Added AsXxxCase wrappers

src/kebab.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{lowercase, transform};
 
 /// This trait defines a kebab case conversion.
@@ -19,7 +21,25 @@ pub trait ToKebabCase: ToOwned {
 
 impl ToKebabCase for str {
     fn to_kebab_case(&self) -> Self::Owned {
-        transform(self, lowercase, |s| s.push('-'))
+        AsKebabCase(self).to_string()
+    }
+}
+
+/// This wrapper performs a kebab case conversion in [`fmt::Display`].
+///
+/// ## Example:
+///
+/// ```
+/// use heck::AsKebabCase;
+///
+/// let sentence = "We are going to inherit the earth.";
+/// assert_eq!(format!("{}", AsKebabCase(sentence)), "we-are-going-to-inherit-the-earth");
+/// ```
+pub struct AsKebabCase<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for AsKebabCase<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        transform(self.0.as_ref(), lowercase, |f| write!(f, "-"), f)
     }
 }
 

src/lib.rs

@@ -48,20 +48,31 @@ mod snake;
 mod title;
 mod upper_camel;
 
-pub use kebab::ToKebabCase;
-pub use lower_camel::ToLowerCamelCase;
-pub use shouty_kebab::ToShoutyKebabCase;
-pub use shouty_snake::{ToShoutySnakeCase, ToShoutySnekCase};
-pub use snake::{ToSnakeCase, ToSnekCase};
-pub use title::ToTitleCase;
-pub use upper_camel::{ToPascalCase, ToUpperCamelCase};
+pub use kebab::{AsKebabCase, ToKebabCase};
+pub use lower_camel::{AsLowerCamelCase, ToLowerCamelCase};
+pub use shouty_kebab::{AsShoutyKebabCase, ToShoutyKebabCase};
+pub use shouty_snake::{
+    AsShoutySnakeCase, AsShoutySnakeCase as AsShoutySnekCase, ToShoutySnakeCase, ToShoutySnekCase,
+};
+pub use snake::{AsSnakeCase, AsSnakeCase as AsSnekCase, ToSnakeCase, ToSnekCase};
+pub use title::{AsTitleCase, ToTitleCase};
+pub use upper_camel::{
+    AsUpperCamelCase, AsUpperCamelCase as AsPascalCase, ToPascalCase, ToUpperCamelCase,
+};
+
+use std::fmt;
 
 use unicode_segmentation::UnicodeSegmentation;
 
-fn transform<F, G>(s: &str, with_word: F, boundary: G) -> String
+fn transform<F, G>(
+    s: &str,
+    mut with_word: F,
+    mut boundary: G,
+    f: &mut fmt::Formatter,
+) -> fmt::Result
 where
-    F: Fn(&str, &mut String),
-    G: Fn(&mut String),
+    F: FnMut(&str, &mut fmt::Formatter) -> fmt::Result,
+    G: FnMut(&mut fmt::Formatter) -> fmt::Result,
 {
     /// Tracks the current 'mode' of the transformation algorithm as it scans
     /// the input string.
@@ -83,7 +94,6 @@ where
         Uppercase,
     }
 
-    let mut out = String::new();
     let mut first_word = true;
 
     for word in s.unicode_words() {
@@ -115,9 +125,9 @@ where
                 // not uppercase and next is uppercase
                 if next == '_' || (next_mode == WordMode::Lowercase && next.is_uppercase()) {
                     if !first_word {
-                        boundary(&mut out);
+                        boundary(f)?;
                     }
-                    with_word(&word[init..next_i], &mut out);
+                    with_word(&word[init..next_i], f)?;
                     first_word = false;
                     init = next_i;
                     mode = WordMode::Boundary;
@@ -126,11 +136,11 @@ where
                 // is lowercase, word boundary before
                 } else if mode == WordMode::Uppercase && c.is_uppercase() && next.is_lowercase() {
                     if !first_word {
-                        boundary(&mut out);
+                        boundary(f)?;
                     } else {
                         first_word = false;
                     }
-                    with_word(&word[init..i], &mut out);
+                    with_word(&word[init..i], f)?;
                     init = i;
                     mode = WordMode::Boundary;
 
