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// Copyright 2020 The Fuchsia Authors
//
// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
// This file may not be copied, modified, or distributed except according to
// those terms.

//! The Unless trait for a more fluent use of Option::unwrap_or().
//!
//! Specificially, this is intended to be used in cases where the "default" value is almost always
//! the value in use, and the Option is rarely set.
//!
//! ```
//! use omaha_client::unless::Unless;
//! // This implies that |some_option| is usually set, and "default" is there in case it's not.
//! let some_option_usually_set = Some("string");
//! let value = some_option_usually_set.unwrap_or("default");
//! assert_eq!("string", value);
//!
//! // Whereas this implies that "default" is the common case, and |some_option| is an override.
//! let some_option_usually_unset = None;
//! let value = "default".unless(some_option_usually_unset);
//! assert_eq!("default", value);
//! ```

pub trait Unless: Sized {
    // unless returns the value of self, unless the option is Some value.
    //
    // # Example
    //
    // ```
    // assert_eq!("default", "default".unless(None));
    // assert_eq!("other", "default".unless(Some("other")));
    // ```
    fn unless(self, option: Option<Self>) -> Self;
}

/// Provide a blanket implementation for all Sized types.
impl<T: Sized> Unless for T {
    fn unless(self, option: Option<Self>) -> Self {
        option.unwrap_or(self)
    }
}

#[cfg(test)]
mod tests {
    use super::Unless;

    #[test]
    fn tests() {
        assert_eq!("default", "default".unless(None));
        assert_eq!("other", "default".unless(Some("other")));
    }
}