chore: util methods

Author: prestwich

Cargo.toml

@@ -4,7 +4,7 @@ name = "init4-bin-base"
 description = "Internal utilities for binaries produced by the init4 team"
 keywords = ["init4", "bin", "base"]
 
-version = "0.3.0"
+version = "0.3.1"
 edition = "2021"
 rust-version = "1.81"
 authors = ["init4", "James Prestwich"]

src/utils/from_env.rs

@@ -346,6 +346,45 @@ pub trait FromEnvVar: core::fmt::Debug + Sized + 'static {
 
     /// Load the primitive from the environment at the given variable.
     fn from_env_var(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>;
+
+    /// Load the primitive from the environment at the given variable. If the
+    /// variable is unset or empty, return the default value.
+    ///
+
+    fn from_env_var_or(env_var: &str, default: Self) -> Result<Self, FromEnvErr<Self::Error>> {
+        match Self::from_env_var(env_var) {
+            Ok(v) => Ok(v),
+            Err(FromEnvErr::Empty(_)) | Err(FromEnvErr::EnvError(_, _)) => Ok(default),
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Load the primitive from the environment at the given variable. If the
+    /// variable is unset or empty, call the provided function to get the
+    /// default value.
+    ///
+    /// This function will return an error if the environment variable is set
+    /// but cannot be parsed.
+    fn from_env_var_or_else(
+        env_var: &str,
+        default: impl FnOnce() -> Self,
+    ) -> Result<Self, FromEnvErr<Self::Error>> {
+        match Self::from_env_var(env_var) {
+            Ok(v) => Ok(v),
+            Err(FromEnvErr::Empty(_)) | Err(FromEnvErr::EnvError(_, _)) => Ok(default()),
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Load the primitive from the environment at the given variable. If the
+    /// variable is unset or empty, return the value generated by
+    /// [`Default::default`].
+    fn from_env_var_or_default(env_var: &str) -> Result<Self, FromEnvErr<Self::Error>>
+    where
+        Self: Default,
+    {
+        Self::from_env_var_or_else(env_var, Self::default)
+    }
 }
 
 impl<T> FromEnvVar for Option<T>