@@ -141,42 +151,48 @@ where
             } else {
                 // Collect trailing characters as a word
                 if !first_word {
-                    boundary(&mut out);
+                    boundary(f)?;
                 } else {
                     first_word = false;
                 }
-                with_word(&word[init..], &mut out);
+                with_word(&word[init..], f)?;
                 break;
             }
         }
     }
 
-    out
+    Ok(())
 }
 
-fn lowercase(s: &str, out: &mut String) {
+fn lowercase(s: &str, f: &mut fmt::Formatter) -> fmt::Result {
     let mut chars = s.chars().peekable();
     while let Some(c) = chars.next() {
         if c == 'Σ' && chars.peek().is_none() {
-            out.push('ς');
+            write!(f, "ς")?;
         } else {
-            out.extend(c.to_lowercase());
+            write!(f, "{}", c.to_lowercase())?;
         }
     }
+
+    Ok(())
 }
 
-fn uppercase(s: &str, out: &mut String) {
+fn uppercase(s: &str, f: &mut fmt::Formatter) -> fmt::Result {
     for c in s.chars() {
-        out.extend(c.to_uppercase())
+        write!(f, "{}", c.to_uppercase())?;
     }
+
+    Ok(())
 }
 
-fn capitalize(s: &str, out: &mut String) {
+fn capitalize(s: &str, f: &mut fmt::Formatter) -> fmt::Result {
     let mut char_indices = s.char_indices();
     if let Some((_, c)) = char_indices.next() {
-        out.extend(c.to_uppercase());
+        write!(f, "{}", c.to_uppercase())?;
         if let Some((i, _)) = char_indices.next() {
-            lowercase(&s[i..], out);
+            lowercase(&s[i..], f)?;
         }
     }
+
+    Ok(())
 }

src/lower_camel.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{capitalize, lowercase, transform};
 
 /// This trait defines a lower camel case conversion.
@@ -20,16 +22,37 @@ pub trait ToLowerCamelCase: ToOwned {
 
 impl ToLowerCamelCase for str {
     fn to_lower_camel_case(&self) -> String {
+        AsLowerCamelCase(self).to_string()
+    }
+}
+
+/// This wrapper performs a lower camel case conversion in [`fmt::Display`].
+///
+/// ## Example:
+///
+/// ```
+/// use heck::AsLowerCamelCase;
+///
+/// let sentence = "It is we who built these palaces and cities.";
+/// assert_eq!(format!("{}", AsLowerCamelCase(sentence)), "itIsWeWhoBuiltThesePalacesAndCities");
+/// ```
+pub struct AsLowerCamelCase<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for AsLowerCamelCase<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut first = true;
         transform(
-            self,
-            |s, out| {
-                if out.is_empty() {
-                    lowercase(s, out);
+            self.0.as_ref(),
+            |s, f| {
+                if first {
+                    first = false;
+                    lowercase(s, f)
                 } else {
-                    capitalize(s, out)
+                    capitalize(s, f)
                 }
             },
-            |_| {},
+            |_| Ok(()),
+            f,
         )
     }
 }

src/shouty_kebab.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{transform, uppercase};
 
 /// This trait defines a shouty kebab case conversion.
@@ -20,7 +22,25 @@ pub trait ToShoutyKebabCase: ToOwned {
 
 impl ToShoutyKebabCase for str {
     fn to_shouty_kebab_case(&self) -> Self::Owned {
-        transform(self, uppercase, |s| s.push('-'))
+        AsShoutyKebabCase(self).to_string()
+    }
+}
+
+/// This wrapper performs a kebab case conversion in [`fmt::Display`].
+///
+/// ## Example:
+///
+/// ```
+/// use heck::AsShoutyKebabCase;
+///
+/// let sentence = "We are going to inherit the earth.";
+/// assert_eq!(format!("{}", AsShoutyKebabCase(sentence)), "WE-ARE-GOING-TO-INHERIT-THE-EARTH");
+/// ```
+pub struct AsShoutyKebabCase<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for AsShoutyKebabCase<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        transform(self.0.as_ref(), uppercase, |f| write!(f, "-"), f)
     }
 }
 

src/shouty_snake.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{transform, uppercase};
 
