use std::collections::{BTreeMap, HashMap};
use std::hash::BuildHasher;
pub trait VariableMap<'a> {
type Value;
fn get(&'a self, key: &str) -> Option<Self::Value>;
}
#[derive(Debug)]
pub struct NoSubstitution;
impl<'a> VariableMap<'a> for NoSubstitution {
type Value = NeverValue;
#[inline]
fn get(&'a self, _key: &str) -> Option<Self::Value> {
None
}
}
#[derive(Debug)]
pub enum NeverValue {}
impl<T: ?Sized> AsRef<T> for NeverValue {
#[inline]
fn as_ref(&self) -> &T {
match *self {
}
}
}
#[derive(Debug)]
pub struct Env;
impl<'a> VariableMap<'a> for Env {
type Value = String;
#[inline]
fn get(&'a self, key: &str) -> Option<Self::Value> {
std::env::var(key).ok()
}
}
#[cfg(unix)]
#[derive(Debug)]
pub struct EnvBytes;
#[cfg(unix)]
impl<'a> VariableMap<'a> for EnvBytes {
type Value = Vec<u8>;
#[inline]
fn get(&'a self, key: &str) -> Option<Self::Value> {
use std::os::unix::ffi::OsStringExt;
let value = std::env::var_os(key)?;
Some(value.into_vec())
}
}
impl<'a, V: 'a> VariableMap<'a> for BTreeMap<&str, V> {
type Value = &'a V;
#[inline]
fn get(&'a self, key: &str) -> Option<Self::Value> {
self.get(key)
}
}
impl<'a, V: 'a> VariableMap<'a> for BTreeMap<String, V> {
type Value = &'a V;
#[inline]
fn get(&'a self, key: &str) -> Option<Self::Value> {
self.get(key)
}
}
impl<'a, V: 'a, S: BuildHasher> VariableMap<'a> for HashMap<&str, V, S> {
type Value = &'a V;
#[inline]
fn get(&'a self, key: &str) -> Option<Self::Value> {
self.get(key)
}
}
impl<'a, V: 'a, S: BuildHasher> VariableMap<'a> for HashMap<String, V, S> {
type Value = &'a V;
#[inline]
fn get(&'a self, key: &str) -> Option<Self::Value> {
self.get(key)
}
}