Struct DebugOnly 

#[repr(C)]
pub struct DebugOnly<T> {
    pub _phantom_0: PhantomData<UnsafeCell<T>>,
    pub value: T,
}

DebugOnly contains a value of type T, but only in debug builds. In release builds, it does not contain a value. This helper is intended to be used with MOZ_ASSERT()-style macros, allowing one to write:

DebugOnly check = func(); MOZ_ASSERT(check);

more concisely than declaring |check| conditional on #ifdef DEBUG.

DebugOnly instances can only be coerced to T in debug builds. In release builds they don’t have a value, so type coercion is not well defined.

NOTE: DebugOnly instances still take up one byte of space, plus padding, even in optimized, non-DEBUG builds (see bug 1253094 comment 37 for more info). For this reason the class is MOZ_STACK_CLASS to prevent consumers using DebugOnly for struct/class members and unwittingly inflating the size of their objects in release builds.

Fields

_phantom_0: PhantomData<UnsafeCell<T>>

value: T

Trait Implementations

impl<T> Debug for DebugOnly<T>

where T: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl<T> PartialEq for DebugOnly<T>

where T: PartialEq,

fn eq(&self, other: &DebugOnly<T>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T> StructuralPartialEq for DebugOnly<T>

Layout

Note: Unable to compute type layout, possibly due to this type having generic parameters. Layout can only be computed for concrete, fully-instantiated types.