.< / strong > Functional Programming< / a > < / li > < li class = "chapter-item expanded " > < a href = "../additional_resources.html" > < strong aria-hidden = "true" > 6.< / strong > Additional Resources< / a > < / li > < / ol >
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< h1 > < a class = "header" href = "#concatenating-strings-with-format" id = "concatenating-strings-with-format" > Concatenating strings with < code > format!< / code > < / a > < / h1 >
< h2 > < a class = "header" href = "#description" id = "description" > Description< / a > < / h2 >
< p > It is possible to build up strings using the < code > push< / code > and < code > push_str< / code > methods on a
mutable < code > String< / code > , or using its < code > +< / code > operator. However, it is often more
convenient to use < code > format!< / code > , especially where there is a mix of literal and
non-literal strings.< / p >
< h2 > < a class = "header" href = "#example" id = "example" > Example< / a > < / h2 >
< pre > < pre class = "playground" > < code class = "language-rust edition2018" >
< span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > fn say_hello(name: & str) -> String {
// We could construct the result string manually.
// let mut result = " Hello " .to_owned();
// result.push_str(name);
// result.push('!');
// result
// But using format! is better.
format!(" Hello {}!" , name)
}
< span class = "boring" > }
< / span > < / code > < / pre > < / pre >
< h2 > < a class = "header" href = "#advantages" id = "advantages" > Advantages< / a > < / h2 >
< p > Using < code > format!< / code > is usually the most succinct and readable way to combine strings.< / p >
< h2 > < a class = "header" href = "#disadvantages" id = "disadvantages" > Disadvantages< / a > < / h2 >
< p > It is usually not the most efficient way to combine strings - a series of < code > push< / code >
operations on a mutable string is usually the most efficient (especially if the
string has been pre-allocated to the expected size).< / p >
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