 /// This trait defines a shouty snake case conversion.
@@ -34,7 +36,25 @@ impl<T: ?Sized + ToShoutySnakeCase> ToShoutySnekCase for T {
 
 impl ToShoutySnakeCase for str {
     fn to_shouty_snake_case(&self) -> Self::Owned {
-        transform(self, uppercase, |s| s.push('_'))
+        AsShoutySnakeCase(self).to_string()
+    }
+}
+
+/// This wrapper performs a shouty snake  case conversion in [`fmt::Display`].
+///
+/// ## Example:
+///
+/// ```
+/// use heck::AsShoutySnakeCase;
+///
+/// let sentence = "That world is growing in this minute.";
+/// assert_eq!(format!("{}", AsShoutySnakeCase(sentence)), "THAT_WORLD_IS_GROWING_IN_THIS_MINUTE");
+/// ```
+pub struct AsShoutySnakeCase<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for AsShoutySnakeCase<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        transform(self.0.as_ref(), uppercase, |f| write!(f, "_"), f)
     }
 }
 

src/snake.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{lowercase, transform};
 
 /// This trait defines a snake case conversion.
@@ -32,7 +34,25 @@ impl<T: ?Sized + ToSnakeCase> ToSnekCase for T {
 
 impl ToSnakeCase for str {
     fn to_snake_case(&self) -> String {
-        transform(self, lowercase, |s| s.push('_'))
+        AsSnakeCase(self).to_string()
+    }
+}
+
+/// This wrapper performs a snake case conversion in [`fmt::Display`].
+///
+/// ## Example:
+///
+/// ```
+/// use heck::AsSnakeCase;
+///
+/// let sentence = "We carry a new world here, in our hearts.";
+/// assert_eq!(format!("{}", AsSnakeCase(sentence)), "we_carry_a_new_world_here_in_our_hearts");
+/// ```
+pub struct AsSnakeCase<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for AsSnakeCase<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        transform(self.0.as_ref(), lowercase, |f| write!(f, "_"), f)
     }
 }
 

src/title.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{capitalize, transform};
 
 /// This trait defines a title case conversion.
@@ -20,7 +22,25 @@ pub trait ToTitleCase: ToOwned {
 
 impl ToTitleCase for str {
     fn to_title_case(&self) -> String {
-        transform(self, capitalize, |s| s.push(' '))
+        AsTitleCase(self).to_string()
+    }
+}
+
+/// This wrapper performs a title case conversion in [`fmt::Display`].
+///
+/// ## Example:
+///
+/// ```
+/// use heck::AsTitleCase;
+///
+/// let sentence = "We have always lived in slums and holes in the wall.";
+/// assert_eq!(format!("{}", AsTitleCase(sentence)), "We Have Always Lived In Slums And Holes In The Wall");
+/// ```
+pub struct AsTitleCase<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for AsTitleCase<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        transform(self.0.as_ref(), capitalize, |f| write!(f, " "), f)
     }
 }
 

src/upper_camel.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+
 use crate::{capitalize, transform};
 
 /// This trait defines an upper camel case conversion.
@@ -20,7 +22,7 @@ pub trait ToUpperCamelCase: ToOwned {
 
 impl ToUpperCamelCase for str {
     fn to_upper_camel_case(&self) -> String {
-        transform(self, capitalize, |_| {})
+        AsUpperCamelCase(self).to_string()
     }
 }
 
@@ -37,6 +39,24 @@ impl<T: ?Sized + ToUpperCamelCase> ToPascalCase for T {
     }
 }
 
+/// This wrapper performs a upper camel case conversion in [`fmt::Display`].
+///
+/// ## Example:
+///
+/// ```
+/// use heck::AsUpperCamelCase;
+///
+/// let sentence = "We are not in the least afraid of ruins.";
+/// assert_eq!(format!("{}", AsUpperCamelCase(sentence)), "WeAreNotInTheLeastAfraidOfRuins");
+/// ```
+pub struct AsUpperCamelCase<T: AsRef<str>>(pub T);
+
+impl<T: AsRef<str>> fmt::Display for AsUpperCamelCase<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        transform(self.0.as_ref(), capitalize, |_| Ok(()), f)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::ToUpperCamelCase;