doc: add examples for borsh::to_vec, borsh::to_writer, borsh::object_length (#238)

Author: dj8yfo

borsh/src/ser/helpers.rs

@@ -5,6 +5,11 @@ use crate::io::{ErrorKind, Result, Write};
 pub(super) const DEFAULT_SERIALIZER_CAPACITY: usize = 1024;
 
 /// Serialize an object into a vector of bytes.
+/// # Example
+///
+/// ```
+/// assert_eq!(vec![12, 0, 0, 0, 0, 0, 0, 0], borsh::to_vec(&12u64).unwrap());
+/// ```
 pub fn to_vec<T>(value: &T) -> Result<Vec<u8>>
 where
     T: BorshSerialize + ?Sized,
@@ -15,6 +20,14 @@ where
 }
 
 /// Serializes an object directly into a `Writer`.
+/// # Example
+///
+/// ```
+/// # #[cfg(feature = "std")]
+/// let stderr = std::io::stderr();
+/// # #[cfg(feature = "std")]
+/// assert_eq!((), borsh::to_writer(&stderr, "hello_0x0a").unwrap());
+/// ```
 pub fn to_writer<T, W: Write>(mut writer: W, value: &T) -> Result<()>
 where
     T: BorshSerialize + ?Sized,
@@ -23,6 +36,26 @@ where
 }
 
 /// Serializes an object without allocation to compute and return its length
+/// # Example
+///
+/// ```
+/// use borsh::BorshSerialize;
+///
+/// /// derive is only available if borsh is built with `features = ["derive"]`
+/// # #[cfg(feature = "derive")]
+/// #[derive(BorshSerialize)]
+/// struct A {
+///     tag: String,
+///     value: u64,
+/// };
+///
+/// # #[cfg(feature = "derive")]
+/// let a = A { tag: "hello".to_owned(), value: 42 };
+///
+/// assert_eq!(8, borsh::object_length(&12u64).unwrap());
+/// # #[cfg(feature = "derive")]
+/// assert_eq!(17, borsh::object_length(&a).unwrap());
+/// ```
 pub fn object_length<T>(value: &T) -> Result<usize>
 where
     T: BorshSerialize + ?Sized,