1 files changed, 50 insertions, 0 deletions
diff --git a/vendor/mac/src/format.rs b/vendor/mac/src/format.rs
new file mode 100644
index 000000000..8d4c8bb09
--- /dev/null
+++ b/vendor/mac/src/format.rs
@@ -0,0 +1,50 @@
+//! Macros for string formatting.
+
+/// Conditionally perform string formatting.
+///
+/// If `$enabled` is true, then do the formatting and return a `Cow::Owned`.
+///
+/// Otherwise, just return the borrowed (often `'static`) string
+/// `$borrowed`.
+///
+/// When `$enabled` is false, this avoids the overhead of allocating
+/// and writing to a buffer, as well as any overhead or side effects
+/// of the format arguments.
+///
+/// # Example
+///
+/// You can use `format_if` to implement a detailed error logging facility
+/// that can be enabled at runtime.
+///
+/// ```
+/// # #[macro_use] extern crate mac;
+/// # use std::borrow::Cow::{Borrowed, Owned};
+/// # fn main() {
+/// let formatted = format_if!(true, "Vague error", "Error code {:?}", 3);
+///
+/// assert_eq!(&formatted[..], "Error code 3");
+/// if let Borrowed(_) = formatted {
+///     panic!("Wrong!")
+/// }
+///
+/// let not_formatted = format_if!(false, "Vague error", "Error code {:?}", {
+///     // Note that the argument is not evaluated.
+///     panic!("oops");
+/// });
+///
+/// assert_eq!(&not_formatted[..], "Vague error");
+/// if let Owned(_) = not_formatted {
+///     panic!("Wrong!")
+/// }
+/// # }
+/// ```
+#[macro_export]
+macro_rules! format_if {
+    ($enabled:expr, $borrowed:expr, $fmt:expr, $($args:expr),*) => {
+        if $enabled {
+            ::std::borrow::Cow::Owned(format!($fmt, $($args),*)) as ::std::borrow::Cow<str>
+        } else {
+            ::std::borrow::Cow::Borrowed($borrowed)
+        }
+    }
+}