Errors

ada.rs

/// crate gpio_mmap
/// mod gpio_mmap
pub trait GpioMmap {
    type Error: Fail;
    type Register;

    fn new(...) -> Result<Self, Self::Error> where Self: Sized;
    fn registers(&self) -> &[Self::Register];
}

/// crate raspbian_osal
/// mod raspbial_gpio_mmap
/// Mmap is defined in an external crate (memmap::Mmap on crates.io); details not relevant (I hope) ;)
pub struct RaspbianGpioMmap {
    mmap: Mmap,
    ...
}

impl GpioMmap for RaspbianGpioMmap {
    type Error = Error;
    type Register = Register;

    fn new(...) -> Result<Self> {
        ...
    }

    fn registers(&self) -> &[Self::Register] {
        assert_ne!(size_of::<Self::Register>(), 0, "{}", MSG_ERR_INTERNAL_ZERO_SIZED_REGISTER_TYPE);
        unsafe {
            slice::from_raw_parts(self.mmap.ptr() as *const Self::Register,
                                  self.mmap.len() * size_of::<u8>() / size_of::<Self::Register>())
        }
    }
}

/// mod raspbian_osal
pub struct RaspbianOsal<'a> {
    gpio_registers: &'a [Register],
}

impl<'a> Osal<'a> for RaspbianOsal<'a> {
    type Error = Error;
    type Register = Register;

    fn new<T>(gpio_mmap: &'a T) -> Result<Self> where T: GpioMmap<Register = Self::Register>,
                                                      Self: Sized, {
        Ok(Self {
            gpio_registers: gpio_mmap.registers(),
        })
    }
    ...
}

/// crate rpi3_chal
pub struct Rpi3ChalRaspbianOsalTestContainer {
    ...
    pub gpio_mmap: Option<RaspbianGpioMmap>,
}

impl Rpi3ChalRaspbianOsalTestContainer {
    pub fn build() -> Self {
        ...
        let mut container = Self {
            ...
            gpio_mmap: None,
        };
        container.resolve_gpio_mmap_once();
        container
    }

    pub fn resolve_gpio_mmap_once(&mut self) -> Result<()> {
        match self.mmap_already_instantiated.compare_and_swap(false, true, Ordering::Relaxed) {
            true => Err(Error::SingletonViolation.context(MSG_GPIO_MMAP))?,
            false => {
                self.gpio_mmap = Some(RaspbianGpioMmap::new(&RASPBIAN_GPIO_DEVICE_ID,
                                                        RPI3_GPIO_BASE,
                                                        RPI3_GPIO_REGISTER_COUNT)?);
                Ok(())
            },
        }
    }

    pub fn resolve_osal_once(&mut self) -> Result<RaspbianOsal> {
        match self.osal_already_instantiated.compare_and_swap(false, true, Ordering::Relaxed) {
            true => Err(Error::SingletonViolation.context(MSG_RASPBIAN_OSAL))?,
            false => Ok(RaspbianOsal::new(&self.gpio_mmap.expect(MSG_ERR_INTERNAL_MMAP_CACHE))?),   // <- this is the offending line ("line 56" in the error message below)
        }
    }
    
    ...
}

/// Here's the resulting error message:
```rust
error[E0597]: borrowed value does not live long enough
  --> rpi3_chal/src/unit_tests/di.rs:56:44
   |
56 |             false => Ok(RaspbianOsal::new(&self.gpio_mmap.expect(MSG_ERR_INTERNAL_MMAP_CACHE))?),
   |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  - temporary value only lives until here
   |                                            |
   |                                            temporary value does not live long enough
   |
note: borrowed value must be valid for the anonymous lifetime #1 defined on the method body at 53:5...
  --> rpi3_chal/src/unit_tests/di.rs:53:5
   |
53 | /     pub fn resolve_osal_once(&mut self) -> Result<RaspbianOsal> {
54 | |         match self.osal_already_instantiated.compare_and_swap(false, true, Ordering::Relaxed) {
55 | |             true => Err(Error::SingletonViolation.context(MSG_RASPBIAN_OSAL))?,
56 | |             false => Ok(RaspbianOsal::new(&self.gpio_mmap.expect(MSG_ERR_INTERNAL_MMAP_CACHE))?),
57 | |         }
58 | |     }
   | |_____^

error[E0509]: cannot move out of type `unit_tests::di::Rpi3ChalRaspbianOsalTestContainer`, which implements the `Drop` trait
  --> rpi3_chal/src/unit_tests/di.rs:56:44
   |
56 |             false => Ok(RaspbianOsal::new(&self.gpio_mmap.expect(MSG_ERR_INTERNAL_MMAP_CACHE))?),
   |                                            ^^^^^^^^^^^^^^ cannot move out of here

error: aborting due to 2 previous errors

error: Could not compile `rpi3_chal`.

/// I would have expected the ref to have been captured and stored.  Its referent outlives the function call.  How do I tell the compiler that this is OK?