Improve error handling in the `raw` and `screen` modules

- Ignore errors in `Drop` implementations.
- Replace `AlternateScreen::from` with an `IntoAlternateScreen` trait
  which doesn't panic on errors, to make the API more consistent with
  the `raw` module.

examples/alternate_screen.rs

@@ -1,12 +1,12 @@
 extern crate termion;
 
-use termion::screen::*;
+use termion::screen::IntoAlternateScreen;
 use std::io::{Write, stdout};
 use std::{time, thread};
 
 fn main() {
     {
-        let mut screen = AlternateScreen::from(stdout());
+        let mut screen = stdout().into_alternate_screen().unwrap();
         write!(screen, "Welcome to the alternate screen.\n\nPlease wait patiently until we arrive back at the main screen in a about three seconds.").unwrap();
         screen.flush().unwrap();
 

examples/alternate_screen_raw.rs

@@ -3,7 +3,7 @@ extern crate termion;
 use termion::event::Key;
 use termion::input::TermRead;
 use termion::raw::IntoRawMode;
-use termion::screen::*;
+use termion::screen::{IntoAlternateScreen, ToAlternateScreen, ToMainScreen};
 use std::io::{Write, stdout, stdin};
 
 fn write_alt_screen_msg<W: Write>(screen: &mut W) {
@@ -16,7 +16,7 @@ fn write_alt_screen_msg<W: Write>(screen: &mut W) {
 
 fn main() {
     let stdin = stdin();
-    let mut screen = AlternateScreen::from(stdout().into_raw_mode().unwrap());
+    let mut screen = stdout().into_raw_mode().unwrap().into_alternate_screen().unwrap();
     write!(screen, "{}", termion::cursor::Hide).unwrap();
     write_alt_screen_msg(&mut screen);
 

src/raw.rs

@@ -42,7 +42,7 @@ pub struct RawTerminal<W: Write> {
 
 impl<W: Write> Drop for RawTerminal<W> {
     fn drop(&mut self) {
-        set_terminal_attr(&self.prev_ios).unwrap();
+        let _ = set_terminal_attr(&self.prev_ios);
     }
 }
 

src/screen.rs

@@ -6,12 +6,12 @@
 //! # Example
 //!
 //! ```rust
-//! use termion::screen::AlternateScreen;
+//! use termion::screen::IntoAlternateScreen;
 //! use std::io::{Write, stdout};
 //!
 //! fn main() {
 //!     {
-//!         let mut screen = AlternateScreen::from(stdout());
+//!         let mut screen = stdout().into_alternate_screen().unwrap();
 //!         write!(screen, "Writing to alternate screen!").unwrap();
 //!         screen.flush().unwrap();
 //!     }
@@ -51,18 +51,22 @@ pub struct AlternateScreen<W: Write> {
     output: W,
 }
 
-impl<W: Write> AlternateScreen<W> {
-    /// Create an alternate screen wrapper struct for the provided output and switch the terminal
-    /// to the alternate screen.
-    pub fn from(mut output: W) -> Self {
-        write!(output, "{}", ToAlternateScreen).expect("switch to alternate screen");
-        AlternateScreen { output: output }
+/// Extension trait for writers, providing the `into_alternate_screen` function.
+pub trait IntoAlternateScreen: Write + Sized {
+    /// Switch the terminal controlled by this writer to use the alternate screen. The terminal will be
+    /// restored to the main screen when the `AlternateScreen` returned by this function is
+    /// dropped.
+    fn into_alternate_screen(mut self) -> io::Result<AlternateScreen<Self>> {
+        write!(self, "{}", ToAlternateScreen)?;
+        Ok(AlternateScreen { output: self })
     }
 }
 
+impl<W: Write> IntoAlternateScreen for W {}
+
 impl<W: Write> Drop for AlternateScreen<W> {
     fn drop(&mut self) {
-        write!(self, "{}", ToMainScreen).expect("switch to main screen");
+        let _ = write!(self, "{}", ToMainScreen);
     }
 }